The user wants creative code for an RP2350 (Raspberry Pi Pico 2) that generates a synthesizer sound passed to I2S, with user interaction. Let me think about this. The RP2350 is the chip on the Raspberry Pi Pico 2. It's dual-core Cortex-M33 (or RISC-V Hazard3). For sound output, we need I2S. The Pico SDK has `pico_audio_i2s` library, but a simpler approach many people use is a bit-banged or PIO-based I2S output. PIO is perfect for I2S — the Pico examples include an audio_i2s example using PIO. Since we can't rely on pico_extras (audio_i2s library), let's write our own PIO-based I2S output. That's self-contained: a PIO program that shifts out 32-bit samples (16-bit stereo) with BCK, LRCK, DATA pins. The classic example: ```pio .program i2s_out .side_set 2 ; Pin assignments: ; 0: data ; 1: bit clock ; out pins, 2 sideset... ``` Actually the canonical pico-examples audio_i2s PIO program: ``` .program i2s_out .side_set 2 ; ┌───┐ ┌───┐ ; BCK ───┘ └───────────┘ └─── ; ──┐ ┌───────┐ ; LRCLK └───────────┘ └── (left when low? etc) ``` The standard one from pico-examples (audio_i2s): ```pio .program i2s_out .side_set 2 ; ┌─────┐ ┌─────┐ ; BCK ──┘ └─────────────┘ └── ; ───┐ ┌───────────┐ ; LRCLK └─────────────┘ └─── ; ┌─────────────────────────┐ ; DATA └──────────────────────────┘ ... start: set x, 14 side 0b01 dataloop: out pins, 1 side 0b00 [1] jmp x--, dataloop side 0b01 out pins, 1 side 0b10 set x, 14 side 0b11 dataloop16: out pins, 1 side 0b10 jmp x--, dataloop16 side 0b11 jmp start side 0b00 ``` Hmm, let me recall the actual example. From pico-examples pio/audio_i2s/audio_i2s.pio: ```pio ; ; ────────────────┐ ┌───────────────┐ ──────────────── ; │ │ │ ; 1 ┌───┐ ┌───┐ ; BCK ──────────┘ └─────────┘ └─── ... ; (etc.) ``` The actual code: ```pio .program i2s_out .side_set 2 ; ┌─────────────────┐ ┌───────────── ; DATA ─┘ └─────────┘ ; ... start: set x, 14 side 0b01 left_data_loop: out pins, 1 side 0b00 jmp x-- left_data_loop side 0b01 out pins, 1 side 0b10 set x, 14 side 0b11 right_data_loop: out pins, 1 side 0b10 jmp x-- right_data_loop side 0b11 jmp start side 0b00 ``` Wait — sideset is 2 bits: bit0 = data? No. Let me recall. In the example: - sideset bits: bit 0 = data (DIN), bit 1 = BCK? Hmm. Actually in pico-examples audio_i2s.pio: ``` ; ┌── 16 bits ──┐ ; ... ; ─────────┐ ┌────────────┐ ┌───── ; BCK └───┘ └───┘ ; ... ; Data is output MSB first, on the rising edge of BCK... ``` The pio program (I remember it fairly well): ``` .program i2s_out .side_set 2 ; ┌───┐ ┌───┐ ; BCK ──┘ └──────────┘ └── ; ────┐ ┌──── ; LRCK └──────────┘ start: set x, 14 side 0b01 ; LRCK high, BCK low? data16: out pins, 1 side 0b00 jmp x-- data16 side 0b01 out pins, 1 side 0b10 set x, 14 side 0b11 data16_2: out pins, 1 side 0b10 jmp x-- data16_2 side 0b11 jmp start side 0b00 ``` Hmm, I'm not 100% sure of the sideset bit assignment. Let me design my own instead, so correctness doesn't depend on memory. Let's define: - Pin 0 (base+0): DIN (data) - Pin 1 (base+1): BCK - Pin 2 (base+2): LRCK Approach: sideset 2 pins where sideset base = BCK pin? Actually sideset must be contiguous pins starting at... sideset has its own base. Let me use a simpler scheme: I'll write a PIO program that manually drives all three pins via `out pins` on a 3-bit basis? That's slower. Better: use sideset for BCK toggle and `out pins` for data... but data and BCK need to be different pin groups. Simplest robust design: use `sideset` 2 bits: bit0 = DIN? No — sideset pins must be contiguous and the top one toggles... Let me just carefully design: Design A: Use PIO with: - out pins mapped to 1 pin: DIN. - sideset 1 pin: BCK. - LRCK driven by... needs a third pin. Could be driven by the second sideset bit if sideset=2: sideset pins [BCK, LRCK]? But sideset changes only when we set them; LRCK needs to alternate at frame boundary — we can do that with explicit side values at different points in the program. So: pins assigned: DIN = base+? Actually `out pins` uses the "out" pin group base, which can differ from sideset base. Let me set: - Sideset base: pin 1 (BCK), 2 pins: sideset bits [BCK, LRCK]. So sideset value 0b00 = BCK low, LRCK low; 0b01 = BCK low, LRCK high; 0b10 = BCK high, LRCK low; 0b11 = BCK high, LRCK high. - Out pins base: pin 0 (DIN), 1 bit wide. I2S Philips format: data MSB first, data valid on falling edge of BCK, LRCK transitions on falling edge of BCK; when LRCK is low = left channel (typically), data for left channel is clocked out during the 16 BCK cycles while LRCK low... Actually in standard I2S, LRCK (WS) low = left, data changes on falling edge, MSB first, MSB is presented one BCK after WS transition. Typical DAC (e.g., PCM1808/PCM5102, MAX98357A): On falling edge of BCK, data transitions; DAC samples on rising edge. WS changes on falling edge. First bit after WS change appears one BCK later. So the sequence per channel: Set data bit while BCK low, then raise BCK (DAC latches on rising edge), then lower BCK and change data. Let me write PIO: ``` .program i2s_out .side_set 2 ; sideset: bit0 -> BCK? no wait, sideset bits map MSB first to consecutive pins. ``` Hmm: sideset base pin and `sideset pindirs` etc. With `.side_set 2`, the sideset field is 2 bits, written to pins (base + 0) and (base + 1). The MSB of the side value goes to base+0? Actually side-set bits: the least significant bit of the side value is applied to the lowest pin? Let me recall: "The side-set base pin... bit 0 of the side-set value is applied to the base pin, bit 1 to base+1"? I believe sideset LSB → base pin. Hmm, actually I think for sideset, the side-set data is shifted... In the SDK, `sm_config_set_sideset_pins` sets base. The side value written e.g. `side 3` with 2 sideset bits puts value 3 on the two pins: bit0 of 3 → base pin, bit1 → base+1. I'm fairly sure it's LSB to base pin. Wait, no — I recall it's the opposite: the side-set bits are the *top* bits of the instruction, and they map... Let me think about the `out` command: `out pins, N` — bits shifted out of OSR LSB-first go to out pin base upward (LSB first to lowest pin). For sideset, similarly I'd expect LSB → base pin. Hmm, but actually I recall reading that side-set MSB goes to the base pin. Let me check the known example: audio_i2s.pio comments: From pico-examples/audio_i2s/audio_i2s.pio: ``` .program i2s_out .side_set 2 ; ┌───────────────┐ ┌─────── ; DATA └───────────────┘ └─────── ; (...) ; ; Pin config: ; 0: data ; 1: BCK ; 2: LRCK ``` Hmm wait, actually I think the example uses sideset with pins... Let me recall the actual text: ``` ; ──┐ ┌──────────┐ ┌── ; │ │ │ │ ; BCK ... ``` I remember the actual program is: ``` .program i2s_out .side_set 2 start: set x, 14 side 0b01 bitloop1: out pins, 1 side 0b00 jmp x-- bitloop1 side 0b01 out pins, 1 side 0b10 set x, 14 side 0b11 bitloop2: out pins, 1 side 0b10 jmp x-- bitloop2 side 0b11 jmp start side 0b00 ``` Hmm wait — but that has sideset 2 bits and the side values 0b00,0b01,0b10,0b11. And pins: 0=data? If sideset base is pin 0... no. Let me look at it from the example's pin config comment: Actually from pico-examples repo, audio_i2s.pio: ``` ; ; ──────────┐ ┌─────────┐ ┌─────────┐ ; ┌───┐ ┌───┐ ┌─── ; DATA ─┘ └─────────┘ └─────────┘ ; ; ... ; ────────── ; LRCK ... .program i2s_out .side_set 2 ; Pin assignments: ; 0: data ; 1: bit clock ; 2: LR clock ; ; The first `out` instruction... ``` Hmm honestly I don't remember exactly. I recall the example config in C: ```c pio_sm_config c = i2s_out_program_get_default_config(offset); sm_config_set_out_pins(&c, PIN_DATA, 1); sm_config_set_sideset_pins(&c, PIN_BCK); // ? ``` Actually the real example: ```c static const struct pio_program i2s_out... ``` Let me just design my own and verify with my own reasoning rather than recalling. I'll define my own PIO program with explicit correctness analysis. My design: Pins: DIN = base+0, BCK = base+1, LRCK = base+2. Use sideset of 2 pins at base+1 and base+2? With side value bits: which bit goes where? Side-set bit 0 → base+... To avoid confusion, let me test logic: In `audio_i2s.pio` from pico-extras... Let me think about a simpler alternative: use `out pins, 3` writing DIN, BCK, LRCK all from OSR? That wastes OSR bits massively (3 bits per instruction = 32 bits per ~32 cycles → sample rate limited). Not great. Alternative simpler approach: Instead of side-set for clocks, drive BCK/LRCK from... Actually a cleaner known-good approach: use the pico-extras `audio_i2s` library. But that requires pico-extras and my memory of its API (`audio_i2s_setup`, etc.) is fuzzy-ish. I know it: ```c #include "pico/audio_i2s.h" audio_i2s_config_t config = { .data_pin = PICO_AUDIO_I2S_DATA_PIN? ... }; ``` Hmm, the pico-extras audio API: `audio_i2s_setup(&config)`, `audio_i2s_set_buffer_size`, then `queue` via `audio_i2s_connect`... It's `struct audio_i2s *audio_i2s_setup(...)`. My memory: ```c audio_i2s_config_t i2s_config = { .data_pin = 9, .clock_pin_base = 10, .dma_channel = -1, .pio_sm = -1, }; example_audio_i2s_setup... ``` Then `audio_i2s_set_buffer_size`? And you push `audio_buffer_t` filled with int16 stereo samples. The exact API: `audio_i2s_init`, `audio_i2s_connect`, `audio_i2s_connect_external`? I recall: ```c struct audio_i2s *audio_i2s_setup(uint32_t sample_rate?...)? ``` Hmm. Rather than risk wrong API from pico-extras, writing our own PIO I2S is more robust and more instructive/creative. I'll write my own and verify its correctness by reasoning through timing. Let me define the PIO program from scratch, using explicit `set`/`out` with sideset for BCK and LRCK. Pin mapping plan: - out pin: DIN at base D (single pin). - sideset pins (2): base B = BCK, B+1 = LRCK. Question: with `.side_set 2`, side value `side v` — bit 0 of v goes to base B, bit 1 goes to base B+1? Or reversed? From RP2040 datasheet (RP2350 same): "Side Set... The side-set bits are the most significant bits of the delay/side-set field..." The side-set field value: when an instruction has side-set, the SIDESET bits are written to consecutive GPIOs starting at the side-set base pin. The mapping: LSB of side value → base pin? Consider the delay/sideset encoding: For `sideset_opt` etc., the value stored in the instruction is shifted so that the lowest side-set bit is adjacent... In the assembled instruction, side-set occupies the top bits of the 5-bit delay/side field. E.g., with 2 side-set bits: bits [4:3] of the delay field are side-set values, with bit 3 = sideset bit0 (lowest), bit 4 = sideset bit1? Hmm, that means value written `side 0b10` → sideset bit0 = 0, bit1 = 1 → pin base = 0, base+1 = 1. I believe: `side N` where the low bit of N goes to the base pin. Actually let me verify with a known example: `ws2812.pio` uses 1 side-set pin for the data... not helpful. `uart_tx.pio`? Uses `set x, 7` and `out pins, 1`... no sideset. `spi` examples? Hmm. The `pwm` example? Let me think of `apio`? OK here's another known one: `pio_blink`? no. Known: `bubble_sort`? no sideset. Hmm, `manchester_encoding`? uses out pins. `clocked_input`? ` sideset`? Let me reason from the assembler: In pioasm, `side 3` with 2 side-set bits produces delay field bits = (3 << 3) | delay. So instruction word bits [6:5]? The delay/sideset field is bits [7:3]... wait PIO instruction layout: bits [12:8] = delay/sideset (5 bits), bits [7:0]? No: PIO instruction is 16 bits: bits [15:13] = opcode, [12:8] = delay/side-set, [7:0] operands. The 5-bit delay/side field: bits [4:0] of that field: with 2 sideset bits, sideset occupies [4:3], delay [2:0]. `side 0b10` means the side value 2 → written into bits [4:3] as value 2 → bit4=1, bit3=0. At runtime, hardware writes sideset bits to pins: "the most-significant side-set bit is applied to the lowest-numbered GPIO in the side-set pin group"? or LSB to lowest pin? RP2040 datasheet 3.4.2: "The side-set bits are output on the side-set base pin... with the LSB... " Argh. RP2040 datasheet, section on side set: "Side Set: ... up to 5 bits ... can be used to generate e.g. a serial interface clock... When executing, the side-set bits are written to the pins... **the least significant side-set bit is presented on the side-set base pin**"? Hmm, I genuinely recall the opposite statement in the RP2350 datasheet: "Note the side-set bits are applied MSB-first..." Let me settle it with the audio_i2s example which I partially remember: pico-examples audio_i2s.pio: ``` .program i2s_out .side_set 2 ; ┌─────────────────┐ ; DATA ───┘ └──────... ; ... ; 0: DATA ; 1: BCK ; 2: LRCL ; ; Note: with side_set 2, sideset bits go to pins 1 and 2 (sideset base = 1)? ``` Hmm, and its C: ```c sm_config_set_out_pins(&c, PIO_PIN_DATA?...) ``` OK alternative memory: I actually recall the audio_i2s.pio content now: ``` ; ┌───────────────┐ ┌───── ; DATA └───────────────┘ └───── ... ; ; ┌──┐ ┌──┐ ┌──┐ ┌──┐ ; BCK ─┘ └─────┘ └─────┘ └─────┘ └── ; ────────┐ ┌─────────── ; LRCL └─────────────┘ ``` and the program: ``` start: set x, 14 side 0b11 data0: out pins, 1 side 0b10 jmp x-- data0 side 0b11 ``` I'm going in circles. New approach: avoid sideset ambiguity entirely by using explicit `set pins`/`mov pins` operations with a 3-bit pin mapping via `out`? Actually simplest bulletproof: use sideset with 1 pin for BCK toggling... but LRCK also needs toggling — could use a second PIO SM! SM0 = I2S data+BCK, SM1 = LRCK generator? Or: LRCK can be generated by... Actually another classic trick: LRCK = BCK/64 via a counter... overkill. Cleanest bulletproof: verify side-set pin mapping from first principles using the RP2040/RP2350 datasheet statement which I'll now try hard to recall. RP2040 datasheet section 3.4.1? "By default PIO... 32-bit shift..." Not that. The side-set section: "Side Set ... A side-set of up to 5 bits ... The most-significant side-set bit always... " Hmm. Actually! I remember concretely now: In `pio_i2s` implementations floating around (e.g., from the `pico_audio_i2s` in pico-extras), the file audio_i2s.pio says: ``` ; -------------------------------------------------------------- # ; NOTE: # ; This is 16-bit stereo audio. # ; ... # ; Pin assignments: # ; 0: DATA # ; 1: BCK # ; 2: LRCK (BCK+1) # ``` and C code: ```c sm_config_set_out_pin_base? ``` Hmm no. OK, decision: I'll design the program so the side-set mapping ambiguity doesn't matter, by using side-set values that are symmetric or by testing both interpretations? Can't test in my head... Actually I can: I'll design so that with **either** mapping of sideset bits to pins, the output is still valid I2S. That's hard. Alternative: skip sideset. Use `set pindirs`? Use explicit approach with `out pins, 1` for data and `set pins` for clocks? `set pins` writes `set` operand bits to pins (SET pin group). So I could map: SET pin group = {BCK, LRCK} (base+1, base+2, 2 bits), OUT pin group = DIN (base+0, 1 bit). `set pins, 3` writes value 3 → LSB→base+1? Same ambiguity!! `set pins` with 2 pins: "the source data is written... LSB first to base pin"? For `set pins`, datasheet says the SET pin group: "the set pins... The 5-bit value from the SET instruction... " Ugh, same question. Hmm, but wait: for `out pins, N`, the datasheet explicitly says data is shifted out **LSB-first onto the lowest numbered pin**. Actually it says "Writing to pins: data is written to the mapped pins, LSB first"? For OUT, "out pins" writes N bits taken LSB-first from OSR to the out pin group starting at base. I'm fairly confident: `out pins, 1` shifts 1 bit (OSR LSB) to out base pin. For multi-bit, OSR bit0→base, bit1→base+1... I believe that's right (LSB to lowest pin). For `set pins`: the 5-bit immediate... hmm. Datasheet: "SET: ... write the immediate value to the SET pin group..." I believe also LSB→base pin. And for sideset: RP2040 datasheet 3.4.?: "Side-set base... the side-set bits are the **most significant** bits..." no wait, that's about instruction encoding. Let me try recalling an authoritative simple example: `ws2812.pio` has: ``` .side_set 1 ... public entry: ... out x, 1 side 0 [5] ; side 0 = drive pin low ... out x, 1 side 1 [3] ... ``` Wait actually ws2812 pio uses sideset as the DATA pin: `side 1` = high, `side 0` = low, with sideset base = the WS2812 data pin. Only 1 bit so no mapping ambiguity. Not helpful. `st7789_lcd`? uses `out pins`. `hub75`? `vdg`? Hmm. pico-examples `pio/pwm`? no. OK here's another authoritative memory: RP2040 datasheet, "3.5.3. ... side-set" — I recall the phrase: "**the side-set base pin, and the side-set count, are configured in the same way as the other pin groups**" and "Side-set is a simple... e.g. to generate a clock... The **MSB** of the side-set value is applied to the **lowest** pin"? Honestly, I now recall reading discussions: side-set bit order — the side-set field, e.g. `.side_set 2`, `side 0b10`: bit 1 (value's bit1) goes to sideset base+1?? and bit0 to base? The natural expectation: sideset value is treated like a number written to the pin group LSB→base pin. Hmm, but there's a twist: pioasm documentation says: "side_set: ... The side-set value is shifted into the pins... **The side-set field is right-aligned**: e.g. with 2 side-set pins, `side 3` sets both pins high." Right-aligned means LSB of value → base pin. I'll go with LSB→base. Let me cross-check with the actual audio_i2s.pio from pico-extras, which I'll now reconstruct from strong memory of having read it: ```pio ; ----------------------------------------------------------- # ; NOTE: # ; ... 16 bit stereo # ; ----------------------------------------------------------- # .program i2s_out .side_set 2 ; ┌──────────┐ ┌──────────┐ ; DATA ─┘ └───────────┘ └─ ; ... ; ┌──┐ ┌──┐ ┌──┐ ; BCK ──┘ └────────┘ └────────┘ └─── ; ──────────┐ ┌───────── ; LRCK └────────────┘ ; Pin assignments: ; 0: DATA ; 1: BCK ; 2: LRCK (BCK + 1) start: set x, 14 side 0b01 data0: out pins, 1 side 0b00 jmp x-- data0 side 0b01 out pins, 1 side 0b10 set x, 14 side 0b11 data1: out pins, 1 side 0b10 jmp x-- data1 side 0b11 jmp start side 0b00 ``` Hmm wait, that gives sideset base = pin 1 (BCK), sideset bit0→BCK, bit1→LRCK. Let's sanity-check this program assuming LSB→base: Define sideset value bit0 = BCK, bit1 = LRCK. - `start: set x, 14 side 0b01` → BCK=0, LRCK=1. - `data0: out pins, 1 side 0b00` → BCK=0 LRCK=0: LRCK falls (channel change), and data bit0 (MSB of left?) driven while BCK low. Hmm wait, LRCK just fell at the same time as first data bit — in I2S, MSB appears one BCK after WS change. Close enough for most DACs? Actually in standard I2S the first data bit should be output starting one clock after WS edge. This program outputs MSB immediately at WS change. MAX98357A (common I2S amp) — tolerant? Probably still works since data is sampled on BCK rising edge and WS transitions... Many hobby implementations do exactly this and MAX98357A works. PCM5102 works too generally. Continue trace (left channel = LRCK low? Here LRCK low occurs during the 16 outs of data0? Let's trace): Instruction timing (1 cycle each): 1. `set x,14` side 01: BCK=0,LRCK=1 2. `out pins,1` side 00: BCK=0,LRCK=0 ← LRCK falls now; DIN=bit15 (MSB) set. 3. `jmp x-- data0` side 01: BCK rises → DAC latches bit15 while LRCK=0. x=14→13? Wait set x,14 then loop with jmp x-- executes 15 times? `jmp x-- data0` decrements and jumps if nonzero: starts x=14, loops while x≠0 after decrement: 14 decrements → loops 14 times? `jmp x-- data0`: if x-- != 0 jump. So with x=14: iterations: 14? Let's count: loop body = [out (2), jmp (3)]. Each jmp decrements x and jumps if result nonzero. Starting x=14: jmp executes with x=14→13 jump, ... continues until x=1→0 no jump. So jmp executes 14 times total, out executes 14 times inside loop + 1 before? Sequence: out(1), [jmp→out]×? Let me linearize: Cycle 2: out (bit15) [side 00: BCK low] Cycle 3: jmp x-- (side 01: BCK high → latch bit15) x:14→13, jump to data0 Cycle 4: out (bit14) side 00 → BCK low, data changes on falling edge ✓ Cycle 5: jmp x-- side 01 → BCK high, latch bit14. x=12 ... pattern continues. x starts 14; jmp decrements: after cycle 5 x=12... wait cycle 3: x 14→13; cycle5: 13→12; ... The loop `out,jmp` repeats: how many times? jmp jumps while x≠0 after decrement. Decrements: 14→13 (c3), 13→12 (c5), ..., 1→0 (c?) — jump fails when x becomes 0. Number of successful jumps = 13 (values 13..1). So out executes: cycle2 (pre) + after each successful jump: 13 more times? Total outs in loop region: 1+13 = 14? Bits latched: bit15 at c3, then each subsequent out followed by jmp latch: bits 14..1 latched at BCK highs = 14 more? Let me recount: Sequence: c2 out bit15, c3 jmp latch bit15 (x=13). c4 out bit14, c5 jmp latch bit14 (x=12). ... each iteration = out+jmp, latching one bit. Iterations continue while jmp jumps. jmp jumps if x after decrement ≠0. c3: 14→13 jump ✓. c5:13→12 ✓ ... The k-th jmp: x = 14-(k)... k-th jmp (k=1..): before decrement x=14-(k-1)? c3 is k=1: x was 14, →13, jump. So jmp #k jumps iff 14-(k-1)-1 = 14-k ≠ 0 → k≤13 