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embassy-rp: Make bit-depth of I2S PIO program configurable #4193

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embassy-rp: Make bit-depth of I2S PIO program configurable #4193

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edcbfeb
Make bit-depth of I2S PIO program configurable
embediver May 13, 2025
fd9ed39
Fix example
embediver May 13, 2025
5838346
Fix example for rp235x
embediver May 13, 2025
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18 changes: 13 additions & 5 deletions embassy-rp/src/pio_programs/i2s.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,10 @@ use crate::pio::{
use crate::Peri;

/// This struct represents an i2s output driver program
///
/// The sample bit-depth is set through scratch register `Y`.
/// `Y` has to be set to sample bit-depth - 2.
/// (14 = 16bit, 22 = 24bit, 30 = 32bit)
pub struct PioI2sOutProgram<'d, PIO: Instance> {
prg: LoadedProgram<'d, PIO>,
}
Expand All @@ -17,13 +21,13 @@ impl<'d, PIO: Instance> PioI2sOutProgram<'d, PIO> {
/// Load the program into the given pio
pub fn new(common: &mut Common<'d, PIO>) -> Self {
let prg = pio::pio_asm!(
".side_set 2",
" set x, 14 side 0b01", // side 0bWB - W = Word Clock, B = Bit Clock
".side_set 2", // side 0bWB - W = Word Clock, B = Bit Clock
" mov x, y side 0b01", // y stores sample depth - 2 (14 = 16bit, 22 = 24bit, 30 = 32bit)
"left_data:",
" out pins, 1 side 0b00",
" jmp x-- left_data side 0b01",
" out pins 1 side 0b10",
" set x, 14 side 0b11",
" mov x, y side 0b11",
"right_data:",
" out pins 1 side 0b10",
" jmp x-- right_data side 0b11",
Expand Down Expand Up @@ -53,7 +57,6 @@ impl<'d, P: Instance, const S: usize> PioI2sOut<'d, P, S> {
lr_clock_pin: Peri<'d, impl PioPin>,
sample_rate: u32,
bit_depth: u32,
channels: u32,
program: &PioI2sOutProgram<'d, P>,
) -> Self {
let data_pin = common.make_pio_pin(data_pin);
Expand All @@ -64,7 +67,7 @@ impl<'d, P: Instance, const S: usize> PioI2sOut<'d, P, S> {
let mut cfg = Config::default();
cfg.use_program(&program.prg, &[&bit_clock_pin, &left_right_clock_pin]);
cfg.set_out_pins(&[&data_pin]);
let clock_frequency = sample_rate * bit_depth * channels;
let clock_frequency = sample_rate * bit_depth * 2;
cfg.clock_divider = (crate::clocks::clk_sys_freq() as f64 / clock_frequency as f64 / 2.).to_fixed();
cfg.shift_out = ShiftConfig {
threshold: 32,
Expand All @@ -78,6 +81,11 @@ impl<'d, P: Instance, const S: usize> PioI2sOut<'d, P, S> {
sm.set_config(&cfg);
sm.set_pin_dirs(Direction::Out, &[&data_pin, &left_right_clock_pin, &bit_clock_pin]);

// Set the `y` register up to configure the sample depth
// The SM counts down to 0 and uses one clock cycle to set up the counter,
// which results in bit_depth - 2 as register value.
unsafe { sm.set_y(bit_depth - 2) };

sm.set_enable(true);

Self { dma: dma.into(), sm }
Expand Down
2 changes: 0 additions & 2 deletions examples/rp/src/bin/pio_i2s.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,6 @@ bind_interrupts!(struct Irqs {

const SAMPLE_RATE: u32 = 48_000;
const BIT_DEPTH: u32 = 16;
const CHANNELS: u32 = 2;

#[embassy_executor::main]
async fn main(_spawner: Spawner) {
Expand All @@ -50,7 +49,6 @@ async fn main(_spawner: Spawner) {
left_right_clock_pin,
SAMPLE_RATE,
BIT_DEPTH,
CHANNELS,
&program,
);

Expand Down
2 changes: 0 additions & 2 deletions examples/rp235x/src/bin/pio_i2s.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,6 @@ bind_interrupts!(struct Irqs {

const SAMPLE_RATE: u32 = 48_000;
const BIT_DEPTH: u32 = 16;
const CHANNELS: u32 = 2;

#[embassy_executor::main]
async fn main(_spawner: Spawner) {
Expand All @@ -50,7 +49,6 @@ async fn main(_spawner: Spawner) {
left_right_clock_pin,
SAMPLE_RATE,
BIT_DEPTH,
CHANNELS,
&program,
);

Expand Down