jump; k=14: x: 14→? k=14: x was 1 → 0, no jump. So 13 jumps + final no-jump. Outs: c2 out (bit15), then iterations k=1..13: each has out before jmp? No wait, structure: `data0: out pins,1 side 00 / jmp x-- data0 side 01`. Preceded by `set x,14 side 01` at start... but wait my reconstructed program: after `start: set x,14 side 0b01`, `data0: out pins,1 side 0b00; jmp x-- data0 side 0b01`. Hmm but then the FIRST out (c2) is bit15 with side 00 → LRCK falls HERE (side 01 → 00 change: LRCK 1→0). Hmm, actually LRCK was set high at `start` (side 01) — meaning previous frame ended with LRCK high (right channel), now falling → left channel starts. Good: bit15 (MSB of left 16-bit word) appears simultaneously with LRCK fall — slightly non-standard (standard: one BCK later) but works with many DACs. Count bits latched per channel: outs executed while in data0 region: c2 (bit15), c4 (bit14)... Each out is followed by a jmp that latches it. Jmps: c3, c5, ..., until x=0. x=14 initially. jmp at c(2m+1), m=1,2,...: decrements 14→13 at m=1. Jump continues while 14-m ≠ 0, i.e., m ≤ 13 jumps; at m=14 (x 1→0) no jump. So total out+jmp pairs = 14 (m=1..14): 14 outs? outs at c(2m): m=1..14 → 14 outs: bits 15,14,...,2. Then after final jmp fails (c(29), x=0), fall through to `out pins,1 side 0b10` (c30): BCK=0? side 0b10: bit0(BCK)=0, bit1(LRCK)=1 → LRCK rises! And out drives bit1? Wait side 0b10 = value 2: bit0=0 (BCK low), bit1=1 (LRCK high). Hmm: LRCK rises and bit... this out pulls bit1 of left word? Hmm that doesn't seem right either — let me recount: 16 bits per channel need 16 outs+16 latches. We have: 14 outs in loop (bits 15..2), then `out side 0b10` = 15th out (bit 1) with LRCK rising, then `set x,14 side 0b11` = BCK high → latch bit1 (BCK=1, LRCK=1). Then data1 loop: `out side 0b10` 16th out (bit 0) with BCK low... wait side 0b10 → BCK=0, LRCK=1: bit 0 driven, then `jmp x-- data1 side 0b11` → BCK high latch bit0. Loop 14 times → latches bits 0,...? Hold on, bit budget: 16 bits per word; loop structure: set x,14 → 15 iterations? Hmm my count above said 14 outs from 15 jmp-decrements... I think I miscounted: `set x, 14` then loop with `jmp x--`: the loop body executes until x reaches 0: number of `out` executions in data0 region = 15? Let me recount simply: standard pattern "set x,14; loop: out; jmp x-- loop" gives 15 outs (x=14→0: decrements 14 times? no...). x=14. Iteration 1: out, jmp: x=13. Iter 2: x=12... Iter 14: x=0 → jmp fails. So iterations 1..14 execute out; iteration 15: out executes (iter 15? no!). Careful: sequence per iteration: `out` then `jmp x--`. jmp decrements then tests. Iteration i: out; jmp: x goes from 14-(i-1) to 14-i; jumps if 14-i ≠ 0. Jump succeeds for i where 14-i≠0 → i=1..13 jump; i=14: x 1→0, no jump. So outs executed: i=1..14 → 14 outs (plus the pre-loop? there is no pre-loop out; `start: set` then label data0: out...). So 14 outs in data0 region: bits 15..2 (14 bits). Then `out pins,1 side 0b10`: 15th bit (bit 1), with side 0b10 meaning BCK=0,LRCK=1: LRCK rises. Then `set x,14 side 0b11`: BCK=1 LRCK=1 → latch bit1 while LRCK=1 (right channel starting). Hmm — so bit1 of LEFT word is latched during LRCK high?? That's wrong-ish. Then data1 loop: out side 0b10 (BCK low, LRCK high) — 14 outs: bits 0, and 13 more bits from... but the right word's bits! The 16th out in data1 region would be bit0 of left? Wait no: total 16 outs per frame-half needed; we have 14 (bits15..2) + 1 (bit1) = 15 outs with LRCK low→? Hmm bit order: OSR shifts LSB first (default `out shift right`? default shift direction for out is LSB-first? PIO default: shift right = LSB first). Ugh, my reconstruction is suspect. I clearly don't remember the example exactly. ABANDON recall; let me carefully DESIGN one and verify it myself, and choose parameters so that either sideset mapping works? Or determine sideset mapping definitively. Let me settle sideset mapping definitively via logic: The pico-extras `audio_i2s` definitely works on real hardware (widely used). Its pio (I found a copy in my memory from pico-extras/src/audio_i2s/audio_i2s.pio): ``` .program i2s_out .side_set 2 ; ┌───────────────┐ ┌────── ; DATA ┘ └───────────┘ ; (16 bits per channel...) ; ; Pin config: ; 0: data ; 1: bit clock ; 2: LR clock ; ; Note: 2 side-set pins: bit clock and LR clock, so side-set base = 1 ``` and: ``` start: set x, 14 side 0b11 ; ? ``` No... GRRR. Different approach to eliminate ambiguity: use `.side_set 2` but define side values as full 2-bit patterns and assign pins so that BOTH interpretations yield correct I2S? Consider mapping where sideset pins are {BCK, LRCK}. If value v: interpretation A: bit0→BCKbase(BCK), bit1→LRCK; interpretation B: bit0→base+1(LRCK), bit1→BCK. If I only ever use side values where bit0 = bit1 (i.e., 0b00 and 0b11), both interpretations coincide! Can I generate I2S using only side values 0b00 and 0b11? side 0b00: BCK=0,LRCK=0; side 0b11: BCK=1,LRCK=1. That's not I2S (LRCK must be 32× slower than BCK). No good. Alternative: use TWO side-set... no. Use explicit `set pins` for LRCK changes only (twice per frame) and sideset 1 bit for BCK. Then: - sideset 1 pin: base = BCK. side 0 = BCK low, side 1 = BCK high. Unambiguous! - SET pin group: base = LRCK, width 1: `set pins, 0/1` → LSB→base pin. For 1 pin, `set pins, 1` sets it high — unambiguous. - OUT pin group: base = DIN, width 1 — unambiguous. This removes all multi-bit mapping ambiguity. Now design the frame: 16 bits per channel, MSB first. Default OUT shift: for the OSR, `shiftsel`... default shift direction: OUT shifts from LSB? PIO default for both shift registers: shift right (LSB first)?? Actually PIO defaults: `shift_autopull` off etc. For OUT, default shift direction is right (i.e., LSB comes out first)? Hmm: In the SDK, `sm_config_set_out_shift(&c, false, false, 32)`: parameters (shift_right? no: `shift_out_right`?). The function: `sm_config_set_out_shift(c, bool shift_right? ...)`. Hmm: signature: `static void sm_config_set_out_shift(pio_sm_config *c, bool shift_right, bool autopull, uint pull_threshold)`. Hmm wait I think it's `bool shift_right` meaning shift towards LSB... Let me recall: `sm_config_set_out_shift(&c, false, false, 32)` in uart example? UART tx: `out pins, 1` repeatedly, start bit + LSB-first data (UART is LSB first!). uart_tx.pio: uses `out pins, 1` in a loop 8 times; UART sends LSB first; the default config in `uart_tx_program_get_default_config` — does it set out shift? I believe uart_tx uses default shift right (LSB first) which matches UART LSB-first. Yes! Default: shift right (LSB-first) for OUT, threshold 32, autopull false. I2S needs MSB first → configure `sm_config_set_out_shift(&c, true, true, 32)`? wait `shift_right=true` means LSB first. MSB first = shift left = `shift_right = false`... Hmm careful: If shift_right = true, OSR shifts right each `out`, meaning bits exit from LSB side → LSB first. For MSB first we need shift left: shift_right = false. But then autopull refills OSR from MSB side — fine with 32-bit threshold. Actually for I2S, simplest: keep shift right (LSB first) and pre-swap bytes in software! Many implementations just feed the 16-bit sample as (sample << 16 | sample) with bit-reversal... messy. Cleaner: set out shift left with autopull 32 → OSR MSB comes out first. Hmm wait, but there's a subtlety: with shift_right=false (shift left), `out pins, 1` outputs OSR bit31 each time, shifting left. Autopull at 32 refills. Good. But hold on — I want to double-check `sm_config_set_out_shift` parameter semantics: `sm_config_set_out_shift(pio_sm_config *c, bool shift_right, bool autopull, uint pull_threshold)`. Yes, I'm confident that's the signature. shift_right=true → LSB first. So use shift_right=false, autopull=true, threshold=32. Now the PIO program with sideset 1 (BCK), set pins for LRCK, out pins for DIN: ``` .program i2s_out .side_set 1 start: set pins, 0 side 0 ; LRCK = 0 (left) set x, 15 side 0 left_loop: out pins, 1 side 0 ; set DIN while BCK low jmp x-- left_loop side 1 ; BCK high → latch out pins, 1 side 0 ; 16th bit? ``` Hmm wait, need 16 outs. Let me structure: `set x, 15` then loop 16 times: pattern "set x,N; loop: out; jmp x-- loop" executes out N+1 times (x=15 → outs: iterations while jump taken...). Let me count pattern `set x,15 / L: out / jmp x-- L`: jmp decrements from 15: jumps succeed for results 14,13,...,1 → 14 jumps? x=15: jmp1: 15→14 jump ✓ (1 out done before it), ... jmp k: 15→... k-th jmp decrements to 16-k; jumps if ≠0 → k=1..15 succeed (values 14..0? no: 16-k≠0 → k≤15... 16-15=1≠0 ✓ jump; k=16: 16-16=0 no). So outs = 16? Sequence: out, jmp(→14... wait k-th jmp result = 16-k). k=1: result 15? No: x=15, first jmp: 15-1=14? Hmm "jmp x--" decrements x then jumps if nonzero: result of first = 14. Jump iff result≠0: first 14 jmps succeed (results 14..1), 15th: 15→0? x sequence: 15 (set), jmp#1→14, jmp#2→13, ..., jmp#14→1, jmp#15→0 no jump. Outs: out#1..out#15 each followed by jmp; out#16? After jmp#14 jumps back, out#15 executes, jmp#15 fails → exit. So outs executed = 15. Hmm: total outs = 15, not 16. To get 16 outs: `set x, 16`? jmp results: 16→15... jmp#16→0. Outs = 16. Yes: `set x, 16` gives 16 loop iterations? Let me recount with x=16: iteration i: out, jmp: x 17-i → after jmp x=16-i; jumps while 16-i≠0 → i=1..15 jump; i=16: jmp fails. Outs executed: 16. ✓. Hmm wait: but then the LAST out (16th) is followed by jmp that fails — jmp still executes (and latches via side 1!) — good, jmp executes regardless, just doesn't jump. So the 16th bit gets latched. Alternatively use the classic pattern from pico-examples audio: they use `set x,14` with an extra `out` before the loop... whatever, my pattern: `set x,16; L: out; jmp x-- L` → exactly 16 outs and 16 latch edges. Hmm wait — but each `out` outputs ONE bit and each `jmp x--` latches it. But hold on: each out is followed by jmp side 1 (BCK high). But between channels I need LRCK change aligned with a BCK low phase. Full frame design (BCK idles low between bits): ``` start: set pins, 1 side 0 ; LRCK=1 (right) — leftover from previous? ``` Hmm, let's define: left channel transmitted while LRCK=0? Or 1? Philips I2S: WS low = left, WS high = right. DAC doesn't care about which as long as consistent; stereo order: first-left-then-right or vice versa. Let's say: LRCK=0 → LEFT, LRCK=1 → RIGHT. Frame sequence: 1. LRCK goes 0 (left starts). (LRCK changes while BCK low.) 2. 16 bits of left: (out bit while BCK low; BCK high latch) ×16. 3. LRCK goes 1 (right starts), BCK still low. 4. 16 bits right similarly. 5. Repeat. But note: between step 2's last latch (BCK high) and step 3, BCK must go low (side 0) before/at LRCK change. Since `set pins, 1 side 0` executes after the 16th jmp (side 1): one cycle BCK low with LRCK change. But wait — there's a data-availability subtlety: the OSR autopull: 32-bit frames? Each frame = 32 bits (16L+16R). If I feed 32-bit words with (left<<16)|right (MSB first: left in top half), autopull pulls one 32-bit word per frame exactly if OSR empties exactly at frame end. With shift left, threshold 32: after 32 `out,1`, OSR is empty → autopull refills at the next `out`? Autopull happens when shift counter hits threshold — the refill occurs before/when the `out` executes that needs data. With shift-left and pull_threshold=32: after 32 shifts OSR is empty; the next `out` triggers a pull (stalling if FIFO empty). Fine: FIFO with DMA keeps it fed. Hmm, but actually autopull in shift-left mode: the "shift counter" counts shifts; when it reaches threshold, pull happens on the *next*... it happens automatically when `out` would underflow. The mechanics: with autopull enabled, a pull is performed when the OSR shift counter reaches the autopull threshold... The refill occurs at the out instruction that crosses the boundary — meaning the 33rd bit output would stall until new data. Since each frame is exactly 32 bits, the 33rd out is the first bit of the next frame → correct alignment maintained automatically. So PIO program: ``` .program i2s_out .side_set 1 top: set pins, 0 side 0 ; LRCK = 0 → left channel set x, 16 side 0 lbit: out pins, 1 side 0 ; present bit (BCK low) jmp x-- lbit side 1 ; BCK high: DAC latches set pins, 1 side 0 ; LRCK = 1 → right channel set x, 16 side 0 rbit: out pins, 1 side 0 jmp x-- rbit side 1 jmp top side 0 ; hmm: adds a cycle with BCK low, LRCK=1 then set pins 0 side 0 next ``` Wait — issue: `jmp top side 0` then `set pins,0 side 0`: after last right bit latched (side 1), jmp top executes side 0 (BCK low, LRCK still 1), then set pins,0 side 0 (LRCK→0). So there are 2 extra BCK-low cycles per frame — fine (BCK duty/extra low periods don't matter; DACs latch on rising edge). Also note: `set x, 16` — SET instruction operand is 5 bits (0-31), 16 fine. Also `set pins, 0` — SET pin group width: we configure SET pin base = LRCK pin, count 1. `set pins, 0` writes 0 to that pin. Hmm wait, one more check on `out pins, 1` with shift-left: outputs OSR[31], shifts OSR left by 1. Yes. Clock divider: SM clock = sys_clk / div. Bit rate: each bit = 2 cycles (out+jmp). 32 bits/frame → 64 cycles + overhead (set pins, set x, jmp top: +4?) Let me count cycles per frame: set pins(1) + set x(1) + 16×2 + set pins(1) + set x(1) + 16×2 + jmp(1) = 1+1+32+1+1+32+1 = 70 cycles/frame. Sample rate = SMclk/70. For 48kHz: SMclk = 3.36 MHz. sys_clk 150MHz (RP2350 supports 150MHz; default SDK 150MHz? Pico2 default is 150 MHz). div = 150e6/3.36e6 ≈ 44.64. Use 44.64? Divider supports fractional (8.8). Fine. Or choose nice numbers: 44100? Let's pick 48kHz: divider = 150000000/(48000*70) = 44.642857. `pio_sm_set_clkdiv` with float. That yields BCK = 48000×32 = 1.536 MHz, fine for any I2S DAC. Hmm, but actually — wait, is the extra-low BCK period between channels OK per I2S spec? Spec wants BCK continuous, but virtually all DACs (MAX98357A, PCM5102) handle small gaps fine. Accept. Alternatively, cleaner classic approach used by many: sideset for BCK toggle via `jmp` variants... my design is fine. Now — DMA: wire a DMA channel to the PIO SM TX FIFO, reading from a ring buffer or a continuous buffer in RAM. For a synth, best: generate audio in a callback: DMA chain with two buffers ping-pong, interrupt on completion, refill. Or simpler: use two DMA channels chained, each transferring N samples from a static buffer; on completion IRQ recompute the buffer. Simplest robust: single DMA in ring mode? RP2350 DMA supports ring wrap on write address... The DMA can wrap read address? `dma_sniffer`... RP2040 DMA ring applies to WRITE address only. So use two-channel ping-pong or interrupt-per-block with a single channel re-triggered. Easiest reliable: DMA channel with IRQ on block complete; in IRQ handler: restart transfer from same buffer after refilling? Risky timing. Better classic pattern: two buffers, chain channel A → B → A via trigger chaining (`channel_set_chain_to`), each channel's transfer size = buffer; on each channel's completion IRQ, refill THAT buffer with next audio block. This is standard and robust. Actually even simpler and quite robust: use ONE DMA channel in normal mode, with `dma_channel_set_irq0_enabled`, and in the ISR immediately restart `dma_channel_set_read_addr` + `start` — since the PIO FIFO has some slack (4-deep? RP2350 PIO FIFO depth 4? RP2040 FIFOs are 4 deep; RP2350 also 4 deep, 8 with... RP2350 has 8-deep option? RP2350 PIO has 4-deep FIFOs standard? I think RP2350 supports "FIFO join" and maybe 8 deep? RP2040: 4 deep. RP2350: 4 deep too, but there's a 2x "double" ... not sure. Assume 4.) With 48kHz stereo 16-bit, one 32-bit word = 1/48k s = 20.8µs; FIFO 4 words = 83µs of slack; ISR restart latency ~ microseconds — fine. But safer: ping-pong 2 buffers. I'll do ping-pong with chained DMA channels — standard pico pattern. Now the SYNTH — the creative part. Requirements: "novel creative code", "creates a synthesizer when passed to I2S", "generate the sound in a creative way", "allow for user interaction." Creative synth ideas: 1. **Chaos/physical-modeling**: Karplus-Strong plucked string via DMA... no, via software on a buffer — user "plucks" strings by pressing buttons; string = feedback delay with lowpass; novel extension: two strings cross-coupled (sympathetic resonance!), non-linearities. 2. **Fractal/matrix synth**: sound from iterating the logistic map / Mandelbrot escape values, user controls parameters (r, seed) — "sonification of chaos." 3. **Quantum-ish / strange attractor**: integrate Lorenz or Rössler attractor in fixed point; sonify x,y,z as FM modulators; user changes sigma/rho/beta via knobs → "attractor drone synth." 4. **Vocal tract / formant** synth with pots controlling formant frequencies. 5. **Game-of-Life sequencer**: 8×8 cellular automaton grid → step sequencer notes; speed knob; interaction by seeding. The most "synthesizer" feel with genuine novelty: combine several: a **chaotic attractor drone** + **Karplus-Strong pluck pads** + pitch shifting via ADC knobs (Pico 2 has no onboard ADC knobs unless wired to GP26-28... Pico 2 has ADC on 4 pins? RP2350: 4 ADC channels? RP2350 has 4-channel 12-bit ADC (GP26-GP29?) — Pico 2 board exposes ADC0-3? Pico 2: 4 ADC pins? The Pico 2 has 4 ADC channels? Pico 2 has ADC with 4 channels? Pico 1 had 4 (GP26-29); Pico 2: RP2350 ADC = 4 channels? I believe RP2350 has a 4-input 12-bit ADC. Yes — Pico 2 exposes 4 ADC channels (ADC0..ADC3, GP26..GP29). Hmm, actually I recall Pico 2 has only 3 ADC + temp? No... RP2350 datasheet: "4-channel 12-bit ADC". Pico 2 board: ADC0-A? The Pico 2 pinout: GP26=ADC0, GP27=ADC1, GP28=ADC2, and ADC3 = ? On Pico 1, ADC3 = GPIO29 and there's also a 4th... On Pico 2, GP29=ADC3. So 4 channels. Good — but to keep hardware optional, I'll support: pots on ADC (optional), and BOOTSEL button (always available!) for interaction. BOOTSEL is the universal interaction input on a Pico. Also GPIO buttons optional. Interaction via BOOTSEL is great: everyone has it. Plan: BOOTSEL short press = pluck a note / cycle through modes; hold = change parameter. Also ADC knob if attached. Let me design the synth to be genuinely interesting and self-contained: **"CHAOS DRONE + PLUCK" hybrid synth:** Core: **Lorenz attractor-driven FM drone.** Fixed-point Q16.16 integration at control rate (every N samples, e.g., 128). Lorenz x,y,z → map to FM operator frequencies/modulation depths. Knob (ADC0) sets rho (bifurcation parameter) sweeping through chaotic regimes → timbre morphs from dull periodic to wild chaotic. Button adds events. Plus: **Karplus-Strong plucks** on button press — pick pentatonic notes derived from the attractor state (so melody emerges from chaos!) — "the attractor composes." Plus: **ADC-controlled parameters** (or if no ADC hardware, BOOTSEL cycling parameters, and internal LFO from attractor auto-modulates). Also stereo: pan/width from y coordinate; slight stereo decorrelation. Also **RP2350-specific creativity**: use the second core! Core 0: audio synthesis + DMA. Core 1: user interface / control-rate DSP? Or: core 1 renders "voice" DSP while core 0 handles mixing+DMA. Novel: dual-core with `multicore_fifo` for parameter passing. Also could use the RP2350's `Hazard3`/... keep it C SDK. Also could use **interpolator (divider)** or "SIO divider" for envelope math — too deep. Let me also add a **spectral-ish brightness control via one-pole filters**, and a **soft clipper** for glue. Also **PWM-free, I2S only** — good. Let me think about practical buildability: pins: DIN=GP? Choose: DIN GP18? Common choice: GP9? pico-extras audio example uses: data pin 9? I recall PICO_AUDIO_I2S_DATA_PIN=9? Hmm the default in pico-extras examples: `PIN_DATA 9`? Not sure. I'll pick my own clean pins: DIN=GP16, BCK=GP17, LRCK=GP18? But ADC on 26-28 and BOOTSEL... Any GPIO works for PIO. I'll use GP16/17/18? Hmm wait, but on Pico 2, GP16-19 fine. Actually let me use **DIN=GP15?** Keep simple: GP16=DIN, GP17=BCK, GP18=LRCK. Buttons: optional on GP14 (mode), GP13 (pluck). ADC: GP26 (ADC0) knob for chaos amount. Note in comments. Wait, also need to double check PIO instruction `set pins, 0` — SET pin group: must configure `sm_config_set_set_pins(&c, LRCK_PIN, 1)`. And `set x, 16` fine (≤31). `jmp x-- label` — encoding JMP X--: condition 5? JMP with X-- condition is "010" (X-- : jump if X nonzero after decrement). Yes `jmp x-- label` valid pioasm. Sideset 1 pin: `sm_config_set_sideset_pins(&c, BCK_PIN)` and `sm_config_set_sideset(&c, 1, false, false)`? The config function: `sm_config_set_sideset(pio_sm_config *c, uint bit_count, bool optional, bool pindirs)`. Since every instruction in my program uses a side value? Not all — wait, ALL instructions need side fields? If some instructions lack `side`, with non-optional sideset, they're encoded with side 0. In my program: `set pins,0 side 0` etc. Every instruction has explicit `side 0` or `side 1`? Let me ensure: in the loop `out pins, 1 side 0` and `jmp x-- lbit side 1` — I'll write sides on all instructions explicitly. With sideset non-optional (bit_count=1, optional=false), every instruction's side field defaults to 0 if unspecified — but JMP-side1 lines specify. I'll write them explicitly everywhere for clarity. Also must set pin directions: `pio_sm_set_consecutive_pindirs` or in config: `sm_config_set_out_pin... ` The SDK: after init: `pio_sm_config c`; set `pio_set...`. Typical pattern: ```c pio_gpio_init(pio, PIN_DIN); pio_gpio_init(pio, PIN_BCK); pio_gpio_init(pio, PIN_LRCK); pio_sm_config c = i2s_out_program_get_default_config(offset); sm_config_set_out_shift(&c, false, true, 32); // shift left (MSB first), autopull 32 sm_config_set_out_pins(&c, PIN_DIN, 1); sm_config_set_sideset(&c, 1, false, false); sm_config_set_sideset_pins(&c, PIN_BCK); sm_config_set_set_pins(&c, PIN_LRCK, 1); sm_config_set_fifo_join(&c, PIO_SM_FIFO_JOIN_TX); // RP2350? available? RP2040 yes. pio_sm_set_consecutive_pindirs(pio, sm, PIN_DIN, 3, true); // wait LRCK pin not consecutive with DIN/BCK? DIN=16,BCK=17,LRCK=18 consecutive! sm_config_set_clkdiv(&c, div); pio_sm_init(pio, sm, offset, &c); pio_sm_set_enabled(pio, sm, true); ``` Choose pins consecutive: DIN=GP16, BCK=GP17, LRCK=GP18 → `pio_sm_set_consecutive_pindirs(pio, sm, 16, 3, true)` sets all as outputs; also `sm_config_set_...` fine. Wait: sideset pin BCK=17, set pin LRCK=18, out pin DIN=16 — groups can overlap? They're distinct pins, fine. pio_gpio_init for each of 16,17,18. Now sample generation: Main structure: - Buffers: two stereo buffers of, say, 64 frames each (64 × 32-bit words). int32_t buf[2][64]. - Two DMA channels ch0, ch1 chained: ch0 transfers 64 words from buf[0], chain_to ch1; ch1 transfers from buf[1], chain_to ch0. IRQ on each completion: recompute that buffer. - ISR: `dma_acknowledge_channel0_irq... ` For RP2350 SDK: `dma_channel_acknowledge_irq0(ch)`, `dma_channel_set_irq0_enabled(ch, true)`. Wait, chaining semantics: when ch0 finishes it triggers ch1 (which starts transferring buf[1]); meanwhile ISR refills buf[0]. When ch1 finishes → triggers ch0 (re-read from buf[0] — read addr must be reset!). Chained restart reuses the SAME configured read address — since each channel always reads the same buffer, we just set read_addr once per channel and chain restarts reuse it. - IRQ handler on ch0 completion: refill buf[0]; on ch1 completion: refill buf[1]. Timing check: 64 frames @48k = 1.33ms per buffer — ISR each 1.33ms; render cost must fit; synth at 48k mono-ish per sample with moderate math — RP2350 M33 @150MHz: ~3000 cycles/sample budget; our DSP per sample maybe ~200-400 cycles → fine even with both cores. Now the DSP design (creative core): **A. Lorenz attractor (control-rate, every 128 samples ≈ 375 Hz):** x,y,z Q16.16; params sigma=10, rho (user/automated 1..60), beta=8/3. dt small (e.g., 0.005 Q16: dt=0.005*65536≈328). Update: dx = sigma*(y-x); etc. Multiply Q16.16 via int64 mults. Map: - Carrier freq base: e.g., 55–110 Hz saw-ish (FM). - FM index from |x| normalized; LFO-ish drift from y. - Filter cutoff from z (clamp). - Pan from sign/level of y. **B. Two FM operators:** mod osc → carrier osc; carrier = "sine" via quarter-wave LUT 256-entry Q16. Use LUT of int16 sin. Phase accumulate Q16.16 per-sample increment. Cheap. **C. Karplus-Strong pluck voices (poly 4):** Each voice: delay line length = note period (in samples, e.g., 100–800), feedback = lowpass(y) * decay. On trigger: fill with noise burst or excite with shaped burst; render per sample: read y[n-L] avg with y[n-L-1]? Classic: `buf[i] = 0.5*(buf[i-L]+buf[i-L-1]) * decay`. Implement as circular buffer per voice with pointer. Note choice: pentatonic scale quantized from attractor x — "chaos picks the melody." **D. One-pole lowpass for drone (cutoff from z), simple 4-stage? Keep one-pole LP + HP to remove DC. **E. Soft clip tanh-ish: y = y*(27+y²)/(27+9y²)? Use cubic soft clip rational approx — cheap: `x - x*x*x/(...)`. Or use `tanh` via repeated... use simple: clip via x/(1+|x|/3)? Fine: s = x/(K+|x|) style. **F. Stereo: plucks panned alternately; drone panned by y. Also maybe a **"breath" noise** with bandpass following rho. Interaction: - BOOTSEL: press → pluck a note (queue event flag; also used to re-seed attractor if double-click?). Simple: each press = pluck; long press (>800ms) = cycle "rho" lock/scan mode. - Optional buttons on GP13/GP14: pluck / param. - ADC knob GP26: sets rho (chaos→timbre). ADC via `adc_select_input(0)`, read in core1 loop. - UART console prints state (optional; keep prints minimal, off the audio path). Second core usage: core1 handles UI (button scan, ADC, event generation, parameter smoothing); passes messages via `multicore_fifo` (push note events/param deltas) — nice RP2350 flavor and keeps audio deterministic on core0. Also, RP2350-specific: could mention `set_sys_clk_150mhz?` The Pico 2 default clock is 150MHz. Fine. Now — code specifics. Let me be careful with SDK APIs (C SDK for Pico 2, SDK 2.x): - `#include "pico/stdlib.h"`, `pico/multicore.h`, `hardware/pio.h`, `hardware/dma.h`, `hardware/adc.h`, `hardware/irq.h`, generated header `i2s_out.pio.h`. - CMakeLists: standard pico project with `pico_sdk_init()`, `pico_add_extra_outputs`? For PIO: `pico_generate_pio_header(${PROJECT_NAME} ${CMAKE_CURRENT_LIST_DIR}/i2s_out.pio)`. Provide full CMakeLists. DMA config: ```c dma_channel_config cc = dma_channel_get_default_config(ch0); channel_config_set_transfer_data_size(&cc, DMA_SIZE_32); channel_config_set_read_increment(&cc, true); channel_config_set_write_increment(&cc, false); channel_config_set_dreq(&cc, pio_get_dreq(pio, sm, true)); channel_config_set_chain_to(&cc, ch1); dma_channel_configure(ch0, &cc, &pio->txf[sm], buf[0], N_FRAMES, false); ``` Wait `dma_channel_configure(channel, &config, write_addr, read_addr, transfer_count, trigger)` — signature: `dma_channel_configure(uint channel, const dma_channel_config *config, const volatile void *write_addr, const volatile void *read_addr, uint transfer_count, bool trigger)`. Yes, (ch, cfg, write, read, count, trigger). IRQ: `dma_channel_set_irq0_enabled(ch0, true); dma_channel_set_irq1_enabled(ch1,true)`? Put both on IRQ0: both channels irq0; handler checks `dma_irqn_get_channel_status?` In SDK 2.x: `dma_channel_get_irq0_status(ch)`? There's `dma_channel_acknowledge_irq0(ch)`. For shared handler: ```c void __not_in_flash_func(dma_isr)() { if (dma_channel_get_irq0_status(ch0)) { dma_channel_acknowledge_irq0(ch0); render_block(0); } if (dma_channel_get_irq0_status(ch1)) { dma_channel_acknowledge_irq0(ch1); render_block(1); } } ``` Hmm, does `dma_channel_get_irq0_status` exist in SDK 2.x? I recall `dma_channel_get_irq0_status(uint channel)` added at some point (SDK 1.4+?). There's also reading `dma_hw->intr`. Safer: read `dma_hw->intr` bitmask and clear via `dma_hw->ints0 = bits`? SDK function `dma_channel_acknowledge_irq0` writes the channel bit to `ints0`. I'll use `dma_channel_get_irq0_status` — I'm fairly confident it exists in SDK 2.x (it does: `dma_channel_get_irq0_status` and `dma_channel_get_irq1_status` exist since SDK 1.5). To be extra safe, could use raw `dma_hw->intr`. I'll use the SDK functions; they're standard now. Wait, one gotcha: IRQ handler runs while channel has already re-triggered its chained partner; refill timing: after ch0 completes, ch1 starts immediately (chain trigger). We have whole 1.33ms to refill buf[0]. Fine. Also `irq_set_exclusive_handler(DMA_IRQ_0, isr); irq_set_enabled(DMA_IRQ_0, true);` DMA channel claim: `dma_claim_mask`? Just `dma_claim_channel`? use `dma_claim_unused_channel(true)` twice; get their numbers; configure chain. But chain_to needs both numbers first — fine. Multicore FIFO: `multicore_fifo_push_blocking` / `multicore_fifo_pop_blocking`. Message encoding: 32-bit word: low 16 = note freq or 0xFFFF; top bits = msg type. Core1 pushes events; core0 drains in render block start (control-rate tick). Non-blocking-ish: core0 pops with `multicore_fifo_pop_status()`? There is `multicore_fifo_pop()` (non-blocking returns whatever?) — safer: check `multicore_fifo_rcv_ready?` Hmm API: `multicore_fifo_pop_blocking()`, `multicore_fifo_push_blocking()`, and `multicore_fifo_pop_timeout_us?` Simple: core1 pushes rarely (events); core0 at each block render: `while (multicore_fifo_rdy())`? The status function: `multicore_fifo_pop_status()`? I don't remember exact name. Alternative simpler: shared volatile event mailbox with atomic-ish flag + spinlock? Simplest reliable: a volatile struct with a `pending` flag; core1 writes event, sets flag; core0 polls/clears. Single 32-bit mailbox: `volatile uint32_t g_event;` core1: `g_event = msg;` core0: read & clear. Race: overwritten events just coalesce — acceptable. Avoid multicore FIFO API riskiness. Actually multicore_fifo functions are stable and I'm confident: `multicore_fifo_push_blocking(uint32_t)`, `multicore_fifo_pop_blocking()`, `multicore_fifo_push_status()`/`multicore_fifo_pop_status()`? Hmm "multicore_fifo_pop_timeout_us"... I'll just use the simple volatile mailbox — bulletproof and easy to read. Use `__dmb()`? For simplicity volatile suffices practically. BOOTSEL reading: `get_bootsel_button()` — actually function is `bool get_bootsel_button(void)`? In SDK: `pico_bootrom.h` provides `is_bootloader...`? The common snippet: ```c #include "pico/bootrom.h" // or "pico/bootrom.h" has: static inline bool get_bootsel_button() { return !(stdio_usb?...) } ``` Standard trick used in examples: ```c #include "pico/bootrom.h" bool __bootsel_button() { rom_func_lookup... } ``` Actually known snippet (from Pico forums / SDK examples): ```c #include "pico/bootrom.h" #define BOOTSEL_BUTTON 1? no... ``` The well-known code: ```c static inline bool get_bootsel_button(void) { return !((*(volatile uint32_t*)IO_QSPI_HW_GPIO_QSPI_GPIO_CS_CTRL?) & ...) } ``` Hmm: The BOOTSEL button on Pico pulls QSPI CS (GPIO1 of QSPI, i.e., `IO_QSPI` bank pin 1) low. Known snippet: ```c #include "pico/bootrom.h" // not needed actually #define QSPI_CTRL_REG (*((volatile uint32_t *)(IO_QSPI_BASE + IO_QSPI_GPIO_QSPI_CS_CTRL_OFFSET? ))) ``` The canonical snippet (widely circulated, from `pico-extras`? from "bootsel_button" example by kilograham): ```c static inline bool get_bootsel_button(void) { // QSPI CSn is GPIO1 of qspi bank uint32_t flags = save_and_disable_interrupts(); rom_connect_internal...? ``` No no. The actual widely-used snippet: ```c #include "hardware/regs/io_qspi.h" #include "hardware/structs/io_qspi.h"? bool get_bootsel_button() { // set CS high input? } ``` I remember the exact one from the forums: ```c static bool __noinline get_bootsel_button(void) { // Get current state of QSPI CS pin gpio_set_input_enabled?? } ``` Hmm — here's the actual known implementation (from Raspberry Pi forums / used in many projects): ```c #include "pico/bootrom.h" #define BOOTSEL_BUTTON_GPIO 1 // QSPI bank static inline bool get_bootsel_button(void) { // Configure QSPI CS as input with pull-up, read, then restore ... } ``` The precise trick: ```c static bool get_bootsel_button() { // from https://github.com/.../bootsel uint32_t tmp = *(volatile uint32_t*)((IO_QSPI_BASE) + 0x18? ); ``` Hmm. IO_QSPI GPIO1 (QSPI CS) control register: `IO_QSPI_GPIO_QSPI_CS_CTRL` offset 0x18? IO_QSPI GPIO base 0x40030000; GPIO_QSPI_CS_CTRL at offset 0x0? For bank io_qspi: GPIO0 = SD? no wait IO_QSPI pins: 0=SD0? QSPI: SD0..SD3 = IO_QSPI GPIO 0? Actually IO_QSPI bank: GPIO0=SD0? No: IO_QSPI: GPIO0 = SD0? Hmm the QSPI: six signals: SS(CS), CLK, SD0-SD3. IO_QSPI GPIO numbering: 0 = SD0? 1 = CS? I recall CS = IO_QSPI GPIO 1. Yes (that's why the trick reads pin 1). The forum snippet: ```c static inline bool get_bootsel_button(void) { const uint32_t CS_CTRL = IO_QSPI_BASE + 0x00000018? ``` I actually remember the snippet from "pico-boot-button" projects: ```c bool get_bootsel_button(void) { // QSPI_SS is GPIO 1 in the QSPI bank volatile uint32_t *reg = (volatile uint32_t *)(IO_QSPI_BASE + 0x18); // GPIO_QSPI_CS_CTRL? ``` Hmm IO_QSPI GPIO_QSPI_CS_CTRL: offsets in io_qspi: GPIO_QSPI_SCLK_CTRL=0x08? Per RP2040 register map: IO_BANK0 at 0x40014000; IO_QSPI at 0x40030000. Registers: offset 0x00 = IRQ ctrl? GPIO controls start: GPIO_QSPI_SCLK_CTRL at 0x04? Hmm. The pattern: IO_QSPI: 0x000 IRQ... Actually each GPIO bank: first 0x? = GPIOx_CTRL per pin: For IO_BANK0, GPIO0_CTRL is at offset 0x004? IO_BANK0: 0x000 = ...? IO_BANK0 layout: 0x000-0x00c: INTR etc? I recall GPIO0_CTRL = 0x004? No wait: IO_BANK0_BASE + 0x000 = INTR? Hmm: IO_BANK0: offset 0x000 = INTR? Then GPIO0_CTRL at 0x004?? Not quite: IO_BANK0 GPIO0_CTRL is at offset 0x004? Let me recall: IO_BANK0: 0x000 INTR? no... Structure: `IO_BANK0_PROC0_INTE0` at 0x100? and GPIO0_CTRL at 0x004? Hmm I remember GPIOx_CTRL: GPIO0 at offset 0x004, stride 8? No stride... Each pin CTRL at 0x004 + 8*? For IO_BANK0: GPIO0_CTRL=0x004? GPIO1_CTRL=0x008? ... That doesn't match the known "0x004" + 8*pin? Actually yes: GPIO_CTRL registers are spaced 8 bytes: GPIO0_CTRL at 0x004? Hmm, I recall the bootsel snippet using `0x18` for CS: if SCLK_CTRL=0x08? CS=GPIO1 → 0x08+8*1=0x10? The widely copied snippet (from "bootsel_button" gist by adafruit? used in CircuitPython as supervisor/tick? and in many Arduino cores) is: ```c static bool __noinline get_bootsel_button(void) { const uint32_t CS_PIN_CTRL = IO_QSPI_BASE + 0x18? ``` Hmm honestly I remember: `#define IO_QSPI_REG(a) (...)`. The gist (e.g., https://gist.github.com/... "read bootsel button"): ```c static inline bool bootsel_button(void) { // Pull CS high uint32_t cs = IO_QSPI->hw->io[1].ctrl? ``` CircuitPython's `mpconfigport`... In TinyUSB/pico examples: "bootsel_button": ```c #define PIN_NUM_LED 25 ... static inline void board_button_init... gpio_init? ``` OK here's the definitive one I actually trust — from `pico-extras`? No — from the official `pico-examples`? Not there. It's from kilograham's gist: ```c #include "pico/bootrom.h" static inline bool get_bootsel_button(void) { return (IO_QSPI->hw->io[1].ctrl? ``` Alternatively — simplest & official: `#include "pico/bootrom.h"` doesn't provide it. BUT the ROM function... There IS an official way now: SDK 1.5+ has `get_bootsel_button()`? Hmm, is there? I don't think the SDK exposes it. Given uncertainty, I should implement BOOTSEL reading via direct register access with my own reasoning, OR use `bootsel` via QSPI pin: another approach — RP2040: `gpio_set_function(1, GPIO_IN)`? No—bank is IO_QSPI not IO_BANK0; SDK gpio functions address IO_BANK0 only. Direct regs needed: RP2040 IO_QSPI base 0x40030000. Register offsets (from datasheet Table): - 0x000: IRQ INTE? no wait IO_QSPI starts with IRQ registers like IO_BANK0? IO_BANK0 at 0x40014000: 0x000 INTR... Actually IO_BANK0: 0x000-0x0FC: IRQ setup (INTR 0x000? INTE 0x004..? no that's 4 words... hmm IO_BANK0: PROC0_INTE0 at 0x100), GPIO0_CTRL at 0x004+8*0? Hmm wait I recall GPIO0_CTRL = 0x004? Let me reconstruct: IO_BANK0 registers: 0x000: (unused?), 0x004: GPIO0_CTRL, 0x008: GPIO1_CTRL? That stride-8 pattern gives GPIO29_CTRL at 0x004+8*29=0x0EC; then IRQ regs at 0x0F0+... and PROC0_INTE0 at 0x100. Yes! That matches: PROC0_INTE0 = 0x100 ✓ (I'm confident IO_BANK0_PROC0_INTE0 is offset 0x100). So GPIOx_CTRL = 0x004 + 8x. For IO_QSPI (base 0x40030000): 0x004? The pins there: QSPI SD0? Hmm IO_QSPI has GPIO_QSPI_SCLK_CTRL at... if same stride-8 from 0x004: pin0=SD0? But wait — I recall GPIO_QSPI_SCLK_CTRL at offset 0x08? Hmm. If pin numbering: 0=SD0? no... Let me recall from the bootsel gist — I'm now fairly sure the gist is: ```c static inline bool get_bootsel_button(void) { // read QSPI CS pin (GPIO1 in IO_QSPI bank) ... } ``` RP2040 datasheet Table 310 (IO_QSPI): GPIO_QSPI_SCLK_CTRL at 0x04? GPIO_QSPI_SS_CTRL at 0x08? Hmm. Honestly, rather than risk this, better plan: **don't use BOOTSEL**; use a regular GPIO button (e.g., GP14 to GND, internal pull-up) — bulletproof, and users with a Pico 2 have jumpers... but "allow user interaction" — a plain GPIO button is totally standard and safe. Additionally provide BOOTSEL via the well-known trick but clearly as optional? Actually! I remember now definitively — the widely used snippet (from the official Raspberry Pi forums, by kilograham, copied into countless projects): ```c #include "pico/bootrom.h" static inline void reset_to_bootloader? no. // THIS ONE: bool __noinline get_bootsel_button() { // QSPI SS pin = IO_QSPI bank GPIO 1 ... } ``` The actual code (I'm quite sure of this one, it appears in e.g. usb host examples and many repos): ```c static inline bool get_bootsel_button(void) { return (1u << 1) & ~(* (volatile uint32_t *) (IO_QSPI_BASE + 0x0004? ... ``` Nope. Alternatively adafruit's version: ```c static inline bool __get_bootsel_button(void) { uint32_t cs_ctrl = *((volatile uint32_t *)(IO_QSPI_BASE + 0x18)); // GPIO_QSPI_CS_CTRL? ``` I keep going back and forth. RP2350 also complicates (BOOTSEL on QSPI CS too? On Pico 2, BOOTSEL still shorts SS to GND? Yes). DECISION: Use a GPIO button on GP14 (with internal pull-up) as primary interaction, plus ADC knob, plus UART commands maybe. And ALSO implement BOOTSEL reading — risk is pinning exact offset. Let me pin it down by reasoning about IO_QSPI register layout from the RP2040 datasheet which I partially remember: IO_QSPI base 0x40030000. Datasheet section 2.20? Table: "IO_QSPI: Offset 0x000 IRQ... 0x004 GPIO_QSPI_SCLK_CTRL? ..." Hmm I genuinely recall `GPIO_QSPI_SCLK_CTRL = 0x000? and GPIO_QSPI_SS_CTRL = 0x008?`. Hmm, no wait — I recall from writing RP2040 code: IO_QSPI GPIO_QSPI_SCLK_CTRL = 0x40030004? and CS at 0x40030008? If pins: SCLK=0, SS=1, SD0=2, SD1=3, SD2=4, SD3=5. Then GPIO_QSPI_x_CTRL = 0x004 + 8*pin: SCLK=0x004, SS=0x00C? hmm inconsistent with my memory of 0x08. Let me settle differently: BOOTSEL high-level: The button connects SS (QSPI CS) to GND. To read: set SS pad as input with pull-up disabled? Actually the flash is on the same pin! During runtime you must NOT disturb CS for long; the trick: temporarily switch CS pad function to input (bypassing the SSI), enable pull-up, read, then restore to SSI function quickly with interrupts disabled. The gist: ```c static inline bool get_bootsel_button(void) { // From: https://github.com/raspberrypi/pico-bootrom ... const uint32_t PIN = 1; // SS ... hw_write_masked(...); } ``` I'll write my own version with this structure: ```c #include "hardware/regs/io_qspi.h" // RP2040; RP2350? SDK provides io_qspi.h for both? ``` For SDK 2.x on RP2350, the header `hardware/regs/io_qspi.h` exists (RP2350 has IO_QSPI too). Registers: `IO_QSPI_GPIO_QSPI_CS_CTRL` — I believe that symbol exists. And `IO_QSPI_BASE`? Actually symbol: `IO_QSPI_BASE` from addressmap: `IO_QSPI_BASE _u(0x40030000)` RP2040; RP2350: io_qspi at 0x40028000? RP2350 addresses differ! RP2350 IO_QSPI_BASE = 0x40028000? Hmm: RP2350: IO_BANK0 at 0x40028000? I recall RP2350 map: PADS_QSPI 0x40044000... uncertain. Using SDK macros `IO_QSPI_BASE` and `IO_QSPI_GPIO_QSPI_CS_CTRL` avoids hardcoding — headers define them per-chip. Hmm wait — RP2350 register naming: hardware/regs/io_qspi.h for RP2350 defines `IO_QSPI_GPIO_QSPI_CS_CTRL`? RP2350 IO_QSPI regs named similar: `IO_QSPI_GPIO_QSPI_CS_CTRL` — plausibly identical (SDK kept naming). And the pads: also need PADS_QSPI? To enable pull-up on the CS pad: function select bits FUNCSEL = 5 (GPIO)? Wait the QSPI CS funcsel for raw GPIO... The known gist (now I really do recall it — it's in `bootsel_button` example in some repos, e.g. "pico-bootsel-button"): ```c static inline bool get_bootsel_button(void) { // Get the current state of the QSPI CS pin const uint32_t PINCTRL = IO_QSPI_GPIO_QSPI_CS_CTRL; uint32_t old = *((volatile uint32_t *)PINCTRL); hw_write_masked((volatile uint32_t*)PINCTRL, 1<>16); } ``` σ=10 → Q: 10<<16. β=8/3 ≈ 2.6667 → 174762. ρ variable. step: ```c int32_t dx = mulq(SIGMA, s->y - s->x); int32_t dy = mulq(s->x, RHO - s->z) - s->y; int32_t dz = mulq(s->x, s->y) - mulq(BETA, s->z); s->x += mulq(dx, DT); // dt Q16.16? but DT as Q16.16 times Q16.16 velocity... velocity* dt: dx is Q16.16 * (per unit time). mulq(dx, DT_Q) with DT_Q=262 gives Q16.16 delta. ✓ ``` Mapping to audio: - normalize: xa = x/40 clamp [-1,1]; ya = y/40; za = z/(ρ_max~50) → z01. - Carrier base freq: 60 Hz + 40*|x|/40 → 55..95 Hz? Let carrier base f_c = 50 + 55*(0.5+0.5*sin? ) — keep: f_c = 55 + |x/40|*40 clamp. - FM ratio: mod freq = f_c * (ya-based ratio 0.5..2). - FM index: from (ρ setpoint): 0..8. - Filter cutoff: 300 Hz + 3000*z01. - Pan: 0.25 + 0.5*(ya+1)/2. FM rendering per sample: ```c phase_mod += inc_mod; // Q16.16 phase int32_t pm = sin_q16(phase_mod) * index >> 16; // ±index carrier_phase += inc_c + pm; int32_t s = sin_q16(carrier_phase); ``` sin LUT: 1024-entry int16 covering full circle? 1024 entries int16 = 2KB; index = phase >> 16 & 1023; but sin table needs quadrant logic if table is quarter-wave. Full 1024-point full-period table is simplest: value at i = sin(2π i/1024)*32767 → int16. Memory fine (2KB RAM). Lookup: `int16_t g_sin[1024]`? Fill at startup with double math? Use float sinf in init (fine at boot). `phase` Q16.16 with 1024 table → index = (phase >> 16) & 1023, but Q16.16 phase wraps at 65536 = full period only if we treat phase in units where 65536 = 2π. Yes: phase increments in Q16.16 with 65536 ≡ one cycle. Table index = phase>>16 (0..65535→ /64 → 1024): index = (uint32_t)phase >> 6 & 1023. inc for freq f: inc = f * 65536 / 48000 ≈ f * 1.366 → e.g., 110 Hz → 150. Use precomputed per control tick. Karplus-Strong voice: ```c typedef struct { int16_t d[1024]; // delay line uint16_t len; // period in samples uint16_t pos; int32_t last; // for LP int32_t amp; // envelope Q16? amplitude Q16.16 decaying int32_t decay; // per-period loss Q16 bool active; } voice_t; ``` Render: y = avg of d[pos] and d[pos+? ]... classic: value = (d[p] + d[p+1])/2 * feedback. Implementation: ```c int32_t s = d[pos]; int32_t nxt = d[(pos+1)%len]; int32_t lp = (s + nxt) >> 1; d[pos] = (int16_t)((lp * decay) >> 8)? ``` Standard KS: `buf[i] = decay * 0.5*(buf[i] + buf[i+1])`. decay ~ 0.996 in Q16: 65280? (0.996*65536=65274). Then read head separately. Let me implement: ```c uint32_t p = v->pos; int32_t a = v->d[p], b = v->d[(p+1)%len]; int32_t out = a; // output the current tap v->d[p] = (int16_t)mulq((a+b)>>1, v->decay); // decay Q16.16 ~ 65300 v->pos = (p+1) % len; // wait mod len per sample — use if (++p>=len) p=0; ``` Excitation: on trigger, fill d[0..len-1] with filtered noise: noise burst with brightness: d[i] = (rand & 0x1FFF) - 4096? and lowpass a bit: keep simple: fill with random int16 then one-pass smoothing: d[i] = 0.6*noise + 0.4*d[i-1]? Gives pick-like pluck. Note choice: pentatonic minor scale on A2 (110 Hz): semitone offsets [0,3,5,7,10,12,15,17,19,22,24] over 2 octaves; pick index from attractor: idx = (x>>? ) Use `pick = (uint32_t)(s.x + 50000) >> 8 & 7`? Better: quantize y/40*11 → scale index. This creates melody "composed by the attractor" — nice narrative. Voice count: 4 (4 × 1024 int16 = 8KB) fine (RP2350 has 520KB SRAM). Also add **"chaos shimmer"**: a faint 2nd FM pair? Skip, keep clean. Envelope/amp: drone amplitude from knob? The pot sets rho; also maybe second pot... only using ADC0; buttons handle rest. Per-sample pipeline (48kHz): 1. Update Lorenz-derived params at control ticks (every 128 samples). 2. Per sample: FM drone sample s_d (int32 Q? choose Q: sin LUT int16 amplitude ±32767; carrier s = sin value (int16→int32). FM: pm = (int32)sin(mod)*INDEX>>16 → add to carrier inc: phase += inc + pm). Drone gain g_d (Q16): e.g., 12000? Output O = (drone*s??). Let's define final mix target int16 ±~12000 with headroom, soft clip. 3. Voices: sum 4 KS outputs (int32). 4. One-pole lowpass on drone+voices mix (cutoff from z): `lp += (x - lp) * a >> 16`, a = cutoff coefficient Q16. 5. Stereo: left/right with pan; slight delay on right for width? Add simple: right = mix filtered with different LP coefficient + pan. 6. Soft clip: `y = y*(k) ...` use `s = (x*32767)/(32767+abs(x)*?)`: do scaled soft clip: `int32_t t = x; int32_t y = t - ((t*t*t)>>24)/?` hmm keep simple hard-ish clip with cubic: precompute... Use: `y = t > 0 ? min... ` soft via: `y = (t*14000)/(14000+abs(t))`? multiply+divide per sample ×2 — M33 has hardware divider (fast). Use `SIO div` — plain C division uses hw divider, ~9 cycles. OK. Actually simpler soft clip: `int32_t y = t; if (y > TH) y = TH + (y-TH)>>2; if (y < -TH) ...` piecewise. Cheap. Output stage: convert to int16 pair, pack `(uint32_t)((uint16_t)left | ((uint32_t)(uint16_t)right << 16))` — remember PIO shifts out MSB first: OSR MSB→first bit = left MSB → so left must be in the TOP 16 bits: word = (left<<16)|right. ✓ (with out shift left, MSB first → first 16 bits = bits 31..16 = left → transmitted while LRCK=0 (left) ✓ matches our PIO order: LRCK=0 phase is first half of frame ✓). Render function fills int32_t buf[N] with (L<<16)|R. Performance estimate per sample: FM: 2 sin lookups + muls (~15 cycles each) + KS 4 voices (mod, muls) + filters ≈ maybe 150-250 cycles → at 48k = 12M cycles/s vs 150M — plenty. All in ISR on core0? Put render in main loop core0 instead? DMA IRQ does refill — do rendering in IRQ (blocks are small, 64 frames = 1.33ms @ ~250 cycles/sample*64 = 16k cycles = 107µs — fine). Hmm wait, 64-sample blocks at 48k = 1.33ms per buffer; render 64 samples ~ 16k cycles = 0.11ms — OK. Better: render into the just-completed buffer inside ISR (as planned). Now, the "creative way" summary to present: - "Chaosynth": a **Lorenz-strang drone** (strange attractor = FM drone patch) + **attractor-composed pentatonic plucks** (Karplus-Strong) + pot morphs the bifurcation parameter → from laminar to chaotic timbres. Also, inter-core: core1 does UI: reads buttons, pot, drifts parameters, and triggers plucks; passes events via mailbox. Also add gentle auto-play: if no input for 5s, core1 "ghost plays" occasional plucks chosen by attractor — nice touch ("it plays itself"). Wait — also must handle: `stdio` optional. Buttons debounce on core1. Also mention wiring: I2S DAC modules (MAX98357A / PCM5102 / UDA1334) — give pin table. GP16 DIN, GP17 BCK, GP18 LRCK. Buttons GP13/GP14. Pot ADC0=GP26 (also on Pico 2? GP26 = ADC0 yes). Also CMakeLists.txt and pio file contents — deliver a complete mini-project: `CMakeLists.txt`, `i2s_out.pio`, `chaosynth.c`. Now let me also double-check the DMA chaining + IRQ timing more carefully for the two-channel ping-pong: - ch0 configured: read buf0, write pio txf, count N, chain_to ch1. ch1: read buf1, ..., chain_to ch0. Start: `dma_channel_start(ch0)`? Wait trigger both? Start ch0 only: when ch0 finishes → triggers ch1 → ch1 finishes → triggers ch0 (read addr for ch0 persists). ✓. IRQ0 enabled on both. Handler: refill buffer of the channel that just completed. Note: when ch0 completes and handler refills buf0 — meanwhile ch1 is streaming buf1 (valid data). ✓ No race since refill completes within 1.33ms easily. One more check: `channel_config_set_chain_to(&cc, other)` makes completion trigger `other`. Also need `channel_config_set_enable? ` no. AB-integral? fine. Wait, actually there's a subtle: chained trigger "aborts"? Chain: when a channel completes, it triggers the channel it is chained to — if that channel is not yet started/paused, it starts. Both channels in normal enable state: OK. But initial: ch1 must not start before configured. Configure both, then `dma_channel_start(ch0)`. Also careful: ch0's first block must contain silence/valid audio (we render before start). We'll pre-render both buffers before starting DMA & SM. Also PIO FIFO: txf write via DMA DREQ `pio_get_dreq(pio, sm, true)`. ✓ IRQ setup: `irq_add_shared_handler(DMA_IRQ_0, handler, PICO_SHARED_IRQ_HANDLER_DEFAULT_ORDER)`? or exclusive: only our two channels on IRQ0 — use `irq_set_exclusive_handler(DMA_IRQ_0, isr)` then `irq_set_enabled(DMA_IRQ_0, true)`. Also `dma_channel_set_irq0_enabled(chn, true)` for both. ✓ (SDK 2.x fine.) Hmm — RP2350 has DMA_IRQ_0/1/2/3 (4 IRQs); DMA_IRQ_0 exists ✓. Now the PIO program final check — write it precisely: ``` .program i2s_out .side_set 1 start: set pins, 0 side 0 ; LRCK low -> left set x, 16 side 0 bitloopL: out pins, 1 side 0 ; DIN = next bit, BCK low jmp x-- bitloopL side 1 ; BCK high: DAC samples set pins, 1 side 0 ; LRCK high -> right set x, 16 side 0 bitloopR: out pins, 1 side 0 jmp x-- bitloopR side 1 jmp start side 0 ``` Wait — `set pins, 0` immediately followed by `set x,16 side 0`: 2 cycles BCK low before first bit. Then 16×(out side0, jmp side1): bit presented during BCK low cycle, latched on high. After 16th latch (side 1 on jmp), next instr `set pins,1 side 0`: BCK low + LRCK high — data for right MSB not yet out; then `set x,16 side 0`, then out bit... So LRCK changes 2 cycles before right MSB — fine (WS setup time relative to latch is what matters; WS must be stable when DAC latches? WS edge must not coincide with latch edge — we're fine: 2 cycles apart? Actually WS transition happens while BCK low — datasheets want WS changing on BCK falling edge ✓). Count per frame: 2+2+32+2+2+32+1 = 71 cycles. Recompute divider: sample_rate = sysclk/(div*71). 150e6/(48000*71)=43.92. div≈43.9453? I'll compute in code: `float div = (float)clock_get_hz(clk_sys) / (SAMPLE_RATE * 71.0f);` — elegant, self-adjusting. Hmm, but sys clock might be 150MHz default on Pico 2. 150e6/48000/71 = 43.918... fine. But wait — check `jmp x-- bitloopL` with x starting 16: outs = 16 (as computed: iteration count until x hits 0: iterations i=1..16, out executes 16 times? Earlier analysis: `set x,16; L: out; jmp x-- L`: jmp results: 16→15...→1→0? jmp #k decrements to 17-k; jumps while ≠0 → k=1..16? k=16: 17-16=1≠0 jump; k=17: 0 no jump → outs=17?? Recount cleanly: x=16. Each loop iteration: `out` then `jmp x--`. Iteration 1: out; jmp: x=15, jump. Iter 2: out; x=14 jump... Iteration i: out; x=16-i; jump iff 16-i≠0 → jump for i=1..15, no jump at i=16 (x=0). So out executes 16 times ✓, jmp executes 16 times ✓ (16 latches) ✓. Sideset timing check for data setup: `out pins,1 side 0` — side 0 → BCK LOW, and out drives DIN in the same cycle. Data changes on BCK low ✓ (spec: data changes on falling edge of BCK — here data changes exactly when BCK goes low, DAC latches on rising BCK (side 1) ✓). Now — one concern: `set pins, 0` and `set pins, 1` need SET pin group configured to LRCK. But also: initial LRCK state before SM starts: set pindirs + `pio_sm_exec(pio, sm, pio_encode_set?...)`? Simpler: run `pio_sm_init` with our program at offset: `start:` executes `set pins,0` first — initial state whatever, converges in a frame. But wait: before SM starts, DMA data in FIFO? Start SM first, then DMA — SM stalls on empty FIFO (autopull), fine. Also: pull threshold 32 with shift-left out: check `out pins, 1` pulls?? No—autopull refills when counter reaches threshold: with shift-left, each out shifts left by 1 and increments counter? Counter counts shifts; when 32 shifts done, OSR "empty" → autopull loads new word at the *next* out (stalls if FIFO empty). Since frames are exactly 32 bits, alignment is automatic. ✓ But CAREFUL: shift direction semantics with `shift_right=false`: `out` takes bits from MSB end and shifts OSR LEFT. Yes, MSB-first. ✓ `sm_config_set_out_shift(&c, false, true, 32)` — first param after c is shift_right=false → shift left → MSB first ✓. Now, will `out pins, 1` output OSR bit 31 before shifting? `out pins, 1`: moves top 1 bit of OSR to pins, then shifts left. ✓ PIO FIFO join TX: `sm_config_set_fifo_join(&c, PIO_SM_FIFO_JOIN_TX)` — RP2350 supports? RP2350 PIO has FIFO join too (and also 8-deep? RP2350 FIFOs: 4 deep, but has "double" join? RP2350 added join modes: TX_PUT? No — RP2350 FIFO join options: none, tx, rx, tx_put, tx_get? RP2350 added `PIO_SM_FIFO_JOIN_TX_PUT`/`TX_GET` — TX_PUT pushes to RX FIFO etc. `PIO_SM_FIFO_JOIN_TX` still exists ✓). Use JOIN_TX for deeper TX FIFO (8 entries? join TX makes 8-deep on RP2350? On RP2040 join TX = 8 deep). Either way safe. Clock divider: `sm_config_set_clkdiv(&c, div)`. PIO program size: 9 instructions ≤ 32 ✓. Now RP2350 SDK API names: all standard `pio_*`, `dma_*` — same as RP2040. `pio_add_program(pio, &i2s_out_program)` and `pio_claim_free_sm?` use `pio_claim_unused_sm(pio, true)`. Generated header via CMake `pico_generate_pio_header`: provides `i2s_out_program`, `i2s_out_program_get_default_config(offset)`. Now the render code specifics. Constants: SAMPLE_RATE 48000? Hmm, allow define 48000 or 44100 (div auto-computed, works either). Actually, why not 48000 default. Buffers: `#define FRAMES_PER_BLOCK 64`, `static uint32_t g_audio[2][FRAMES_PER_BLOCK] __attribute__((aligned(8)))`. Sin table: `static int16_t g_sin_tab[1024] __attribute__((aligned(4)))` init in main: `for i: g_sin_tab[i] = (int16_t)(sinf(2π i/1024)*32767)`. sin lookup inline: ```c static inline int32_t sin_q16(int32_t ph) { // ph in Q16.16 phase (65536 = 1 cycle) return g_sin_tab[(uint32_t)ph >> 6]; // top 10 bits } ``` `(uint32_t)ph >> 6` gives 0..1023 automatically (since 32-bit shift of 26 bits? (uint32_t)ph >> 6: 32-bit>>6 = 26 bits — NOT 10 bits! Need `(ph >> 6) & 1023`. Fix: `g_sin_tab[((uint32_t)ph >> 6) & 1023u]`. But phase as int32 Q16.16 wraps modulo 2^32 naturally ✓ (phase increments small, int32 overflow wraps — and (uint32_t)ph>>6 &1023 = periodic ✓). Wait: Q16.16 phase: one cycle = 65536 → ph spans 0..65535 per cycle; (uint32_t)ph>>6 = 0..1023 when ph in [0,65536)? But ph is a 32-bit number that KEEPS GROWING beyond 65536 (we never mask the accumulator). (uint32_t)ph >> 6 with ph up to 2^32 → gives up to 2^26, need &1023 ✓. So use `g_sin_tab[((uint32_t)ph >> 6) & 1023]` — 4 ops, fine. Alternative: keep phase as uint16_t overflow naturally: phase += inc (uint16 wraps at 65536 = 1 cycle) → then index = phase>>6 (0..1023 automatically!). Use `uint16_t phase; phase += inc;` wrapping = free modulo! Nice: uint16_t phase, increment wraps at 65536 ✓. index = phase>>6 ∈ [0,1023] ✓. FM: modulator phase uint16, carrier phase uint32? carrier phase = accumulate (inc + pm) — pm can be negative → use int32 accumulator with wrap (fine, lookup masks). For carrier use uint32 and add (inc + pm) as int32? Adding negative to uint32 wraps correctly (mod 2^32) ✓. Lookup masks with &1023 after >>6 ✓. Control-rate (every 128 samples): update Lorenz, then params: - `g_rho_q` = pot→ rho_target Q16.16: rho range 1..45? Lorenz chaos ρ≈24.7+. At ρ<~24 periodic, > chaotic — great morph! Pot 0→ρ=8 (periodic calm), pot full → 45 wild. Default mid. - fm carrier inc = f_to_inc(55 + 45*|x|/40 clamp): compute with fixed point: fx = clamp(x, ±40<<16)? |xa| = min(|x|,40<<16)/40<<16 → f = 55 + 45*xa → Q? f in Q16.16? f_c_q = (55+45*xa_frac)<<16? Just compute in integer Hz float-free: ya scaled... Let me define everything Q16.16. Let me write the DSP math concretely (all Q16.16 unless noted): ```c // state int32_t lx, ly, lz; // Lorenz Q16.16 uint16_t ph_c, ph_m, ph_m2; // phases int32_t inc_c, inc_m; // Q16.16 phase increments... wait inc is in phase units per sample: inc = f*65536/SR → small int (e.g., 110Hz → 149). NOT Q16.16 — plain int32. int32_t fm_depth; // Q16.16 (0..~6<<16) int32_t lp_l, lp_r; // one-pole LP state (Q16.16 amplitude ~ samples ±~40000?) ``` Amplitude convention: samples as int32 with ~±24000 nominal (soft clip threshold ~ 26000, hard at 32000). Sine values ±32767; scale drone gain ~12000/32767 → shift: s >> 2 (±8192) then gain via Q16 mul. Lorenz update (every 128 samples): ```c int32_t dx = mulq(10<<16, ly - lx); int32_t dy = mulq(lx, rho - lz) - ly; // rho Q16.16; lz Q16.16 → (rho-lz) Q16.16 ✓; lx*that Q16.16*Q16.16→mulq gives Q16.16 ✓; ly is Q16.16 ✓ int32_t dz = mulq(lx, ly) - mulq(2<<16 + 43691? , lz); ``` β=8/3: 8/3*65536 = 174762 (int) = 0x2AAA A? 8*65536/3 = 174762.67 → 174763? 0x2AAAB. β_q = 174762? fine ≈. ```c lx += mulq(dx, DTQ); // DTQ = 262 (0.004*65536=262.1)... wait mulq(dx, DTQ): dx Q16.16 (units/sec), DTQ Q16.16 seconds → Q16.16 ✓ ``` Hmm but wait: with DT=262 Q16.16 ≈ 0.004 s; velocities: σ(y−x) up to ~10*80=800 → dx ~ 800 Q16.16 = 800<<16; dx*dt = 800*0.004 = 3.2 → lx changes 3.2 per step ~ reasonable. But CAUTION: values x,y,z ∈ up to ~±60 (ρ=45: x ±25? Lorenz x range roughly ± 25? For ρ=45, x ~ ±30, z ~ 0..80). Q16.16 holds ±32767 ✓. Derivative dy uses (rho − lz): rho up to 45<<16, lz up to ~80<<16 → diff −35<<16 ✓. Mapping per control tick: ```c // normalized [-1,1]-ish int32_t xn = clamp(mulq(lx, 2<<16)) etc? ``` Let me define norms: `nx = lx >> 15;` (lx Q16.16 / 32768 → Q16.16 fraction where 32768 units=1.0): lx=40<<16 → 40*65536/32768 = 80 (>>15 gives value*2) hmm let me just: `int32_t nx = clamp_q1(mulq(lx, ONE_OVER_32));` with ONE_OVER_32 = (65536/32)<<16? mulq(lx, K) = lx*K/65536; want lx/32: K = 65536/32 = 2048 → mulq(lx, 2048) = lx/32 in Q16.16 ✓ (lx up to 64<<16 → /32 → 2<<16 → clamp to 1<<16). - f_carrier = 50 + 40*|nx| → inc_c = (f*65536)/48000 = f*65536/48000: f up to 90 → inc ~122. Compute integer: `(50 + (40*|nx|)>>16) * 65536 / 48000`? do: `int32_t f_hz = 50 + ((40 * abs32(nx)) >> 16); inc_c = (f_hz << 16) / SR;` f_hz<<16 / 48000: 90<<16/48000 = 122.88 ✓ (use 64-bit? 90<<16=5.9M fits in int32 ✓). - mod ratio: m = 1 + ny (ny∈[-1,1]) → 0..2 → f_mod = f_carrier*(0.5..2)? f_mod = f_carrier + f_carrier*ny*1? keep: f_mod = f_hz + ((f_hz * ny)>>16) (ratio 0..2, mean 1). inc_m likewise. - fm_depth = pot-based 2..8 <<16? Tie to |ny| drift: depth = (2 + 4*(ρ/45))<<16. - LP coefficient a = cutoff→ alpha = 1 - exp(-2π f_c/SR): precompute table by z: cutoff = 400 + 3600*nz01 (nz01 = clamp(z/90,0,1)): alpha ≈ for 4000Hz@48k: 2π*4000/48000=0.52 → alpha=0.40 (Q16). Approx via alpha = min( (2π fc)/SR, 0.95 ) fine: `a = (628*fc)/48000` (628≈2π*100)? For fc=4000: 628*4000/48000=52→ /100 → 0.52 linear OK (skip exp — one-pole with linear coeff fine sonically). a_q = clamp( (6283*fc)/48000/100? )... let me just: `a = (fc * 414) / 32000;` hmm messy. Choose simple: `int32_t a_q = clamp16( (fc * 2867) / 32000 );` Let me compute properly: alpha ≈ 2π fc/SR = 6.283*fc/48000 = fc*0.0001309. For fc=4000 → 0.5237. Q16: alpha_q = alpha*65536: = fc*85.7 → fc=4000 → 342,900?? no: 0.5237*65536=34,329 ✓ = fc*85.8. So `alpha_q = (fc * 86) >> ? ` fc=4000 → 344,000? That's > 65536! alpha_q must be ≤ 65536 (alpha ≤1): 34,329 < 65,536 ✓ (34,329). fc=8000 → 68,600 → clamp to 60000. OK: `a_q = min(fc*86, 60000)`. - pan: `pan_q = clamp((ny + (1<<16)) >> 1, 0, 1<<16)`. Per-sample drone: ```c ph_m += inc_m (uint16 wrap); int32_t pm = (sin_q16(ph_m) * fm_depth) >> 16; // ±32767*depth(≤8)/65536 → ±depth*... 32767*8>>16 = 4 → pm ±(depth*32767>>16) ≈ ±262k?? ``` wait: sin ±32767 * fm_depth(8<<16=524288) = 17,179,761,... /65536 = 262,144 → pm = ±262,144 phase units (= ±4 cycles) — large FM index! Fine: carrier phase add: `ph_c += inc_c + pm;` pm magnitude 262k → mod spans ±4 cycles — heavy FM (clangorous). Maybe scale depth 0..3 cycles: fm_depth = (pot*3)<<16. pm max = 32767*196608/65536 = 98,303 ≈ ±1.5 cycles. Good. ```c int32_t s_d = sin_q16(ph_c); // ±32767 s_d = (s_d * 9000) >> 15; // gain: 9000/32768 → ±9000? (s_d*9000)>>15: 32767*9000>>15 ≈ 9000 ✓ ``` KS voices per sample: for each active voice: ```c uint16_t p = v->pos; uint32_t L = v->len; int32_t a = v->line[p], b = v->line[p+1==L?0:p+1]; int32_t out = a; // int16 amplitude v->line[p] = (int16_t)((((a + b) >> 1) * v->fb) >> 16); // fb ~ 65000 Q16 if (++v->pos >= L) v->pos = 0; mix += out * v->gain >> 16; ``` Also voice death: track count; when energy low → active=false. Track amplitude: accumulate |out| EMA; kill if tiny after ~len*4 samples? Simple: store `v->age`; decrement per wrap; kill after e.g. 3 seconds? KS decays naturally; kill when `decay_count` expires: count samples since trigger, kill at 2.5s. Excitation on trigger: fill `line[0..len-1]` with `noise = (rand()&0x3FFF)-... ` use xorshift RNG. len = SR/f: f from pentatonic: f = 110 * 2^(st/12): precompute table of 12 pentatonic freqs (A minor pent: semis [0,3,5,7,10,12,15,17,19,22,24]) → compute len = SR/f (100..~873). fb = 65536 - damping: fb = 65400? Higher notes damp faster; set fb = 65000 + pot*? Simple fixed 65280 (0.996). Wait KS line as int16 ±32767 raw noise = loud burst; scale voice gain 8000/32767 → `gain` Q16 = 16000? mix += (out*gain)>>16 with gain=16000 → 16000*32767>>16 = 7999 ✓. Pick note from attractor: `idx = ((ly + 65536) >> 13) % 11`? ly∈[-40,40]<<16: (ly + 40<<16...)... simpler: `uint32_t r = (uint32_t)(lx ^ ly); idx = (r >> 12) & 15; if (idx > 10) idx = 10;` chaos picks. Use xorshift seeded from tick for excitation noise (or LCG): `rng = rng*1664525+1013904223`. Mix: `int32_t mono = s_d + mix;` LP: `lp_l += ((mono - lp_l) * a_q) >> 16;` — int32 ops; values ±20000 fine. Add a touch of the dry: `mono2 = mono - (lp_l >> 2)?` Keep: use lp output mixed with dry: `dr = (mono*3 + lp_l*2)/5`? Use dr = (mono>>1)+(lp_l>>1). HP for DC: dc block: `dc += (dr - dc)>>? ` add: `sig = dr - dc_state; dc_state += (dr-dc_state)*small>>16` — one-pole HP at ~20Hz: coeff 2730 (20Hz/48k: 2π*20/48000=0.0026 → a=0.0026→171 Q16? alpha=2π f/SR=0.00262 → a_q=171). `dc += ((dr - dc)*171)>>16; sig = dr - dc;` Stereo: ```c int32_t l = sig * (PANQ) >> 16 + voice pan stuff; ``` Pan drone by pan_q: `L = mulq(sig, pan_q); R = mulq(sig, (1<<16)-pan_q);` Wait pan 0..1: L=sig*pan? At pan=0.5 equal. Also KS voices: alternate hard L/R with a bit of the other side (0.7/0.3) based on voice index — gives width. Add slight right-channel delay of drone? Keep simple. Add "attractor shimmer": tiny 2nd modulator on right only: `R += ((sin_q16(ph_c2) * 3000) >> 15)` with ph_c2 = carrier phase + offset — decorrelates. Fine: R gets sig2 = one-pole with slightly different a (a2 = a_q*0.8) — implement lp_r with different coeff and feed same mono → mild comb? Simplest width: R uses lp state with different coefficient. OK. Soft clip final: `int16_t L16 = softclip(L), R16 = softclip(R);` ```c static inline int16_t softclip(int32_t x) { if (x > 24000) x = 24000 + ((x-24000)>>2); // hmm overflow if huge; clamp after: ... clamp -32000..32000 } ``` Render block: ```c void render_block(uint32_t *dst) { for (n...) { if ((tick & 127) == 0) control_tick(); // Lorenz + params ... per-sample pipeline dst[n] = ((uint32_t)(uint16_t)L) | ((uint32_t)(uint16_t)R << 16); tick++; } } ``` Boot: init sin table, pre-render blocks, set up PIO/DMA, enable IRQs, launch core1 UI loop, then core0 main loop: maybe print stats occasionally (stdio) — but careful: printf in core0 loop while IRQ renders — fine. UI (core1): ```c absolute_time_t t_btn; bool last_pluck... loop: poll buttons (GP13, GP14 with pull-ups, pressed = low) - on PLUCK press (falling): mailbox_event = 1 - MODE button hold: while held, sweep rho (rho_auto += ) → sets pot override - read ADC0 (pot): adc_read → smooth → g_rho_pot - ghost player: every 4-10s if idle, send ghost pluck event - serial: if char available: 'p' pluck, '+/-' rho, 'd' toggle drone... sleep_ms(10) ``` Mailbox: `volatile uint32_t g_ev;` core1: `g_ev = 1;` core0 control_tick: if g_ev { trigger_pluck(); g_ev = 0; } — also params via `volatile uint32_t g_pot` written by core1, read by core0. Volatile 32-bit aligned = atomic enough on Cortex-M33 ✓. ADC: `adc_init(); adc_gpio_init(26); adc_select_input(0);` read via `adc_read()`. RP2350 ADC API same ✓. Buttons: `gpio_init(13); gpio_set_dir(13, GPIO_IN); gpio_pull_up(14);` etc. stdio: `stdio_init_all()` — with UART default enabled; note GP0/1 UART. But if user uses USB... Pico 2 default: stdio_usb default? In SDK 2.x, `pico_enable_stdio_usb` default 0? and UART default 1 (board config: pico2 board has stdio_uart default enabled? The board header sets `PICO_DEFAULT_UART 0? ` Pico board: UART0 on GP0/1 default stdio UART enabled, USB off). Fine — mention hooking a USB-serial to GP0/1 at 115200. Hmm — note: I should double check `getchar` non-blocking: `int getchar_timeout_us(uint32_t us)` ✓ exists in pico/stdio.h. RNG: xorshift32 static seed; used for excitation + ghost timing. Now — sizes/perf: render per sample: sin×3 lookups + few muls — fine. Potential pitfalls to double-check in code: 1. `sin_q16` index: `g_sin_tab[ph >> 6]` with `uint16_t ph` → int promotion: ph>>6 ∈0..1023 ✓ (65535>>6=1023 ✓). Use `uint16_t` param or cast. 2. Carrier phase: `uint32_t ph_c; ph_c += (uint32_t)(inc_c + pm);` inc_c + pm can be negative → cast wraps ✓. Lookup: `g_sin_tab[(ph_c >> 6) & 1023]` — ph_c>>6 up to 2^26 → mask ✓. Actually simpler: keep carrier phase also in uint16 accumulator! ph wraps at 65536 — with wrap the mod index still valid mod 65536 ✓ since 65536=cycle. pm adds ±X: (uint16_t)(ph_c + inc + pm) — truncation = mod 65536 ✓ correct phase mod one cycle ✓✓. So: `ph_c = ph_c + (uint16_t)(inc_c + pm);` careful: (uint16_t) cast of negative int → wraps mod 65536 ✓. Use `ph_c += (uint16_t)(inc_c + pm);` — but inc_c+pm as int32, cast to uint16 → mod 65536 ✓. BUT modulator freq can be higher than Nyquist? f_mod ≤ 180 Hz fine. Carrier f 50-90 Hz — sub-audio fundamental? FM sidebands make it audible rich (bass drone with FM clang). Fine — plus KS plucks carry melodic content. 3. `mulq` sign: int64 mult of Q16.16 → (int32_t)((int64_t)a*b>>16) ✓ works negative ✓. 4. KS excitation int16: values ±~20000 (noise amplitude): (rand>>?) use `rng = ...; int32_t n = (int32_t)(rng >> 16) - 32768 → ±32767;` too loud vs drone (9000). Voice gain handles (out*gain>>16 with gain 16000 → ±8000 ✓). 5. int16 saturation: use `sat16()`. 6. Potential ISR overrun: block = 64 frames. render 64 samples: say 600 cycles/sample worst → 38k cycles = 253µs < 1333µs ✓ huge margin. 7. DMA size: transfer 32-bit × 64 = FIFO consumption rate 48kHz; DREQ pacing ✓. 8. RP2350 flash cache: place render funcs in RAM: `__not_in_flash_func` or `__time_critical_func` — do for ISR+render. Also add: **Pico 2 specific flavor**: mention `set_sys_clk_khz`? Not needed. Mention RP2350's 150MHz and dual cores used. Wait, I should double check `pio_sm_set_consecutive_pindirs(pio, sm, 16, 3, true)` — signature (pio, sm, uint pins_base, uint pin_count? , bool is_out) — `pio_sm_set_consecutive_pindirs(PIO pio, uint sm, uint pins_base, uint pin_count, bool is_out)` ✓. Also `pio_gpio_init(pio, pin)` per pin ✓ (must call for 16,17,18). Also: SM config `sm_config_set_set_pins(&c, PIN_LRCK, 1)` ✓. PIO start: `pio_sm_init(pio, sm, offset, &c); pio_sm_set_enabled(pio, sm, true);` DMA: DREQ: `pio_get_dreq(pio, sm, true)` ✓. irq: on RP2350 `DMA_IRQ_0` ✓. Also `irq_set_priority(DMA_IRQ_0, ...)`? default fine. Enable order: pre-render both blocks; configure DMA (both channels, IRQs enabled, exclusive handler); start ch0; then enable SM? If SM enabled first it'll pull stale? FIFO empty → stalls on autopull, fine either order. Do: start DMA then SM — DMA DREQ waits for SM FIFO space; SM waits for data → both fine. Start SM last: actually SM pulls from FIFO immediately when data arrives ✓. One more: initial PIO output before program runs: `set pins` needs pindirs — done before enable ✓. Boot sequence in main(): 1. sys clock default (150MHz Pico2? Actually Pico 2 default sys clock = 150 MHz ✓). 2. stdio_init_all. 3. init sin table. 4. gpio/adc init (UI pins on core1? GPIO inits can be in core1's function). 5. setup i2s pio + dma. 6. prerender blocks 0,1. 7. irq handler install. 8. multicore_launch_core1(ui_core1). 9. core0 idle loop with occasional status printf (every 1s: print rho, x,y,z, active voices) — fun serial telemetry. Now, RP2350 double-check for `multicore_launch_core1` — same API ✓. Let me also double check the pioasm syntax details: - `.side_set 1` directive name: `.side_set 1` ✓ (also `.side_set 1 opt` for optional). Non-optional: every instruction needs side value or defaults 0 ✓. - `set pins, 0 side 0` — SET source "pins" ✓. - `jmp x-- label side 1` ✓. - `out pins, 1 side 0` ✓. - Labels ✓. - max 16-bit instructions ✓ (uses 8 bits delay/sideset + operand fields — SET x,16: operand 16 fits 5 bits ✓ (0-31)). Cycle count re-verify (71 cycles/frame): set pins(1) + set x(1) + [out+jmp]×16 (32) + set pins(1) + set x(1) + [out+jmp]×16 (32) + jmp start(1) = 1+1+32+1+1+32+1 = 70. Hmm: 2+32+2+32+1 = 69? 1+1=2; +32=34; +1+1=36; +32=68; +1=69. 69 cycles/frame. Fine — divider formula: use FRAME_CYCLES 69: div = sysclk/(SR*69). I'll count carefully in code comment: define CYCLES_PER_FRAME 69. Let me recount: instructions executed per frame: start: `set pins,0`(c1), `set x,16`(c2), then loop L: 16×(`out`(c), `jmp x--`(c)) = 32 (c3..c34), `set pins,1`(c35), `set x,16`(c36), loop R 32 (c37..c68), `jmp start`(c69). → 69 ✓. div = 150e6/(48000*69) = 45.289... `pio_sm_set_clkdiv(pio, sm, div)` accepts float — `sm_config_set_clkdiv(&c, divf)`. Use float division; RP2350 divider supports fractional (8.8) ✓. Jitter from fractional divider — fine for audio. Sample rate exactness: 150e6/69/45.289855 = 48000 ✓ approx; tiny error fine. Now the KS voice struct & polyphony: 4 voices round-robin. `voice_trigger(int idx)` picks next voice slot, fills, sets len/pos/fb/age. Note freq table: A2=110Hz minor pentatonic 2.5 octaves: semitones [0,3,5,7,10,12,15,17,19,22,24] → 11 notes: f = 110*2^(s/12). Precompute inc directly? KS needs len = SR/f: SR=48000: 110→436, 110*2^2=440→109. len range 109..436 < 1024 ✓. But wait — if SAMPLE_RATE changes to 44100: len max = 44100/110=401 ✓ <1024. Use `#define KS_MAX 512` and table computed at init from SR. Excitation fill: for i> 16) - 32768;` then smoothing: `v = (r>>2) + (lastv>>2)?`... Simple: `exc = r - (last>>2); last = r;` hmm keep: lowpass: `cur = cur + ((r - cur)*3>>2);` gives mellow pick. Or "burst" for brightness. Fine: one-pole a=0.5: `cur = (cur + r)>>1; line[i]=cur>>?`. Ghost autoplay: core1 every 3-8s (rng): g_ev=1 with flag ghost (maybe mailbox encodes note choice? keep same). Mailbox: `volatile uint32_t g_ev_pluck; volatile uint32_t g_pot_raw;` Also `g_mode` if needed. Core1 also handles: MODE button held → pot-auto-sweep: g_pot override cycles: implement as core1 computing `g_rho_target` directly: core1 reads pot & buttons → writes `g_rho_target` (Q16.16, smoothed there). Core0 control_tick lerps actual rho toward target (avoid clicks: rho changes slowly — Lorenz parameter changes integrate fine). Core1 code: ```c static uint32_t rng; void core1_main() { gpio buttons init; adc init; uint32_t smooth_pot=0; last_press_t; while (1) { // pot adc_select_input(0); uint32_t p = adc_read(); smooth_pot = (smooth_pot*255 + p)>>8; uint32_t rho_t = 8<<16 + ((smooth_pot * (37<<16)) >> 12) / ... ``` map pot 0..4095 → rho 8..45: `rho_t = (8<<16) + ((smooth_pot * 37) << 16)/4096` = 8 + pot*37/4096 in Q16: `(8<<16) + ((uint64_t)smooth_pot * 37 * 65536 / 4096)`: simplify `rho_q = (8<<16) + (smooth_pot * (37<<16) / 4096)` careful overflow: smooth_pot≤4095, 37<<16=2.4M → product 1e10 needs 64-bit: use ((uint64_t)). Or scale: `rho_q = (8<<16) + ((smooth_pot * 2425) >>? )` 37*65536/4096 = 592.66: `rho_q = (8<<16) + smooth_pot*592;` smooth 4095*592 = 2.42M + 0.52M ✓ fits. MODE hold: while held, add auto sweep: `rho_q = 8 + ((tick>>?)...)` implement: if mode_held: rho_target = 8 + ((millis()>>9)&0x3F)?? make saw 8..45: `(t/64 ms % 37) + 8`. Fine. - PLUCK press → g_ev_pluck = 1 (edge detect with debounce 20ms). - ghost: every (rng 3000-8000 ms) → g_ev_pluck=1. - serial: `int c = getchar_timeout_us(0); if (c>0) { if 'p' g_ev_pluck=1; ... }` - write `g_rho_target = rho_q`. - sleep_ms(5); ``` Core0 control_tick (every 128 samples = 375Hz): - lerp rho: `g_rho += (g_rho_target - g_rho)>>10;` - Lorenz step (2 substeps for stability? 1 fine). - events: `if (g_ev_pluck) { g_ev_pluck=0; ks_trigger_from_attractor(); }` - params: recompute inc_c, inc_m, a_q, pan_q, fm_depth. Wait — event latency: control tick every 128 samples (2.7ms) — imperceptible ✓. Everything core0: ISR render — needs the event check inside block loop (control_tick). ✓. Also initial attractor state: x=-8, y=8? classic: (0.1, 0, 0)? Use (8, 12, 20) Q16.16 → interesting. Alright — also think: does drone sound good? FM bass drone with modulator ratio ~1 (inharmonic clang), depth pot→ clangy. Add detuned second carrier? Add fifth? Keep, plus note that knobs/patches are tweakable. Actually, let me add one more creative element to strengthen "novel creative": **the pluck excitation noise is seeded from the Lorenz state** (chaos literally "plucks" — the burst noise pattern derives from attractor coordinates) — poetic. And maybe: **after each pluck, briefly "kick" the attractor** (add impulse to x based on note) — the melody feeds back into the drone timbre — a feedback loop between composition and timbre. That's a genuinely novel twist: **composer↔timbre coupling**. Love it. Include comment. Now write the final code. Also CMakeLists: ```cmake cmake_minimum_required(VERSION 3.13) include(pico_sdk_init.cmake) # via $PICO_SDK_PATH project(chaosynth C CXX ASM) set(CMAKE_C_STANDARD 11) pico_sdk_init() add_executable(chaosynth chaosynth.c) pico_generate_pio_header(chaosynth ${CMAKE_CURRENT_LIST_DIR}/i2s_out.pio) target_link_libraries(chaosynth pico_stdlib hardware_pio hardware_dma hardware_adc pico_multicore) pico_add_extra_outputs(chaosynth) # uf2 pico_enable_stdio_usb_default(chaosynth 0)? default anyway ``` Standard: `pico_sdk_init()`, add pico_multicore, hardware_*. `pico_add_extra_outputs(chaosynth)`. Now write chaosynth.c fully. Let me draft mentally and double check each API call: ```c #include "pico/stdlib.h" #include "pico/multicore.h" #include "hardware/pio.h" #include "hardware/dma.h" #include "hardware/adc.h" #include "hardware/irq.h" #include "hardware/clocks.h" #include #include "i2s_out.pio.h" ``` `clock_get_hz(clk_sys)` from hardware/clocks.h ✓. Globals: ```c #define SAMPLE_RATE 48000 #define FRAMES_PER_BLOCK 64 #define CYCLES_PER_FRAME 69 static uint32_t g_audio[2][FRAMES_PER_BLOCK]; static int16_t g_sin[1024]; ``` Sin init: ```c for (int i=0;i<1024;i++) g_sin[i] = (int16_t)lrintf(sinf(2.f*M_PI*i/1024.f)*32766.f); ``` include math.h; on pico, sinf from libm — pico-sdk links libm ✓ (use `__aeabi`? just sinf fine). sin lookup: ```c static inline int32_t sin_q(uint32_t ph16){ // ph16: phase mod 65536 in low 16 bits of uint32 return g_sin[(uint16_t)ph16 >> 6]; // wait need ph>>6 & 1023: (uint16_t)ph16>>6 gives 0..1023 ✓ } ``` Take `uint16_t phase` argument: `sin_q(uint16_t ph)` → `g_sin[ph>>6]` ✓ (0..1023 ✓). Lorenz globals Q16.16: ```c static int32_t g_x = 8<<16, g_y = 12<<16, g_z = 20<<16; static int32_t g_rho = 24<<16, g_rho_target = 24<<16; ``` mulq: ```c static inline int32_t mulq(int32_t a, int32_t b){ return (int32_t)(((int64_t)a*b)>>16); } ``` Check: a,b Q16.16 → product Q32.32 >>16 → Q16.16 ✓. Range: values ≤ 2^31/32768? g_x ≤ 80<<16 = 5.2M; times DTQ 262: 1.4e9 <2^31/... (int64) fine ✓. Lorenz step: ```c #define SIGMA (10<<16) #define BETA 174762 // 8/3 Q16.16 #define DTQ 246? // 0.00375? use 262 static void lorenz_step(void){ int32_t dx = mulq(SIGMA, g_y - g_x); int32_t dy = mulq(g_x, g_rho - g_z) - g_y; int32_t dz = mulq(g_x, g_y) - mulq(BETA, g_z); g_x += mulq(dx, DTQ); g_y += mulq(dy, DTQ); g_z += mulq(dz, DTQ); } ``` Overflow check: g_x up to ~±32 (ρ=45): g_x=±32<<16 = 2.1M; (g_rho − g_z): 45<<16 − up to 90<<16 = −2.9M... wait z for ρ=45 goes up to ~ 2ρ≈ 90?? Lorenz z range ~ [0, ~ρ+something]; with ρ=45 z ≤ ~90 → 5.9M; diff −5.5M. mulq(g_x, diff) = 2.1M*5.5M=1.2e13 → int64 ✓ >>16 = 1.8e8 < 2^31 ✓ (fits int32 ✓). dy = 1.8e8 − 0.8M ≈ ok. mulq(dy≈1.8e8, DTQ=262): 4.7e10 int64 ✓ >>16 = 7.2e5 → g_y += 7.2e5 = 11 Q16.16 units — hmm g_y=12 means value 12<<16=786k; delta 7.2e5?? That's dy*dt: 1.8e8 Q16.16 * 0.004 = 7.2e5 = 0.004*1.8e8=7.2e5 → in Q16.16 units that's 7.2e5/65536 = 11 → y changes 11 units/step — large but Lorenz derivative magnitude ~ x(ρ−z) ≈ 30*... yes dy ~ 30*45−12 ~ 1300/step sim? With dt 0.004: actual dy/dt = 30*(45−90)=−1350 → *0.004 = −5.4. Consistent. Euler with dt=0.004 on Lorenz: stable? Lorenz max eigen ~ σ+1+... The fast z mode: dz/dt = xy−βz: slope −β=−2.67; x*y up to 30*35=1050?? dz/dt=1050 → dt*dz = 4.2/step, fine. Stability: |1−β dt|=0.99 ✓; x-mode: −σ..(ρ−1): up to 44*0.004=0.176 ✓. Euler OK-ish; Lorenz with Euler dt=0.004 slightly energy-biased but that's FINE for art (chaotic anyway). Maybe use dt=0.003 → DTQ=197 for margin. Eh: 262 (dt=0.004) acceptable. Actually careful: known Lorenz Euler stability requires dt < ~2/(σ+ρ+...)≈0.01+ — 0.004 ✓. Audio params (recomputed in control tick): ```c static uint16_t ph_c, ph_m; static int32_t inc_c, inc_m, fm_depth; // inc: phase units/sample; depth: phase units (scaled by sine amplitude) ``` Wait fm depth: pm = sin_q(ph_m) * fm_depth >> 16 — fm_depth in Q16.16 phase-units? pm target ±1.5 cycles = ±98304 phase units: sin ±32767 * fm_depth >>16 = fm_depth/2 → want ±98304 → fm_depth = 196608. OK define fm_depth in "phase units << 16". control_tick: ```c static int32_t a_lp, pan_l, pan_r, lp_state; ... ``` Full control_tick(): ```c static void control_tick(void){ g_rho += (g_rho_target - g_rho) >> 12; lorenz_step(); // normalized int32_t nx = g_x >> 15; // ~ /32768 → ±32*2=±64?? g_x=32<<16 → >>15 = 64 → 64<<16? ``` Hmm: g_x Q16.16: value v stored as v*65536. `>>15` → v*2 → Q16.16 of (v/16*32)?? I'm overcomplicating: nx = mulq(g_x, 4096) → g_x/16 → |nx| ≤ 2<<16 (v≤32). Want nx = clamp(g_x/32): mulq(g_x, 2048): v=32 → 32<<16*2048>>16 = 32*2048=65536*? no: mulq(a,2048)=a*2048/65536 = a/32 → g_x=v*65536 → nx = v*2048 → v=32 → nx=65536=1.0<<16 ✓. So nx=mulq(g_x,2048), clamp ±1<<16 → represent as Q16.16 fraction. ```c int32_t nx = sat1q(mulq(g_x, 2048)); int32_t ny = sat1q(mulq(g_y, 2048)); int32_t nz = g_z < 0 ? 0 : (g_z > (90<<16) ? (1<<16) : mulq(g_z, 728)); // z/90 → 65536/90=728 ``` Then: ```c int32_t ax = nx < 0 ? -nx : nx; int32_t f_hz = 48 + (ax >> 12) * 60; // hmm ``` Let me be careful: f_carrier Hz = 48 + 60*|nx_norm| where nx_norm∈[0,1]: |nx| is Q16.16: f = 48 + ((ax * 60) >> 16). ✓ (ax ≤65536 → ≤60). ```c int32_t f0 = 48 + ((ax * 60) >> 16); // 48..108 Hz carrier inc_c = ((int32_t)f0 << 16) / SAMPLE_RATE; // wait: inc = f*65536/SR: f0<<16 = up to 7.1M ✓ /48000 → 147 ✓ ``` Hmm (f0<<16)/48000: 108<<16=7.08e6/48000=147 ✓. ```c int32_t f_m = f0 + mulq(f0<<16? ... ``` mod freq: ratio r = 1 + ny/1 → f_m = f0 + f0*ny_norm: ```c int32_t fm_hz = f0 + ((f0 * ny) >> 16); // f0 * ny(Q16) → /65536 ✓ inc_m = ((int32_t)fm_hz << 16) / SAMPLE_RATE; ``` fm_hz up to 216 (ny=1) → inc 295 ✓ (below Nyquist? 216Hz « 24k ✓). ```c fm_depth = (int32_t)(g_rho >> 3) + (1<<17)?? ``` depth from rho: rho 8..45 Q16 (0.5M..3M): depth cycles 0.5..3: fm_depth = (g_rho * 3)>>? g_rho Q16: rho_norm=rho/45: depth = 196608*(0.4 + 0.6*rho/45)? Keep: `fm_depth = 65536 + (g_rho >> 2);` rho=45<<16=2.95M >>2 = 737k → depth=0.8M → pm = 32767*0.8M>>16 = 400k phase units = 6 cycles — too much? At chaos it'll be wild clang — maybe cap: depth = min(..., 400000). Let me set: `fm_depth = 131072 + (g_rho >> 3)` → at rho45: 131k+368k=500k → pm ±32767*500k/65536 = ±250k = ±3.8 cycles. Heavy but that's "chaos mode" — the drone gets gnarly; at rho8: 131k+65k=196k → ±1.2 cycles mild. Good gradient ✓. ```c // LP cutoff from z int32_t fc = 300 + ((nz * 3800) >> 16); a_lp = (fc * 86) >> ? ``` alpha_q = fc*86 (α*65536 ≈ fc*85.9): fc=4000 → 344000 — wait that exceeds 65536! α = 2π fc/SR = 6.28*4000/48000 = 0.523 → α*65536 = 34,290 ✓ = fc*85.7? 4000*85.7=342,800. NO: fc*85.7 = 342,800?? 4000*85.7 = 342,800. But α*65536 = 0.523*65536 = 34,290. So factor = 34,290/4,000 = 8.57! Not 85.7. α = 6.28*fc/48000 = fc*0.000131 → *65536 = fc*8.58. YES: a_q = fc*8 (or *8.58 → use (fc*437)/51? just fc*9 with clamp): fc up to 4100 → a=36,900 <65536 ✓. Good: `a_lp = fc * 9;` (slightly hot, clamp to 60000). Hmm wait check fc: 300 + 3800*1 = 4100 → a = 36,900 ✓. ```c // pan from y: ny ∈ [-1,1] → pan 0.1..0.9 pan_l = (3<<14) + ((ny + (1<<16)) >> 2); // messy ``` Simplify: pan = (ny + 3<<15)/2... let me: pan ∈ [0.15, 0.85]: pan = 9830 + ((ny + (1<<16)) * 22938 >> 16)?? Simpler integer: `int32_t pan = ((ny + (1<<16)) >> 1) - (14<<12);` ugh. Do: `pan_q = sat(mulq(9830 + ... ))`... Easiest: ```c int32_t p = (ny >> 1) + (1<<15); // 0..32768 → 0..0.5 p = 9830 + p; // 0.15..0.65 Q16? values: 9830..~42600 (units of Q16 fraction*65536?) ``` Hmm units: treat p as Q16.16 fraction: ny Q16.16 (±65536): ny>>1 = ±32768; +32768 → 0..65536 ✓ = fraction 0..1 Q16.16 ✓. p = 9830 + 0.7*(that): `p = 9830 + mulq(p0, 45875)`: p0∈[0,65536] *0.7 → 45875 Q16.16? mulq(p0, 45875) = p0*45875/65536 = p0*0.7006 ✓. p ∈ [9830(0.15) .. 0.15+0.7=55731(0.85)] ✓. pan_l=p, pan_r=(1<<16)−p. KS trigger: ```c static void ks_trigger(void){ voice_t *v = &g_voice[g_next_voice++ & 3]; // attractor picks the note (pentatonic minor on A) uint32_t r = (uint32_t)(g_x ^ g_y ^ (g_z*3)) ; r ^= r >> 13; uint32_t idx = (r >> 10) % 11; int32_t f = g_pent[idx]; // Hz Q16.16? store as Q16.16 Hz? len needs SR/f: f Q16: len = ((SR<<16)/f)>>16 = (SR*65536)/f: uint32_t len = (uint32_t)(((((uint64_t)SAMPLE_RATE) << 32) / (uint64_t)f) >> 16); // Q16: (SR<<32)/fHzQ16 → SR/f *65536; >>16 → SR/f ✓ if (len < 8) len = 8; if (len > KS_LINE-2) len = KS_LINE-2; v->len = len; // excite: noise burst shaped by attractor state (chaos plucks the string) uint32_t s = r; int32_t lp = 0; for (int i=0;i<(int)len;i++){ s ^= s<<13; s ^= s>>17; s ^= s<<5; // xorshift32 int32_t n = (int32_t)(s >> 16) - 32768; // ±32767 lp = (lp + n) >> 1; v->line[i] = (int16_t)(lp>>1); } v->pos = 0; v->age = SAMPLE_RATE*2; v->active = true; // couple melody back into the attractor (the composition perturbs its composer) g_x += (int32_t)(idx - 5) * (4000); g_z += 8000; } ``` Check xorshift32: standard: x^=x<<13; x^=x>>17; x^=x<<5 ✓ (needs nonzero seed ✓ from r). Pentatonic: computed at init: `g_pent[i] = 110<<16 * 2^(st/12)`: use float at init: ```c static int32_t g_pent[11]; const int semis[11] = {0,3,5,7,10,12,15,17,19,22,24}; init: g_pent[i] = (int32_t)(110.0f * powf(2.f, semis[i]/12.f) * 65536.f); ``` powf needs -lm? pico sdk links libm automatically? `pico_stdlib`? For safety use `expf(0.6931*s/12)`: same lib. The SDK does link libm (mbed? pico platform links m) ✓ I'm fairly confident pico SDK links libm by default. Alternatively precompute with repeated multiplication: 2^(s/12) = product... simpler: hardcode float constants: `const float pentf[11] = {110,130.81,146.83,164.81,196,220,261.63,293.66,329.63,392,440};` — hardcode ✓ no libm needed except sinf for table. sinf also libm... For the sin table, could compute without libm? Use `sin` via libm — pico SDK DOES link libm by default (pico_standard_link includes m). Yes: `target_link_libraries` pico_stdlib → hardware... pico platform links libm — I'm confident (common to use sinf in pico examples? e.g., FFT examples use sin). OK fine — but simplest robust: build table with a small fixed-point recurrence? Just use sinf; it's standard. Voices render (in per-sample loop): ```c static int32_t mix_v = 0; for (int k=0;k<4;k++){ voice_t *v = &g_voice[k]; if (!v->active) continue; uint32_t L = v->len, p = v->pos; int32_t a = v->line[p]; int32_t b = v->line[p+1 == L ? 0 : p+1]; int32_t lp2 = (a + b) >> 1; v->line[p] = (int16_t)mulq(lp2, 65536 - (DAMP)); ... ``` fb: 0.996 → 65274. Store per voice (could vary by pot for dampening): v->fb = 65274 fixed. ```c v->pos = p+1 >= L ? 0 : p+1; int32_t s = a; // tap // pan voices alternately L/R int32_t g = (k & 1) ? 10000 : 9000; if (k & 1) mix_r += mulq(s, 14000); mix_l += mulq(s, 6000); ... ``` Wait need separate L/R voice mix: `vmix_l += (s*12000)>>16; vmix_r += (s*7000)>>16` for even, swapped odd. Actually simpler: alternate pan: even voice → pan L (0.7/0.3): vmix_l += mulq(s, 16000*pan...) — just: if k even: vl += s*7>>? Let me use: `vl += mulq(s, 1200? )`... Keep clean: amplitude scale 10000/32767 ≈ 0.3 → mulq(s, 20000) → 32767*20000>>16 = 10000. For L: 20000, R: 12000 (even voice), reversed odd. OK. Also handle excitation output loudness: excitation fill ±16384 (lp>>1 of ±32767 → ±8k? noise n ±32767, lp=avg → ±16k, >>1 → ±8k) then loop damps — string energy at 8k*0.3 = 2.4k — quiet-ish vs drone 9000. Bump voice gain: use 32000/20000: 8k*32000>>16 = 4000 ✓ decent. Let me not over-tune; values chosen sensibly. Age: `if (v->age) v->age--; else v->active = false;` Per-sample render: ```c static void __time_critical_func(render_block)(int buf_idx){ uint32_t *dst = g_audio[buf_idx]; for (uint i=0;i>16 = ±6000 // wait mulq(sin, 12000) = sin*12000/65536 → ±6000 ✓ // KS voices int32_t vl=0, vr=0; ... loop ... int32_t mono = drone + ((vl+vr)>>1); // one-pole LP (brightness follows z) lp_l += mulq(mono - lp_l, a_lp); lp_r += mulq(mono - lp_r, a_lp*?...); // vary for width: use (a_lp>>1)? then lp_r differs → width. Actually different cutoff R vs L → spectral width ✓ int32_t dl = mono + mulq(lp_l, 12000)?? ``` Hmm — mixing dry+LP: `dry = mono` (±?) drone 6000 + voices 4000 → ±10000; lp_l similar scale. Output: `sig_l = (mono>>1) + (lp_l>>1)` ≈ mono... pointless. Better: sig = lp_l (filtered) + some pre-emphasis? Just: `sig_l = lp_l + ((mono - lp_l) >> 2);` (mostly filtered, slight dry). And right: `sig_r = lp_r + ((mono - lp_r) >> 2);` with lp_r cutoff different → width ✓. Then drone pan + voice pan already separate? I put voices into vl,vr pre-pan; drone into mono then pan? Then pan of drone via pan_l/pan_r: ```c int32_t l = mulq(sig_l, pan_l) + vl; int32_t r = mulq(sig_r, pan_r) + vr; ``` Hmm pan_l+pan_r = 1 → constant power-ish ✓. DC blocker: ```dc_l += ((l - dc_l) * 273) >> 16; ... 273 Q16? coeff 0.00416? a=171 (20Hz): (l−dc)*171>>16 ✓ l -= dc_l; ``` Wait dc state scale: values ±12000 ✓. Soft clip + pack: ```c int32_t L16 = softclip16(l), R16 = softclip16(r); dst[i] = ((uint32_t)(uint16_t)L16 << 16) | ((uint32_t)(uint16_t)R16 & 0xFFFFu); ``` Note: LEFT in HIGH 16 bits (MSB first) ✓. softclip: ```c static inline int32_t softclip(int32_t x){ if (x > 20000) { x = 20000 + ((x-20000)>>2); } else if (x < -20000) { x = -20000 - ((-x-20000)>>2); } if (x > 32000) x = 32000; if (x < -32000) x = -32000; return x; } ``` ISR: ```c static void __isr? dma_handler(){ uint32_t ints = dma_hw->ints0;? or use sdk if (dma_channel_get_irq0_status(g_dma_ch[0])) { dma_channel_acknowledge_irq0(g_dma_ch[0]); render_block(0); } ... } ``` `__not_in_flash_func` on handler. Since handler calls render_block (in RAM too). Hmm: `dma_channel_get_irq0_status` — double-check existence in SDK 2.1: yes, `dma_channel_get_irq0_status(uint channel)` (added 1.5). OK. Also handler name registration: `irq_set_exclusive_handler(DMA_IRQ_0, dma_handler); irq_set_enabled(DMA_IRQ_0, true); dma_channel_set_irq0_enabled(ch0,true); dma_channel_set_irq0_enabled(ch1,true);` PIO setup: ```c static void i2s_init(void){ pio = pio0; sm = pio_claim_unused_sm(pio, true); offset = pio_add_program(pio, &i2s_out_program); for pin 16..18: pio_gpio_init(pio, pin); pio_sm_set_consecutive_pindirs(pio, sm, PIN_DIN, 3, true); pio_sm_config c = i2s_out_program_get_default_config(offset); sm_config_set_out_shift(&c, false, true, 32); // MSB first, autopull 32 sm_config_set_out_pins(&c, PIN_DIN, 1); sm_config_set_sideset(&c, 1, false, false); // wait — get_default_config already sets sideset count from program metadata! ``` Hmm: `program_get_default_config` automatically sets sideset pins?? It sets sideset COUNT from the program but base comes from `sm_config_set_sideset_pins`. Actually pioasm-generated `__asm_output`? The default config sets: `sm_config_set_sideset(&c, pio->...`? The generated `_get_default_config` sets out/in/set/sideset counts based on program's pin groups (the `.pio` metadata: sideset count from `.side_set 1`; out pins count 1 from `out pins` usage? Not exactly — pioasm records sideset count in `pio_program.sideset_base?` The generated header has fields: `.sideset_base? no. In `_get_default_config`: it does `sm_config_set_wrap...`, `sm_config_set_sideset(&c, program->sideset? ...)`. I recall the default config does NOT set sideset count automatically — examples call `sm_config_set_sideset(&c, 1, false, false)` explicitly? Hmm: pico-examples ws2812: uses `ws2812_program_get_default_config(offset)` then `sm_config_set_set_pin_base? ` ws2812 has `.side_set 1` and example does NOT call sm_config_set_sideset — because generated default config handles sideset count+optionality from the program. Yes: `pio_sm_config c = program_get_default_config(off)` → `sm_config_set_sideset(&c, program->sideset_base... ` hmm, I believe pioasm generates `.sideset` info and default config sets sideset count. To be safe: calling `sm_config_set_sideset(&c, 1, false, false)` again is harmless (idempotent). I'll include it explicitly. And `sm_config_set_sideset_pins(&c, PIN_BCK)` needed (base pin always needed). - `sm_config_set_set_pins(&c, PIN_LRCK, 1)` ✓. - `sm_config_set_fifo_join(&c, PIO_SM_FIFO_JOIN_TX)` ✓. - `sm_config_set_clkdiv(&c, (float)clock_get_hz(clk_sys) / (SAMPLE_RATE * CYCLES_PER_FRAME))` ✓. - `pio_sm_init(pio, sm, offset, &c); pio_sm_set_enabled(pio, sm, true);` DMA init: ```c int ch0 = dma_claim_unused_channel(true), ch1 = dma_claim_unused_channel(true); for two channels: config: size 32, read inc true, write inc false, dreq pio tx, chain to other, sniff off default. dma_channel_configure(ch0, &cc0, &pio->txf[sm], g_audio[0], FRAMES_PER_BLOCK, false); dma_channel_configure(ch1, &cc1, &pio->txf[sm], g_audio[1], FRAMES_PER_BLOCK, false); ``` Then pre-render block0/1, enable IRQ, `dma_channel_start(ch0)`... hmm — wait: `dma_channel_start` triggers ch0; but ch1 will be triggered by ch0's completion chain ✓. But ALSO: ch1 is not "armed"?? chain trigger starts it regardless ✓. And ch0 restart via ch1 chain ✓. Good. Actually careful: `dma_channel_start(ch0)` — for RP2350 same API ✓. One subtlety: write address `&pio->txf[sm]` — RP2350: `pio->txf[sm]` ✓ (txf is array of volatile uint32_t). Now UI core1: ```c void core1_entry(void){ // buttons const uint BTN_PLUCK = 14, BTN_MODE = 13; gpio_init(BTN_PLUCK); gpio_set_dir(BTN_PLUCK, GPIO_IN); gpio_pull_up(BTN_PLUCK); same MODE; adc_init(); adc_gpio_init(26); adc_select_input(0); uint32_t pot = 0; bool last_pluck = true, mode_held=false; uint32_t t_ghost = 5000, rng = 0x2A5F1E3D; absolute_time_t next = make_timeout_time_ms(5); while (true) { // pot → rho target 8..45 uint32_t raw = adc_read(); pot = (pot * 255 + raw) >> 8; uint32_t rho_q = (8 << 16) + pot * 592; // 0..4095*592 = 2.43M → up to 8+... 2.43M/65536=37 → 45 ✓ bool mode = !gpio_get(BTN_MODE); bool plk = !gpio_get(BTN_PLUCK); if (mode) { // hold to auto-sweep rho uint32_t t = to_ms_since_boot(get_absolute_time()); rho_q = (uint32_t)(8 + ((t >> 8) % 37)) << 16; } g_rho_target = (int32_t)rho_q; if (plk && !last_pluck) g_ev_pluck = 1; last_pluck = plk; // ghost pluck if (to_ms_since_boot(get_absolute_time()) > t_ghost) { g_ev_pluck = 1; rng ^= rng << 13; rng ^= rng >> 17; rng ^= rng << 5; t_ghost = to_ms_since_boot(get_absolute_time()) + 2500 + (rng & 0xFFF); // +0.25..~4.4s } // serial commands int c = getchar_timeout_us(0); if (c == 'p' || c == ' ') g_ev_pluck = 1; else if (c == 'c') g_ghost = !g_ghost;? keep simple: p and q(?) — fine: 'p' pluck, 'r' reseed attractor: g_reseed flag → core0 sets random-ish state. sleep_until(next); next = delayed_by_ms(next, 5); } } ``` Note adc_read: also need `adc_select_input(0)` once ✓. `to_ms_since_boot` returns uint64 ✓ — comparison types: use `uint32_t t = (uint32_t)to_ms_since_boot(...)`. 'p','r' handling: g_ev_pluck, g_ev_reseed as volatile uint32_t. Core0 main: ```c int main(){ set_sys_clock? default. stdio_init_all(); // sin table for (int i = 0; i < 1024; i++) g_sin[i] = (int16_t)lrintf(sinf(2.0f * M_PI * i / 1024.0f) * 32766.0f); for (int i=0;i<11;i++) g_pent[i] = (int32_t)(110.0f * powf(2.0f, g_semis[i] / 12.0f) * 65536.0f); i2s_init(); // pio setup dma_init(); render_block(0); render_block(1); irq_set_exclusive_handler(DMA_IRQ_0, dma_isr); dma_channel_set_irq0_enabled(ch0, true); dma_channel_set_irq0_enabled(ch1, true); irq_set_enabled(DMA_IRQ_0, true); multicore_launch_core1(core1_entry); dma_channel_start(ch0); pio_sm_set_enabled(pio, sm, true); // hmm order: enable SM before DMA start? // status prints every 2s on core0 while (true) { sleep_ms(2000); printf("[chaosynth] rho=%.1f x=%+6.2f y=%+6.2f z=%+6.2f pot=%u\r\n", g_rho/65536.f, g_x/65536.f, g_y/65536.f, g_z/65536.f, ...); } } ``` Careful: printf with %f — pico printf supports %f if `PICO_PRINTF`? default newlib nano? pico_enable_printf... Default SDK printf (custom pico_printf?) supports float? By default, pico uses standard newlib with full printf? Pico SDK default: `pico_use_printf`... The SDK's default printf is the standard one supporting floats IF not the 'pico' minimal. To dodge risk: print fixed-point manually: print g_rho>>16 as int etc. Use integers: `printf("rho=%d x=%d y=%d z=%d (int units)\r\n", (int)(g_rho>>16), ...)`. Safer ✓. `main` also should init UI?? core1 does its own gpio/adc init ✓. Order matters: enable SM before DMA? If DMA starts first, writes FIFO (depth 8 with join) until full, SM not consuming — no harm; when SM enables it drains. Data alignment: FIFO order preserved ✓. Enable SM first, then start DMA — cleaner. Also IRQ before start ✓. Potential issue: `irq_set_exclusive_handler(DMA_IRQ_0...)` — and both channel IRQs on IRQ0. During handler both flags might be set (if both complete... impossible: they're chained serially; ch1 only runs after ch0 completes; handler for ch0 runs within 1.3ms; ch1 completes 1.3ms later — handler re-enters. But what if handler for ch0 is delayed beyond ch1 completion? Then ints would show both — handler handles both flags sequentially ✓ (my handler checks both). Edge: at start, ch0 runs immediately (DMA start) → completes 64 frames later → chains ch1 (which starts reading buf1) + IRQ → we render buf0. ✓ Now, RP2350 concerns: - `pio->txf` ✓ same. - DMA `dma_hw` ✓. - Cortex-M33: ISR latency fine. - `__time_critical_func` places in .time_critical (RAM) ✓; also `__not_in_flash_func`. Use `__not_in_flash_func` for ISR & render (SDK defines both macros ✓). - XIP cache: flash execution OK anyway. - Multicore: core1 launched after IRQs running — g_ volatile variables shared ✓. Boot button? Not using BOOTSEL — GPIO buttons instead. Fine, and I'll note GP14 default: if no button attached, internal pull-up makes it read 1 (not pressed) ✓ safe. Pot floating: adc floats around → rho jitters — add: if raw reads <100 or >4000?? floating pin gives erratic mid values... Note in wiring docs: tie pot; else auto-sweep mode default? Simplest: note in README comments. Also add: if pot unplugged (raw bounces wildly), ghost still plays. Acceptable. Now also double check `sm_config_set_out_shift(&c, false, true, 32)`: shift_right=false → shift LEFT → MSB first ✓; autopull=true, threshold=32 → refills after 32 bits ✓. Wait, actually, I want to double-check the semantics: with autopull, does the pull happen at the END of 32nd shift, meaning the next `out` sees fresh data ✓. There's a subtlety: autopull with threshold 32 reloads when shift counter hits 32 — the counter is set to 32-pull_threshold? Standard config: pull_threshold=32 → OSR refills when fully empty ✓. Also: must NOT have `sm_config_set_in_shift` needed (no input) ✓. PIO wrap: program doesn't use wrap — uses explicit jmp start ✓. Default wrap settings from generated header are harmless (wrap target=program start? default wrap is program start to end — but we jmp explicitly anyway ✓... Actually default `sm_config_set_wrap` in default config sets wrap to program's entry? It sets wrap_target=offset+0? wrap=offset+size−1: this means PC would wrap at last instruction — but our last instruction IS `jmp start` — so even default wrap coincides ✓. Instruction encoding check for `set x, 16`: SET operand range 0–31 ✓ (u(5)). `set pins, 0/1`: source=0 (pins) ✓. One more PIO check: sideset `side 0` on `out pins, 1` — side applied simultaneously with out ✓ same cycle: DIN changes while BCK low ✓. And LRCK `set pins, 1` occurs 1 cycle after last left latch: BCK low ✓. Initial: first frame's LRCK = 0 (set pins 0) ✓. DAC compatibility: MAX98357A requires 16-48kHz sample rates & standard I2S ✓ (48k ✓), it ignores small BCK gaps ✓. Now think about "novel creative" narrative once more. Components: 1. Custom 3-wire PIO I2S transmitter (no external audio library). 2. Dual-core: core0 = deterministic audio render; core1 = UI/attractant... 3. The synth concept: **"Strange Attractor Synth"** — a Lorenz attractor is the composer AND the timbre engine: - Drone: 2-op FM whose carrier freq, modulator ratio, and brightness follow attractor coordinates. - Plucks: KS string voices; the ATTRACTOR picks pentatonic notes from its own state. - Feedback: each pluck kicks the attractor (x += note offset) → melody influences drone evolution. A music-generating ODE. 4. Interaction: pluck button, mode/sweep button, chaos pot, serial commands, ghost self-play. I think that's strong and genuinely creative. Also should provide wiring summary & build instructions. And make code compile-safe. Let me now also double check a few remaining API details: - `pico_generate_pio_header(chaosynth ${CMAKE_CURRENT_LIST_DIR}/i2s_out.pio)` ✓ generates `i2s_out.pio.h`. - In C: `#include "i2s_out.pio.h"` ✓ — needs `hardware/pio.h` included before? The generated header includes `hardware/pio.h`? It includes "pio.h"? It includes ``? Generated header includes "hardware/pio.h" ✓ I believe. Include anyway before it. - `pio_add_program` returns uint ✓. - `pio_claim_unused_sm(pio, true)` ✓. - `irq_set_exclusive_handler` ✓ from hardware/irq.h. - `dma_channel_get_irq0_status(channel)` — hmm let me double check name... In SDK 2.x, `hardware/dma.h`: `dma_channel_get_irq0_status(uint channel)` — I'm now second-guessing; I recall it was added in SDK 1.5.0 alongside `dma_channel_acknowledge_irq0/1`. Hmm, `dma_channel_acknowledge_irq0` I'm sure exists. For status, alternative guaranteed-old API: `dma_hw->intr` read + `dma_hw->ints0 = bits` to clear. To be maximally compatible, use raw registers: ```c void dma_isr() { uint32_t pending = dma_hw->intr; dma_hw->ints0 = pending; // clear flags if (pending & (1u<ints0` write clears (W1C) ✓ (RP2040 & RP2350 both have ints0 W1C ✓). `dma_hw->intr` read-only shows pending ✓. This avoids SDK version issues. Use this. (`dma_hw` from hardware/dma.h ✓.) Hmm wait, on RP2350 `dma_hw->ints0` — RP2350 DMA irq regs: `ints0`, `ints1`, and also `intr` ✓ same layout (RP2350 adds ints2/ints3). ✓. - `dma_channel_start(ch)` hmm: to start channel configured with trigger=false: `dma_channel_start(uint channel)` exists ✓ (sets trigger? starts transfer). Actually `dma_channel_start` triggers the channel ✓. But careful: for RP2350 there's `dma_channel_start` still ✓. - Config: `dma_channel_config cc = dma_channel_get_default_config(ch);` `channel_config_set_...` macros ✓. `channel_config_set_chain_to(&cc, other)` ✓. `channel_config_set_dreq(&cc, dreq)` ✓. `channel_config_set_read_increment(&cc, true)` / `set_write_increment(&cc,false)` ✓. `channel_config_set_transfer_data_size(&cc, DMA_SIZE_32)` ✓. - `dma_channel_configure(ch, &cc, &pio->txf[sm], g_audio[0], FRAMES_PER_BLOCK, false)` ✓. - ADC: `adc_init()`, `adc_gpio_init(26)`, `adc_select_input(0)`, `adc_read()` ✓ all standard. - `getchar_timeout_us(0)` — declared in pico/stdio.h? It's `getchar_timeout_us(uint32_t timeout_us)` in `pico/stdio.h`? It's actually in SDK `pico/stdio.h`? I believe `getchar_timeout_us` is in `pico/stdio.h` ✓ (used in many examples). Returns PICO_ERROR_TIMEOUT (-1) or char. - `to_ms_since_boot(get_absolute_time())` ✓ returns uint64_t. - `sleep_until`, `make_timeout_time_ms`, `delayed_by_ms` ✓ from pico/time.h via stdlib. - multicore: `multicore_launch_core1(core1_entry)` ✓. PIO header symbol: `i2s_out_program`, `i2s_out_program_get_default_config(offset)` ✓ (generated from .program i2s_out). Also `pio_sm_config` type name ✓. Pin defs: ```c #define PIN_DIN 16 #define PIN_BCK 17 #define PIN_LRC 18 ``` Consecutive 16..18 ✓ (set pindirs uses base PIN_DIN count 3). sideset base = PIN_BCK (17), set base = PIN_LRC (18), out base = PIN_DIN (16) ✓. One thing: `pio_sm_set_consecutive_pindirs(PIO pio, uint sm, uint base, uint count, bool is_out)` — base can be any pin number ✓. Wait — also need pindirs for sideset/set pins — they're within 16..18 consecutive → the single call covers all ✓. Also: before enabling, drive initial LRCK: SM starts at offset → `set pins, 0` immediately ✓. Data init: pre-render both buffers with valid audio (silence? render_block fills real audio; call twice before starting) ✓. Now let me also double check the KS `line` length vs `len`: `v->line[p+1==L ? 0 : p+1]` — fine; `KS_LINE 512`; len computed ≤ 510 ✓. KS tone freq check: len = SR/f → f=110 → 436 ✓ (frame period). The KS loop gain 65274/65536 = 0.9960 per (a+b)/2 — decay ~ f*per-pass? Typical values ✓. `v->age = SAMPLE_RATE*2` — 96k counts decremented per sample ✓ (uint32 fine). Voice trigger when note freq f: len = (uint32)(((uint64_t)SAMPLE_RATE<<32)/f)>>16: f=110<<16=7.2e6: (48000<<32)/7.2e6 = 48000*65536*... let me verify: ((SR<<32)/f)>>16 = SR<<16/f... units: SR<<32 = 48000*2^32; /f(Q16) → 48000*2^32/(110*65536) = 48000*65536/110 = 28.6M; >>16 → 436 ✓✓. Also idx = (r>>10)%11 — fine. Hmm one issue: `g_pent` stored as Q16.16 Hz ✓ used in len calc ✓. Now, excitation loop fill uses `lp` int32 — noise ±8k after >>1 — but wait I wrote `lp = (lp + n)>>1; line[i] = lp>>1;` — let me simplify: line[i] = (int16_t)(lp >> 2) — amplitude ±8k. fine. Voice output `a` int16 ±8k; vmix: vl += mulq(a, 32000) → 8k*32000>>16=3900; ✓. Also add subtle pick noise? skip. Drone: `mulq(sin_q(ph_c), 12000)` → ±6000 ✓. Plus maybe add a second detuned carrier for richness: `drone += mulq(sin_q(ph_c*2? ...)` skip — FM depth gives richness. Hmm, one concern: FM with low carrier 48-108Hz + mod ratio ~1 with depth up to ±4 cycles: output spectrum rich — good clangy drone ✓. The modulator inc ~carrier — both low freq: audible beat-rich texture ✓. The LP: mono = drone + voices; lp tracks at cutoff 300..4100 — at rho low, z low → cutoff ~300Hz → dark mellow; chaos → bright ✓ nice playable morph. `a_lp = fc * 9` where fc ≤ 4100 → 36,900 ✓ < 65536 ✓. mulq(mono−lp, a_lp) = delta*36900/65536 ≈ delta*0.56 ✓. lp_r: use different coefficient: `a2 = a_lp >> 1` (half cutoff) → lp_r lags → spectral difference → stereo width ✓. Or add slight crossfeed. Fine. DC block coeff 171 → fc ~20Hz ✓. Now the render pipeline order & variable init: lp_l/lp_r start 0 ✓; dc_l/dc_r 0 ✓; g_tick 0 ✓. `control_tick` every 128: at 48k → 375Hz; Lorenz steps 375/s with dt 0.004 → sim speed 1.5x realtime ✓. Reseed event: 'r' → core0 control: `if (g_ev_reseed) { g_ev_reseed=0; g_x = rng-ish; ...}` derive from g_tick. Also print help line at boot via core1? printf from core1 to UART — stdio mutex ✓ fine. One more potential problem: `stdio_init_all()` before `multicore_launch_core1` — core1 printf needs stdio inited ✓ done in main first. Default UART stdio on Pico 2: board `pico2` — `PICO_DEFAULT_UART 0? ` Hmm — Pico 2 board header defines default UART? The original Pico: UART0 on GP0/GP1. Pico 2: also has UART default? Pico 2 uses GP0/1 UART? Hmm — Pico 2 W? The plain Pico 2: I believe default stdio UART on GP4/GP5?? Wait: Pico (RP2040) board: UART0 = GP0/GP1 (header pins UART0 TX/RX physical 1/2). Pico 2: The RP2350 Pico 2 board ALSO uses GP0/GP1? Hmm — Pico 2 board defines `PICO_DEFAULT_UART 0`? But wait, on Pico 2 the debug... I recall Pico 2 kept GP0/1 as UART default, same as Pico. Hmm, actually there was a change: Pico 2's default UART is on GP0/GP1 still? I believe yes. And USB CDC default off unless enabled. To be safe in README: "serial on the default UART pins (GP0/GP1 at 115200) — or enable USB stdio in CMake". Fine. Actually — hmm, pico_enable_stdio_usb default 0, uart default 1 for pico2 board I'm fairly sure (board file mimics pico). OK. Also mention: to hear sound without an I2S DAC… you need one; suggest MAX98357A wiring (VIN 3V3? 5V ok, GND, DIN, BCK, LRCK, speaker out or line). Also PCM5102/UDA1334A boards. Also — safety: audio starts immediately (drone) — set initial volume modest ✓. Now assemble the full source. Also add file structure section, build instructions, wiring table, and a "how it works" explanation. Also customization tips. Let me now write final code carefully, watching for C correctness: ```c // chaosynth.c — RP2350 "Strange Attractor Synth" #include #include "pico/stdlib.h" #include "pico/time.h" #include "pico/multicore.h" #include "hardware/pio.h" #include "hardware/dma.h" #include "hardware/adc.h" #include "hardware/irq.h" #include "hardware/clocks.h" #include "i2s_out.pio.h" #define SAMPLE_RATE 48000 #define FRAMES_PER_BLOCK 64 #define CYCLES_PER_FRAME 69 // cycles in i2s_out.pio per L+R frame #define PIN_DIN 16 #define PIN_BCK 17 #define PIN_LRC 18 #define BTN_PLUCK 14 // to GND (internal pull-up) #define BTN_CHAOS 13 // hold = sweep rho #define PIN_POT 26 // ADC0: 10k pot: ends to 3V3/GND, wiper here ... ``` ISR & render in RAM: `__not_in_flash_func`. Complete code (writing it now in final form; double-check as I go): Global audio state block: ```c static PIO g_pio; static uint g_sm, g_off, g_dma[2]; static uint32_t g_audio[2][FRAMES_PER_BLOCK]; static int16_t g_sin[1024]; static int32_t g_pent[11]; static const int g_semi[11] = {0,3,5,7,10,12,15,17,19,22,24}; static volatile uint32_t g_ev_pluck, g_ev_reseed, g_rho_target; // attractor static int32_t g_x, g_y, g_z, g_rho; // per-sample state static uint16_t g_ph_c, g_ph_m; static int32_t g_inc_c, g_inc_m, g_fm_depth, g_a_lp, g_pan_l; static uint32_t g_tick; static int32_t g_lp_l, g_lp_r, g_dc_l, g_dc_r; typedef struct { int16_t line[512]; uint32_t len, pos, age; bool active; } voice_t; static voice_t g_voice[4]; static uint32_t g_voice_next; ``` `static inline int32_t mulq`, `satq` etc. ```c static inline int32_t mulq(int32_t a, int32_t b) { return (int32_t)(((int64_t)a * b) >> 16); } static inline int32_t sat1(int32_t a){ if (a > 65536) a = 65536; if (a < -65536) a = -65536; return a; } static inline int32_t softclip(int32_t x) { if (x > 20000) x = 20000 + ((x - 20000) >> 2); else if (x < -20000) x = -20000 - ((-x - 20000) >> 2); if (x > 32000) x = 32000; if (x < -32000) x = -32000; return x; } static inline int32_t sin_q(uint16_t ph) { return g_sin[ph >> 6]; } ``` lorenz: ```c static void lorenz_step(void) { const int32_t SIGMA = 10 << 16, BETA = 174762, DT = 262; // dt = 0.004 int32_t dx = mulq(SIGMA, g_y - g_x); int32_t dy = mulq(g_x, g_rho - g_z) - g_y; int32_t dz = mulq(g_x, g_y) - mulq(BETA, g_z); g_x += mulq(dx, DT); g_y += mulq(dy, DT); g_z += mulq(dz, DT); } ``` control_tick: ```c static void control_tick(void) { g_rho += (g_rho_target - g_rho) >> 12; lorenz_step(); if (g_ev_reseed) { g_ev_reseed = 0; uint32_t r = g_tick * 2654435761u; g_x = (int32_t)((r & 0xFFFF) << 8) - (1 << 23); g_y = (int32_t)(((r >> 8) & 0xFFFF) << 8) - (1 << 23); g_z = (int32_t)(((r >> 16) & 0x3FFF) << 12) + (1 << 21); } if (g_ev_pluck) { g_ev_pluck = 0; ks_trigger(); } // ---- map attractor -> audio params (all Q16.16-ish) ---- int32_t nx = sat1(mulq(g_x, 2048)); // ~ [-1, 1] int32_t ny = sat1(mulq(g_y, 2048)); int32_t nz = g_z < 0 ? 0 : (g_z > (90 << 16) ? (1 << 16) : mulq(g_z, 728)); int32_t ax = nx < 0 ? -nx : nx; int32_t f0 = 48 + ((ax * 60) >> 16); // carrier 48..108 Hz g_inc_c = ((int64_t)f0 << 16) / SAMPLE_RATE; int32_t fmod = f0 + ((f0 * ny) >> 16); // ratio 0..2x g_inc_m = ((int64_t)fmod << 16) / SAMPLE_RATE; g_fm_depth = 131072 + (g_rho >> 3); // chaos knob = FM bite int32_t fc = 300 + ((nz * 3800) >> 16); int32_t a = fc * 9; if (a > 60000) a = 60000; g_a_lp = a; int32_t p = (ny >> 1) + (1 << 15); // 0..1 g_pan_l = sat((9830 + mulq(p0, 45875)) ... ``` hmm p: ny∈[-65536,65536] → p = ny/2 + 32768 → [0,65536] ✓ Q16.16 fraction ✓. pan = 0.15 + 0.7*p: `int32_t pan = 9830 + mulq(p0, 45875);` where p0 = p (Q16.16 0..1) ✓ → pan ∈ [9830, 55730] ✓. Store g_pan_l = pan. f0 as Q?? f0 is integer Hz (48..108) ✓ plain int. `g_inc_c = ((int64_t)f0 << 16) / SAMPLE_RATE;` = f0*65536/48000 = f0*1.366 ✓ int. ks_trigger: ```c static void ks_trigger(void) { voice_t *v = &g_voice[g_voice_next++ & 3]; // the attractor composes: pick a pentatonic note from its own state uint32_t r = (uint32_t)(g_x ^ (g_y * 3) ^ (g_z * 5)) ^ (g_tick >> 6); r = (r >> 7) ^ (r << 13); uint32_t idx = (r >> 11) % 11; int32_t f = g_pent[idx]; uint32_t len = (uint32_t)((((uint64_t)SAMPLE_RATE << 32) / (uint64_t)f) >> 16); if (len < 16) len = 16; if (len > 500) len = 500; v->len = len; v->pos = 0; v->age = SAMPLE_RATE * 2; // excite the string with noise shaped by the attractor uint32_t s = r | 1; int32_t lp = 0; for (uint32_t i = 0; i < len; i++) { s ^= s << 13; s ^= s >> 17; s ^= s << 5; int32_t n = (int32_t)(s >> 16) - 32768; lp = (lp + n) >> 1; v->line[i] = (int16_t)(lp >> 2); } v->active = true; // feedback: the melody perturbs its composer g_x += (int32_t)(idx * 3000) - 15000; g_y += (int32_t)((r >> 20) & 0x3FF) - 512; } ``` Wait `(g_y*3)` int overflow fine (wraps ok, artistic). r mixes. Hmm `(uint64_t)SAMPLE_RATE << 32` — 48000<<32 huge but fits uint64 ✓ (2^32*48000 ≈ 2e14 < 2^63 ✓). Per-sample render & block: ```c static void __not_in_flash_func(render_block)(uint buf) { uint32_t *dst = g_audio[buf]; for (uint i = 0; i < FRAMES_PER_BLOCK; i++) { if ((g_tick & 127u) == 0) control_tick(); g_tick++; // --- FM drone (operator phases in Q16.16 cycles) --- g_ph_m += (uint16_t)g_inc_m; int32_t pm = mulq(sin_q(g_ph_m), g_fm_depth); g_ph_c += (uint16_t)(g_inc_c + pm); int32_t drone = mulq(sin_q(g_ph_c), 24000); // ±12000 wait: 32767*24000>>16 = 12000 ✓ // --- Karplus-Strong strings --- int32_t vl = 0, vr = 0; for (int k = 0; k < 4; k++) { voice_t *v = &g_voice[k]; if (!v->active) continue; uint32_t p = v->pos, L = v->len; int32_t a = v->line[p]; int32_t b = v->line[(p + 1) >= L ? 0 : (p + 1)]; v->line[p] = (int16_t)mulq((a + b) >> 1, 65300); // 0.9959 feedback v->pos = (p + 1) >= L ? 0 : (p + 1); if (v->age) v->age--; else v->active = false; if (k & 1) { vr += mulq(a, 30000); vl += mulq(a, 12000); } else { vl += mulq(a, 30000); vr += mulq(a, 12000); } } int32_t mono = drone + ((vl + vr) >> 1); // --- one-pole tone shaping (cutoff follows z), offset for width --- g_lp_l += mulq(mono - g_lp_l, g_a_lp); g_lp_r += mulq(mono - g_lp_r, g_a_lp >> 1); int32_t sl = g_lp_l + ((mono - g_lp_l) >> 3); int32_t sr = g_lp_r + ((mono - g_lp_r) >> 3); // --- pan drone by attractor y, add strings --- int32_t l = mulq(sl, g_pan_l) + vl; int32_t r = mulq(sr, 65536 - g_pan_l) + vr; // --- DC block (~20 Hz) --- g_dc_l += mulq(l - g_dc_l, 171); g_dc_r += mulq(r - g_dc_r, 171); l -= g_dc_l; r -= g_dc_r; int32_t l16 = softclip(l), r16 = softclip(r); dst[i] = ((uint32_t)(uint16_t)l16 << 16) | ((uint32_t)(uint16_t)r16); } } ``` Hmm `g_ph_c += (uint16_t)(g_inc_c + pm)` — g_inc_c+pm could exceed 65535 (inc 147 + pm ±250k → int32 ±249,853) → cast to uint16 wraps mod 65536 ✓ correct phase mod 1 cycle ✓. And uint16 g_ph_c addition wraps ✓. Wait drone level: drone ±12000 + strings ±(30000*8k>>16 = ±3660 each, 4 voices → ±15k) → mono up to ±27k → LP ~ same → pan mul ≤ 27k → + vl(±15k*?) wait vl includes full voice gains ±3660+1460? vl per voice 30000>>16 *8k = 3660; two voices → 7.3k... hmm voices max ±8k excite → vl ≈ ±7k. l = mulq(27k*pan≤27k) + 7k → ±34k → softclip compresses. Slightly hot but softclip handles (it's a "character" limiter). Fine — headroom mostly OK since drone typical ±6k not max. Accept — or reduce drone to 18000 (±9000) and voices 24000/10000. Let me set drone 18000 → ±9000; strings: a up to 8k, mulq(a,30000) → 3662... total maybe ±18k → softclip rarely engages ✓. OK adjust: drone = mulq(sin, 18000) → ±9000. Actually excitation `line[i] = lp>>2` → lp after smoothing ~±(32767/2)=16k, >>2 = 4k ✓ → voice output 4k*0.3 = 1.2k ×4 → quiet-ish. Hmm — plucks too quiet vs drone 9000? String energy decays from ~4k*30000/65536=1831 per active voice. Pluck loudness ~ ±3.6k sum → audible ✓ but not punchy. Bump excitation to `lp>>1` (±8k) and voice gains 40000/16000: mulq(8000*40000>>16)=4882/voice → 4 voices could hit 12k transient + drone 9k = 21k → clip headroom fine (softclip 20k rarely). OK: `line[i]=(int16_t)(lp>>1)` — careful lp ±16k → int16 fits ✓. And gains 40000 & 16000. Fine. Also add gentle excitation "burp" — nah. ISR: ```c static void __not_in_flash_func(dma_isr)(void) { uint32_t pend = dma_hw->intr; dma_hw->ints0 = pend; if (pend & (1u << g_dma[0])) render_block(0); if (pend & (1u << g_dma[1])) render_block(1); } ``` Wait — clearing via ints0 write clears ALL pending including channels whose handler... we only have our 2 ✓. Hmm — should double-check `dma_hw->ints0` field name RP2350: dma_hw has `intr`, `inte0`, `intf0`, `ints0`, plus `inte1`... ✓ (RP2350 adds more). ✓. init i2s: ```c static void i2s_init(void) { g_pio = pio0; g_sm = pio_claim_unused_sm(g_pio, true); g_off = pio_add_program(g_pio, &i2s_out_program); for (uint p = PIN_DIN; p <= PIN_LRC; p++) pio_gpio_init(g_pio, p); pio_sm_set_consecutive_pindirs(g_pio, g_sm, PIN_DIN, 3, true); pio_sm_config c = i2s_out_program_get_default_config(g_off); sm_config_set_out_shift(&c, false, true, 32); // MSB first, autopull 32 sm_config_set_out_pins(&c, PIN_DIN, 1); sm_config_set_sideset(&c, 1, false, false); sm_config_set_sideset_pins(&c, PIN_BCK); sm_config_set_set_pins(&c, PIN_LRC, 1); sm_config_set_fifo_join(&c, PIO_SM_FIFO_JOIN_TX); sm_config_set_clkdiv(&c, (float)clock_get_hz(clk_sys) / ((float)SAMPLE_RATE * CYCLES_PER_FRAME)); pio_sm_init(g_pio, g_sm, g_off, &c); } ``` Hmm — `sm_config_set_out_shift(&c, shift_right=false, ...)`: double-check the actual param name/meaning once more: `void sm_config_set_out_shift(pio_sm_config *c, bool shift_right, bool autopull, uint pull_threshold)`. RP2040 datasheet: OSR shift direction: "shift right" (SHIFTCTRL OUT_SHIFTDIR): 1 = shift right (LSB first), 0 = shift left (MSB first). SDK's `shift_right` maps directly to OUT_SHIFTDIR ✓. So false = MSB first ✓✓. Also default pull threshold: we set 32 ✓. DMA init: ```c static void dma_init(void) { g_dma[0] = (uint)dma_claim_unused_channel(true); g_dma[1] = (uint)dma_claim_unused_channel(true); for (int i = 0; i < 2; i++) { dma_channel_config cc = dma_channel_get_default_config(g_dma[i]); channel_config_set_transfer_data_size(&cc, DMA_SIZE_32); channel_config_set_read_increment(&cc, true); channel_config_set_write_increment(&cc, false); channel_config_set_dreq(&cc, pio_get_dreq(g_pio, g_sm, true)); channel_config_set_chain_to(&cc, g_dma[1 - i]); dma_channel_configure(g_dma[i], &cc, &g_pio->txf[g_sm], g_audio[i], FRAMES_PER_BLOCK, false); } } ``` Hmm: `&g_pio->txf[g_sm]` — write addr type volatile uint32_t* ✓. Note g_pio is PIO (pointer) ✓. main: ```c int main(void) { stdio_init_all(); for (int i = 0; i < 1024; i++) g_sin[i] = (int16_t)lrintf(sinf(2.0f * (float)M_PI * i / 1024.0f) * 32766.0f); for (int i = 0; i < 11; i++) g_pent[i] = (int32_t)(110.0f * powf(2.0f, g_semi[i] / 12.0f) * 65536.0f); g_x = 8 << 16; g_y = 12 << 16; g_z = 20 << 16; g_rho = g_rho_target = 24 << 16; i2s_init(); dma_init(); render_block(0); render_block(1); irq_set_exclusive_handler(DMA_IRQ_0, dma_isr); dma_channel_set_irq0_enabled(g_dma[0], true); dma_channel_set_irq0_enabled(g_dma[1], true); irq_set_enabled(DMA_IRQ_0, true); multicore_launch_core1(core1_entry); pio_sm_set_enabled(g_pio, g_sm, true); dma_channel_start(g_dma[0]); printf("chaosynth up. keys: p=pluck r=reseed (uart 115200)\r\n"); while (true) { sleep_ms(2000); printf("rho=%d x=%d y=%d z=%d (fixed*1/65536)\r\n", (int)(g_rho >> 16), (int)(g_x >> 16), (int)(g_y >> 16), (int)(g_z >> 16)); } } ``` Hmm: `dma_isr` signature for irq handler: `void (*)(void)` ✓. `irq_set_exclusive_handler` fine. core1_entry: ```c static void core1_entry(void) { gpio_init(BTN_PLUCK); gpio_set_dir(BTN_PLUCK, GPIO_IN); gpio_pull_up(BTN_PLUCK); gpio_init(BTN_CHAOS); gpio_set_dir(BTN_CHAOS, GPIO_IN); gpio_pull_up(BTN_CHAOS); adc_init(); adc_gpio_init(PIN_POT); adc_select_input(0); uint32_t pot = 0; bool last_pluck = true; uint32_t next_ghost = 4000, rng = 0x9E3779B9u; while (true) { uint32_t now = (uint32_t)to_ms_since_boot(get_absolute_time()); pot = (pot * 255u + adc_read()) >> 8; // 0..4095 smoothed uint32_t rho = (8u << 16) + pot * 592u; // 8 .. 45 (Lorenz chaos > ~24!) if (!gpio_get(BTN_CHAOS)) { // hold: auto-sweep the bifurcation rho = (8u + ((now >> 9) % 37u)) << 16; } g_rho_target = (int32_t)rho; bool plk = !gpio_get(BTN_PLUCK); if (plk && !last_pluck) g_ev_pluck = 1; last_pluck = plk; if (now > next_ghost) { // it plays itself... g_ev_pluck = 1; rng ^= rng << 13; rng ^= rng >> 17; rng ^= rng << 5; next_ghost = now + 3000 + (rng & 0x1FFF); } int c = getchar_timeout_us(0); if (c == 'p' || c == ' ') g_ev_pluck = 1; if (c == 'r') g_ev_reseed = 1; sleep_ms(5); } } ``` Note: buttons pressed = low ✓. pot*592: 4095*592=2.4M + 524k = 2.9M = 45<<16 ✓ (45*65536=2.95M ✓). Debounce: 5ms poll + edge → maybe bounce; add simple: require two consecutive reads? Minor; sleep 5 + edge on raw is mostly fine. Could add `if (plk && !last_pluck)` with 10ms poll. Fine. Now the PIO file (final): ```pio ; ; chaosynth — 3-wire I2S master for RP2350 (works on RP2040 too) ; ; GP16 -> DIN GP17 -> BCK GP18 -> LRCK ; ; Standard 16-bit stereo Philips I2S: MSB-first, data shifts out on ; BCK falling edge (side 0), DAC latches on BCK rising edge (side 1). ; LRCK is driven by the SET pin group. ; .program i2s_out .side_set 1 start: set pins, 0 side 0 ; LRCK low -> left set x, 16 side 0 bitloop_l: out pins, 1 side 0 ; DIN = MSB..LSB, BCK low jmp x-- bitloop_l side 1 ; BCK high: DAC clocks the bit set pins, 1 side 0 ; LRCK high -> right set x, 16 side 0 bitloop_r: out pins, 1 side 0 jmp x-- bitloop_r side 1 jmp start side 0 ``` Wait — `set pins, 0 side 0` — SET group is 1 pin; but hmm: `set pins, 0` — the SET instruction with 2-bit? `set pins, 0` writes 0 to 1 configured pin ✓. One more check: 32 bits consumed per frame exactly ✓ (16+16) — autopull threshold 32 ✓ alignment: every `out` pulls bits from current OSR; at frame boundary OSR exactly empty → next out pulls next word ✓. But WAIT — subtle: with autopull and pull_threshold 32, the pull happens when the shift counter reaches 32, i.e., after the 32nd shift... but WHICH instruction triggers the refill — the NEXT out (32nd+1)? The 32 outs of a frame: bits 31..0 shifted out; after bit0 shifted, OSR empty; the next `out` (first bit of next frame) performs pull (stalling if FIFO empty) then outputs new MSB ✓✓. Also autopull happens automatically — but does the pull occur DURING the out instruction before shifting ✓ (yes: pull then shift). DMA delivers 32-bit frames; format (L<<16)|R ✓ with MSB-first: first 16 bits out = bits 31..16 = L ✓ matches LRCK=left-first ✓✓. Now — CMakeLists.txt: ```cmake cmake_minimum_required(VERSION 3.13) # standard pico-sdk bootstrap set(PICO_SDK_PATH $ENV{PICO_SDK_PATH}) # or set explicitly include(${PICO_SDK_PATH}/pico_sdk_init.cmake)? ``` Standard: ```cmake cmake_minimum_required(VERSION 3.13) include(pico_sdk_init.cmake)? ``` Actual canonical template: ```cmake cmake_minimum_required(VERSION 3.13) include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake) # or pico_sdk_init... project(chaosynth C CXX ASM) set(CMAKE_C_STANDARD 11) pico_sdk_init() add_executable(chaosynth chaosynth.c) pico_generate_pio_header(chaosynth ${CMAKE_CURRENT_LIST_DIR}/i2s_out.pio) target_link_libraries(chaosynth pico_stdlib pico_multicore hardware_pio hardware_dma hardware_adc hardware_irq hardware_clocks ) pico_add_extra_outputs(chaosynth) # pico_enable_stdio_usb(chaosynth 1) # optional: USB CDC console ``` pico_sdk_import: canonical top lines: ```cmake cmake_minimum_required(VERSION 3.13) # pull pico-sdk (set PICO_SDK_PATH or place next to project) include(${PICO_SDK_PATH}/pico_sdk_init.cmake) # hmm ``` The usual template is: ```cmake cmake_minimum_required(VERSION 3.13) include(pico_sdk_init.cmake)? ``` No — official: `include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)` then `project(...)`, `pico_sdk_init()`. Yes, pico_sdk_import.cmake lives in pico-sdk/external/. I'll use env var form with comment. Note: `pico_stdlib` already includes pico_multicore? pico_stdlib links pico_runtime, hardware stuff — but explicit listing is safe. Also need `pico_enable_stdio_usb`? default off; UART default on for pico2 board (I'm fairly confident Pico 2 keeps UART0 default stdio? Hmm — wait, actually I now recall Pico 2's default stdio... the pico2 board header: `#define PICO_DEFAULT_UART 0`? Pico 2 board: GP0/GP1 UART? RP2350 Pico2 board uses UART0 on GPIO 0/1? I believe yes, same as Pico. OK.) Hmm, one thing to double check: `lrintf`/`sinf`/`powf` — libm linked: pico_sdk_init links `pico_stdlib` → includes m? pico_platform... The SDK by default links libm? Hmm. In pico projects I've seen people use sinf without adding -lm... pico-sdk's `pico_standard_link` links `m`? I believe yes (the SDK links libm by default — `target_link_libraries(pico_standard_link ... m?)`. Hmm not 100%. To be bulletproof, avoid powf: compute pentatonic by successive multiplication: 2^(1/12) fixed: 12th root of 2 = 1.0594631 Q16 = 69476? Hmm 1.0594631*65536 = 69475.9 → iterate 12× per note: f *= Q: do with mulq: f_q = 110<<16; for each semitone step: f_q = mulq(f_q, 69476)... rounding drift ok. Or just hardcode the 11 frequencies as ints: compute at compile time manually: 110.0 *2^(0/12)=110.0 → 110<<16 3/12: 110*1.1892=130.81 → 130<<16 + .81*65536≈857800... let me just hardcode float literals — but need powf at compile? They're literals: 130.81 etc. So: ```c static const float pent_f[11] = {110.0f, 130.81f, 146.83f, 164.81f, 196.00f, 220.00f, 261.63f, 293.66f, 329.63f, 392.00f, 440.00f}; g_pent[i] = (int32_t)(pent_f[i] * 65536.0f); ``` Float multiply at runtime (no libm needed for multiply!) ✓. But sinf/lrintf still needed for sin table. Alternatives: build sin table via incremental oscillator? Could generate with complex rotation (no libm): e^jω recurrence: re,im; ω=2π/1024: use float cos/sin initial values... needs cosf anyway. Recurrence drifts. Simplest: keep sinf/lrintf — I'm now recalling: pico-sdk DOES link libm: in `pico_standard_link`... Actually the SDK toolchain wraps newlib with math via `libm` in libstdc++/newlib — linking `m` explicitly: `target_link_libraries(chaosynth m)` — harmless even if redundant! Add `m` to be safe ✓. Actually pico examples using sin: e.g., `audio examples`, `fft`... I'm confident it works; adding m explicitly is belt & braces. Hmm also `M_PI`: defined in math.h with __USE_MISC? On GCC arm-none-eabi, M_PI available unless strict ANSI. Safe: define fallback `#ifndef M_PI #define M_PI 3.14159265358979f #endif`. Also `(uint16_t)g_inc_m` — g_inc_m int32 ~ up to 295 ✓ fits. Also unused warnings fine. Double-check `softclip` overflow: x up to ±30k; (x−20000)>>2 fine ✓. l up to maybe ±40k worst → softclip → 20000+(20000>>2)=25000 → then clamp 32000 → fine int16 ✓. Check `sat1` usage: mulq(g_x, 2048): g_x ≤ ±(35<<16)=±2.3M; *2048 = 4.7e9 → int64 → >>16 = 7.2e4?? Wait mulq(2.3M, 2048) = 2.3M*2048/65536 = 72,000 → that's 1.096 in Q16.16 → sat1 clamps to 65536 ✓. OK values with |g_x| ≤ 32*65536=2.1M → nx ≤ 65,536 ✓ exactly ≤1 ✓. `ny >> 1 + (1<<15)`: ny ∈[-65536,65536] → p = ny>>1 (±32768) + 32768 → [0, 65536] ✓. `pan = 9830 + mulq(p, 45875)` → mulq(65536,45875)=45,875 → pan ∈ [9830, 55705] ✓ Q16 ✓. `65536 - g_pan_l` ✓ ≥ 9831 ✓. LP: `g_lp_l += mulq(mono - g_lp_l, g_a_lp)` — a up to 60000 → delta*0.915 ✓ stable ✓. `g_a_lp >> 1` → 30000 max ✓ stable ✓. DC: mulq(...,171) → 0.0026 ✓ stable ✓. Lorenz ranges with rho up to 45: |x|≤~35, y ≤ ~45, z ≤ ~90: Q16.16 fits ✓; internal products: g_x*(g_rho − g_z): 2.3M * (2.95M−5.9M=−3M) → int64 −7e12 ✓ >>16 = −1.06e8 ✓ int32 ✓. mulq(BETA, g_z)= 174762*5.9M = 1e12 ✓ >>16 = 1.6e7 ✓. dz = mulq(g_x,g_y)=2.3M*2.9M=6.9e12>>16=1.05e8 ✓. mulq(dz,DT=262): 1.05e8*262=2.7e10 >>16=4.2e5 = 6.4 units ✓ fine. g_rho lerp `>>12` at 375Hz → time constant ~ 17ms? (1/2^12 per tick *375) → ~ 10ms — snappy param ✓ fine. Now — the print in main loop uses int division of negative Q — g_x>>16 arithmetic shift ✓ prints signed value ✓. One more consideration — **boot silence**: pre-rendered blocks contain drone immediately ✓ desired (it starts droning). Maybe fade-in? g_tick could drive initial gain ramp: add `g_age++` → master gain ramp first second: `int32_t master = g_warm < 48000 ? (g_warm<")))`. Usage: `__not_in_flash_func(static void render_block(uint buf)) {...}` — typical usage in pico code: `void __not_in_flash_func(foo)(void)` hmm. The attribute must precede the declarator: `static void __not_in_flash_func(render_block)(uint buf)` — used in pico examples as: `static void __not_in_flash_func(handle_transfer)()`. Hmm — attribute between `void` and `(name)`? GCC allows `int __attribute__((section("foo"))) func(void)`; also `__attribute__((...)) void func` — macro expands to attribute string placed after `void`? `static void __not_in_flash_func(render_block)(uint buf)` → `static void __attribute__((noinline,...))(render_block)(uint buf)`?? That's wrong — macro takes fn as arg: `__not_in_flash_func(render_block)` → `__attribute__((...)) render_block`?? Let me recall actual pico usage: in pico-examples `void __not_in_flash_func()...` e.g.: ```c static void __not_in_flash_func(audio_irq)() { ... } ``` Yes! That's the canonical form: `static void __not_in_flash_func(audio_irq)() {}` — the macro wraps the function NAME: `#define __not_in_flash_func(func_name) __attribute__((noinline)) func_name`? Hmm — actual definition in pico/platform.h: ```c #define __not_in_flash_func(x) __attribute__((noinline)) x ``` no wait... I recall: `#define __not_in_flash_func(x) __not_in_flash_func_impl`? The real one: ```c #define __not_in_flash_func(x) __attribute__((noinline, section(".time_critical." #x))) x ``` Hmm — with stringification, so `static void __not_in_flash_func(render_block)(uint buf)` expands to `static void __attribute__((noinline, section(".time_critical.render_block")))(render_block)(uint buf)`?? That wouldn't compile... Actually stringize: `section(".time_critical." #x)` — x=render_block → `section(".time_critical.render_block")`. Expansion: `static void __attribute__((noinline, section(".time_critical.render_block"))) render_block(uint buf)` — wait the macro arg x is the whole function name including... `__not_in_flash_func(render_block)(uint buf)`: macro consumes `render_block`, leaves `(uint buf)` outside → expansion `__attribute__((...)) render_block` then `(uint buf)` → `static void __attribute__((noinline, section("..."))) render_block(uint buf)` ✓ valid C ✓✓. Great — canonical usage ✓. And `__time_critical_func(x)` = `__not_in_flash_func(x)` with different section ✓ same usage pattern. I'll use `__time_critical_func` for render_block and the ISR (both need low latency / RAM execution). Careful: `__time_critical_func` may place function in .data (copy at boot) — for ISR called before... called only after boot ✓. Another check: `dma_isr` registered via irq_set_exclusive_handler — runs in IRQ mode; uses our functions ✓. Also `irq_set_priority(DMA_IRQ_0, 0xF0)`? default fine. Also: disable unused `stdio` from ISR ✓. One more check: `printf` inside main while-loop while core1 sleeps — stdio thread-safe ✓. Also the initial `render_block` calls happen BEFORE `g_warm` increment inside — g_warm global init 0 ✓. Add `g_warm` usage: ```c int32_t wg = (g_warm < SAMPLE_RATE) ? (int32_t)mulq1? : ``` compute: `uint32_t w = g_warm++; int32_t wg = w >= SAMPLE_RATE ? 65536 : (int32_t)((w * 65536) / SAMPLE_RATE);` w*65536 up to 3.1e9 → use uint64 or compute (w<<16)/48000: w≤48000 → w<<16 = 3.1e9 → overflow uint32? 48000*65536 = 3.1e9 < 4.29e9 ✓ fits uint32 barely ✓ (max w=47999 → 3.147e9 ✓). Use uint32: `int32_t wg = w >= (uint)SAMPLE_RATE ? 65536 : (int32_t)(((uint32_t)w << 16) / SAMPLE_RATE);` ✓. Then `l = mulq(l, wg); r = mulq(r, wg);` ✓. OK. Also one potential compile warning: `mulq(g_x, 2048)` etc fine. In ks_trigger, `(g_x ^ (g_y*3) ^ (g_z*5))` — signed int overflow UB technically — use unsigned casts: `(uint32_t)g_x ^ ((uint32_t)g_y * 3u) ^ ((uint32_t)g_z * 5u)` ✓. Also `g_x += (int32_t)(idx * 3000) - 15000;` idx uint32*3000 ✓. Also `r = (r >> 7) ^ (r << 13);` uint ops ✓. Alright, also check `voice_t line[512]` — len clamp 500 ✓ and `(p+1)>=L` bounds ✓. `v->line[p] = (int16_t)mulq((a+b)>>1, 65300);` a,b int16 → sum ±65k → >>1 ±32k; mulq(32k, 65300) = 32k*0.9967=31.9k ✓ fits int16? 31900 < 32767 ✓. Edge: excitation values ±(lp>>1) where lp ±16k → ±8k ✓. Decay: 65300/65536 = 0.99666 per sample-tap — per period decay = 0.99666^len — len 436 → 0.23 per period → fast-ish decay (per 9ms period ×0.23 → -12dB per 9ms → decays to nothing in ~40ms?? TOO FAST? wait: 0.99666^436 = e^(−436*0.00334) = e^−1.455 = 0.23. So each loop round the string loses 77%?? Hmm that means amplitude ×0.23 per period → after 2 periods 5%, after 3 periods ~1% → ~30ms tail — too plinky! Standard KS: per-sample feedback with averaging gives 0.5 damping? The averaging (a+b)/2 already loses HF; the loop gain 0.9966 adds LF decay: time constant = 1/(1−0.99666) ≈ 300 samples ≈ 6ms?? No wait: per-sample gain applies once per sample as the wave passes: amplitude after t samples = 0.99666^t → τ = 1/0.00334 ≈ 300 samples = 6.3ms. WAY too fast — string dies in ~20ms. Hmm — standard KS uses loop gain ~0.996–0.999 with the loss applied per DELAY-LINE sample: feedback factor ρ = 0.996 → decay per period = ρ^len: with len 436: 0.996^436 = e^(−436*0.004) = e^−1.75 = 0.17 — hmm still decays quickly?? But classic KS plucks last ~1s. Let me reconsider: classic KS decay: they use ρ ≈ 0.99...0.999 and note decay time. For a 440Hz note (len=100 @44.1k): 0.996^100 = 0.67 per period → 3dB per 2 periods? 440 periods/s → decays to 1% after ln(0.01)/ln(0.67) ≈ 17 periods = 39ms?? Hmm but real KS plucks sound like ~0.5-2s. Real implementations: ρ=0.995..0.999 → for len 100: 0.999^100=0.905 → τ = 1/(−ln 0.905)/period... 0.905 per period → 1% at 100 periods ≈ 0.23s. With ρ=0.9995: 0.951 per period → 1% at 900 periods ≈ 2s. OK so ρ should be ~0.9995 for nice sustain, i.e., per-sample fb = 65536−33 ≈ 65503. And the averaging filter adds its own decay on HF only. So set fb = 65520 (0.99951): per period 0.99951^len: len 436 → 0.81 → τ ≈ 5 periods ≈ 45ms?? wait: 0.99951^436 = e^(−436*0.00049) = e^−0.214 = 0.81 per period (period= len/48000 = 9ms) → 20% loss per period → −1dB/9ms → −60dB at ~0.5s ✓ decent pluck tail (~0.5-1s). Use fb ≈ 65520. For higher notes shorter len → slower per-period decay ✓ natural ✓. So `v->line[p] = (int16_t)mulq((a+b)>>1, 65520);` — hmm but pure KS with gain ~1 and averaging can ring very long; age kill at 2s ✓. Also voice gain: excite ±8k → voice out ±8k*0.46 (gain 30000/65536=0.458) ≈ ±3.7k per voice ✓. OK. Also damping of drone reverb? skip. Now finalize numbers in code and write the answer. Also add small注释 for tweaking. One more sanity check on PIO sideset pin base vs OUT base overlapping? No overlap (16 vs 17 vs 18 distinct) ✓. Also: must make sure `sm_config_set_out_pins(&c, PIN_DIN, 1)` — out base 16 count 1 ✓. Also — `pio_gpio_init` for each pin ✓. Also: `gpio_set_function`? Not needed — pio_gpio_init handles ✓. Also, DMA channel numbers: claim before configure ✓. Also, note `g_dma` type uint — dma_claim returns int (could be −1). Cast ✓. Also check: `pio_get_dreq(g_pio, g_sm, true)` ✓. Also, C standard: `for (uint i = 0; ...)`, mixed decls — C11 ✓. Final check on `dma_isr` name colliding with macros — fine. Also, `irq_set_exclusive_handler(DMA_IRQ_0, dma_isr);` — dma_isr must be `void dma_isr(void)` ✓ and `__time_critical_func(dma_isr)` form: `static void __time_critical_func(dma_isr)(void)` — wait the macro usage: `static void __time_critical_func(dma_isr)(void)` → expands `static void __attribute__((...)) dma_isr(void)` ✓. Hmm, one thing — with `irq_set_exclusive_handler`, function runs in RAM ✓. Also the status print divides Q values — fine. Also `printf` of `%d` with casts ✓. Also core1_entry declared before main and referenced — define `static void core1_entry(void)` before main ✓ (multicore_launch_core1 takes fn ptr ✓). Potential warning: `lrintf` with -O2 needs `-ffast-math`? No, works ✓. Let me also reconsider: do I want `stdio_init_all()` before ADC init on core1 — fine. Also — important: the pot read on core1 while... no conflict ✓. Also: `g_rho_target` volatile int32_t ✓. One more: `while (1)` in core1 with sleep_ms(5) — if BTN_CHAOS held: `now>>9 % 37` cycles 8..45 every 524ms/step — sweep period ~19s ✓ nice slow morph. Also ghost timing: `next_ghost` init 4000 ✓. Also — `getchar_timeout_us(0)` needs stdio inited ✓. I think the code is solid. Also provide alternative: change `SAMPLE_RATE` to 44100 etc. Also mention RP2350-specific: dual M33 cores used; note works on RP2040 (Pico 1) unchanged except clk (125MHz auto-handled by clock_get_hz ✓). Nice. Also — I should double check `pio_sm_set_consecutive_pindirs` argument order once more: `pio_sm_set_consecutive_pindirs(PIO pio, uint sm, uint pins_base, uint pin_count, bool is_out)` — I stated base then count then bool ✓. Hmm, actual: `static void pio_sm_set_consecutive_pindirs(PIO pio, uint sm, uint pins_base, uint npins, bool is_out)` ✓ yes. Also `sm_config_set_set_pins(&c, PIN_LRC, 1)` ✓. Also, careful: SET pin group with `set pins, 1` — writes bit0 → base pin ✓ 1 pin ✓. Also make sure LRCK pin starts LOW before SM runs — SM's first instruction sets it ✓ but before that it's default 0? After pindirs set, output register value 0 → LRCK low ✓ fine. Double-check `dma_channel_get_default_config` returns config struct ✓. Now, are there any issues with `channel_config_set_chain_to` needing the other channel configured first? No — chain is just a number in config ✓. Also: when ch0 completes → triggers ch1 → ch1 was configured trigger=false (armed? chain trigger starts it) ✓. Also: IRQ enable order: enabling channel IRQ before handler install would be bad; order: install handler, enable IRQs per channel, enable NVIC ✓ as in main. Alright. One more think about divider float: `(float)clock_get_hz(clk_sys) / ((float)SAMPLE_RATE * CYCLES_PER_FRAME)` → 150e6/(48000*69)= 45.2899 → sm_config_set_clkdiv ✓ (max divider 65536 ✓). Let me also reconsider whether BCK idle-low gaps matter for MAX98357A — it handles 16..48kHz LRCK; fine. I2S 16-bit: MAX98357A: yes ✓. PCM5102: supports 16 ✓. Also — "left" channel goes out first with LRCK low ✓ (Philips: WS=0 → left ✓). Now, also double check `sm_config_set_out_shift` param: signature `(pio_sm_config *c, bool shift_right, bool autopull, uint pull_threshold)` ✓. And in the generated header — nothing else needed. Also check: `pio->txf[g_sm]` type: `volatile uint32_t txf[4]` ✓ address-of ✓. Also — `#include "hardware/clocks.h"` for clock_get_hz ✓ (also pulled by stdlib? explicit ✓). Also `pico/multicore.h` for launch ✓. pico_multicore library linked ✓. `hardware/adc.h` + hardware_adc ✓. Now write everything out. Also add usage/serial note: "p" plucks, "r" reseeds. Also I realize: `g_warm` increments per sample inside render (not in control tick) — define `static uint32_t g_warm;` ✓ increment every sample: `uint32_t w = g_warm; if (g_warm < (uint32_t)SAMPLE_RATE) g_warm++;` then wg compute ✓. Also, initial `printf` before SM started — fine. Let me also present estimated CPU: ~8% core0. Good. Also — one more important double-check: **`out pins, 1` uses OUT pin group base = PIN_DIN with count 1** — but ALSO note PIO requires `sm_config_set_out_pins` ✓ done. What about `autopull` stalling the SM with `pull_threshold=32` — wait, actually threshold semantics: pull_threshold = number of bits shifted out before autopull refills = 32 ✓ full word ✓. Also — since every frame consumes exactly 32 bits and DMA delivers 32-bit words — OSR refills at frame boundaries ✓. But — IMPORTANT: what if SM starts pulling BEFORE DMA started (we start DMA after SM enable — SM runs immediately, first `out` stalls waiting FIFO; DMA then feeds) ✓ no misalignment (FIFO pops are in order) ✓. Now, format of answer: intro (what/why creative), wiring, three code files, build, playing guide, extension ideas. Keep reasonably concise but complete. The code is the star. Let me also double check pentatonic array values: semis [0,3,5,7,10,12,15,17,19,22,24]: 110 * 2^(0)=110; 3:130.81 ✓ (minor third 1.1892×110=130.8 ✓); 5: 146.83 ✓ (perfect 4th 1.3348×110=146.8 ✓); 7: 164.81 ✓ (fifth 1.4983×110=164.8 ✓); 10: 196.0 ✓ (min7 1.7818×110=196 ✓); 12: 220 ✓; 15: 261.6 ✓; 17: 293.66 ✓; 19: 329.6 ✓; 22: 392 ✓; 24: 440 ✓. A-minor-pentatonic across 2 octaves ✓. Also — scale index picks from attractor: `(r >> 11) % 11` — distribution whatever, fine. One last code-flow check in `control_tick`: it's called from render_block which is in time-critical — fine. Also declare prototypes order: put helper functions before render_block; control_tick & ks_trigger before control_tick? ks_trigger used by control_tick → define ks_trigger before control_tick ✓. mulq etc before ✓. Also `sat1` before use ✓. Also unused `sat1` result types fine. Also — compile check: `mulq(g_z, 728)` where g_z ≤ 90<<16: mulq → 90*728 = 65,520 ✓ ≈ 1.0<<16 ✓. `g_a_lp = fc*9`: fc=300..4100 → 2700..36900 ✓. Also in render: `g_lp_r += mulq(mono - g_lp_r, g_a_lp >> 1);` — fine. Also add slight stereo shimmer: skip. Also — pan in stereo: `l = mulq(sl, g_pan_l) + vl;` — note mulq(sl, pan) reduces level when centered (pan 0.5 → −6dB) fine. Write final answer now. Also include note: "tested pattern follows pico-examples conventions; build with pico-sdk 2.x". Also the user said "Write novel creative code for a Rp2350 that creates a synthiziser when passed to i2s" — "when passed to i2s" meaning the audio data is passed to I2S. ✓ our design. Length: sizeable but okay. Include all three files fully. Add wiring diagram ASCII small. Let me write out the final code in full, one more careful pass for syntax as I "type" it: ```c /** * chaosynth.c — “LORENZ” — a strange-attractor synthesizer for RP2350 (Pico 2) * ... */ #include #include #include "pico/stdlib.h" #include "pico/multicore.h" #include "hardware/pio.h" #include "hardware/dma.h" #include "hardware/adc.h" #include "hardware/irq.h" #include "hardware/clocks.h" #include "i2s_out.pio.h" #ifndef M_PI #define M_PI 3.14159265358979323846 #endif #define SAMPLE_RATE 48000 #define FRAMES_PER_BLOCK 64 #define CYCLES_PER_FRAME 69 #define PIN_DIN 16 #define PIN_BCK 17 #define PIN_LRC 18 #define BTN_PLUCK 14 #define BTN_CHAOS 13 #define PIN_POT 26 ``` state... I'm confident in the design. Also mention in comments: works on RP2040 too. Final answer structure: - Concept blurb - Wiring - i2s_out.pio - chaosynth.c - CMakeLists.txt - Build & play - Sound design notes / hacks Go. # LORENZ — a "strange attractor" synth for the RP2350 **The idea:** instead of oscillators and envelopes, the entire instrument *is* a Lorenz attractor (the butterfly-shaped chaotic ODE). The attractor's (x, y, z) state is integrated on-core in Q16.16 fixed point and mapped live onto an FM drone: **x → carrier pitch, y → modulator ratio & pan, z → filter brightness**. The same attractor *composes*: every pluck is a Karplus-Strong string whose pentatonic note is chosen from the attractor's own state, and every pluck **kicks the attractor back** — so the melody and the timbre mutate each other in a feedback loop. A pot sweeps ρ (the bifurcation parameter): below ρ≈24 the drone is laminar and dull, above it the whole machine goes chaotic and clangorous. Core 0 renders audio deterministically into DMA ping-pong buffers; core 1 handles all UI. No external audio library — I2S is a hand-rolled 9-instruction PIO state machine. ## Wiring | I2S DAC (MAX98357A / PCM5102 / UDA1334) | Pico 2 | |---|---| | DIN | GP16 | | BCK | GP17 | | LRC | GP18 | | GND / VCC | GND / 3V3 (or 5V) | | Control | Pico 2 | |---|---| | Button "pluck" → GND | GP14 (internal pull-up) | | Button "chaos sweep" (hold) → GND | GP13 | | 10k pot wiper (ends → 3V3 & GND) | GP26 (ADC0) | Serial console on the default UART (115200): `p` = pluck, `r` = re-seed the attractor. It also "ghost plays" plucks by itself if you leave it alone. ## `i2s_out.pio` — hand-rolled I2S master ```pio ; ; chaosynth — 3-wire I2S master for RP2350 (also runs on RP2040) ; ; out pin group -> GP16 (DIN) ; side-set pin -> GP17 (BCK) [1 side bit: BCK level] ; set pin group -> GP18 (LRCK) ; ; Philips I2S, 16-bit stereo, MSB first. Data changes while BCK is ; low (side 0); the DAC latches on the rising edge (side 1). ; One stereo frame = 69 SM cycles -> sample rate is set by clkdiv. ; .program i2s_out .side_set 1 start: set pins, 0 side 0 ; LRCK low -> left channel set x, 16 side 0 bitloop_l: out pins, 1 side 0 ; DIN = next bit, MSB first jmp x-- bitloop_l side 1 ; BCK high: DAC clocks it in set pins, 1 side 0 ; LRCK high -> right channel set x, 16 side 0 bitloop_r: out pins, 1 side 0 jmp x-- bitloop_r side 1 jmp start side 0 ; 16+16 bits = exactly one 32-bit ; OSR word -> autopull keeps frames ; perfectly aligned forever ``` ## `chaosynth.c` ```c // --------------------------------------------------------------------------- // LORENZ — strange-attractor synthesizer for the Raspberry Pi Pico 2 (RP2350) // // core 0: deterministic audio renderer -> DMA ping-pong -> PIO I2S // core 1: UI (buttons, pot, UART, ghost autoplay) // // Sound engine (all Q16.16 fixed point, no floats in the audio path): // * Lorenz attractor dx=s(y-x), dy=x(rho-z)-y, dz=xy-bz, integrated at 375 Hz // * 2-op FM drone: x -> carrier freq, y -> mod ratio + pan, rho -> FM bite // * one-pole tone filter whose cutoff follows z (the "butterfly's height") // * 4 Karplus-Strong plucked strings; the ATTRACTOR picks pentatonic notes // from its own state, and each pluck perturbs the attractor in return // (the composition edits its composer). // --------------------------------------------------------------------------- #include #include #include "pico/stdlib.h" #include "pico/multicore.h" #include "hardware/pio.h" #include "hardware/dma.h" #include "hardware/adc.h" #include "hardware/irq.h" #include "hardware/clocks.h" #include "i2s_out.pio.h" #ifndef M_PI #define M_PI 3.14159265358979323846 #endif #define SAMPLE_RATE 48000 #define FRAMES_PER_BLOCK 64 // 1.33 ms per DMA ping-pong buffer #define CYCLES_PER_FRAME 69 // cycles per L+R frame in i2s_out.pio #define PIN_DIN 16 // I2S: DIN, BCK, LRC must be consecutive #define PIN_BCK 17 #define PIN_LRC 18 #define BTN_PLUCK 14 // button to GND, internal pull-up #define BTN_CHAOS 13 // hold to auto-sweep rho #define PIN_POT 26 // ADC0: 10k pot, wiper here // ------------------------------- shared state ------------------------------ static volatile uint32_t g_ev_pluck; // core1 -> core0 event mailboxes static volatile uint32_t g_ev_reseed; static volatile int32_t g_rho_target; // core1 -> core0 parameter static PIO g_pio; static uint g_sm, g_off; static uint g_dma[2]; static uint32_t g_audio[2][FRAMES_PER_BLOCK]; static int16_t g_sin[1024]; // full-period sine, Q15 amplitude static int32_t g_pent[11]; // A-minor pentatonic, 2 octaves, Q16 Hz static const int g_semi[11] = {0,3,5,7,10,12,15,17,19,22,24}; static const float g_pentf[11] = {110.f,130.81f,146.83f,164.81f,196.f, 220.f,261.63f,293.66f,329.63f,392.f,440.f}; // attractor (Q16.16) static int32_t g_x, g_y, g_z, g_rho; // per-sample audio state static uint16_t g_ph_c, g_ph_m; // FM phase (uint16 wraps = free mod 2pi) static int32_t g_inc_c, g_inc_m; // phase increments per sample static int32_t g_fm_depth, g_a_lp, g_pan_l; static int32_t g_lp_l, g_lp_r, g_dc_l, g_dc_r; static uint32_t g_tick, g_warm; typedef struct { int16_t line[512]; // Karplus-Strong delay line uint32_t len, pos, age; bool active; } voice_t; static voice_t g_voice[4]; static uint32_t g_voice_next; // ------------------------------- tiny helpers ------------------------------ static inline int32_t mulq(int32_t a, int32_t b) { // Q16.16 multiply return (int32_t)(((int64_t)a * b) >> 16); } static inline int32_t sat1(int32_t a) { // clamp to +-1.0 if (a > 65536) a = 65536; if (a < -65536) a = -65536; return a; } static inline int32_t sin_q(uint16_t ph) { // sine, +-32767 return g_sin[ph >> 6]; } static inline int32_t softclip(int32_t x) { // gentle limiter if (x > 20000) x = 20000 + ((x - 20000) >> 2); else if (x < -20000) x = -20000 - ((-x - 20000) >> 2); if (x > 32000) x = 32000; if (x < -32000) x = -32000; return x; } // ------------------------------- the composer ------------------------------ static void lorenz_step(void) { const int32_t SIGMA = 10 << 16, BETA = 174762, DT = 262; // dt = 0.004 s int32_t dx = mulq(SIGMA, g_y - g_x); int32_t dy = mulq(g_x, g_rho - g_z) - g_y; int32_t dz = mulq(g_x, g_y) - mulq(BETA, g_z); g_x += mulq(dx, DT); g_y += mulq(dy, DT); g_z += mulq(dz, DT); } // Pluck a string. The attractor composes: the note is drawn from its own // chaotic state, the excitation noise is seeded by it, and the note kicks // the attractor back -- melody and timbre co-evolve. static void ks_trigger(void) { voice_t *v = &g_voice[g_voice_next++ & 3]; uint32_t r = (uint32_t)g_x ^ ((uint32_t)g_y * 3u) ^ ((uint32_t)g_z * 5u) ^ (g_tick >> 6); r = (r >> 7) ^ (r << 13); uint32_t idx = (r >> 11) % 11u; uint32_t f = (uint32_t)g_pent[idx]; uint32_t len = (uint32_t)((((uint64_t)SAMPLE_RATE << 32) / (uint64_t)f) >> 16); if (len < 16) len = 16; if (len > 500) len =

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