add pio_i2s example for RP2040

examples/rp/src/bin/pio_i2s.rs

@@ -0,0 +1,130 @@
+//! This example shows generating audio and sending it to a connected i2s DAC using the PIO
+//! module of the RP2040.
+//!
+//! Connect the i2s DAC as follows:
+//!   bclk : GPIO 18
+//!   lrc  : GPIO 19
+//!   din  : GPIO 20
+//! Then hold down the boot select button to trigger a rising triangle waveform.
+
+#![no_std]
+#![no_main]
+
+use core::mem;
+
+use defmt_rtt as _;
+use embassy_executor::Spawner;
+use embassy_rp::{
+    bind_interrupts,
+    peripherals::PIO0,
+    pio::{Config, FifoJoin, InterruptHandler, Pio, ShiftConfig, ShiftDirection},
+    Peripheral,
+};
+use fixed::traits::ToFixed;
+use panic_probe as _;
+use static_cell::StaticCell;
+
+bind_interrupts!(struct Irqs {
+    PIO0_IRQ_0 => InterruptHandler<PIO0>;
+});
+
+const SAMPLE_RATE: u32 = 48_000;
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let mut p = embassy_rp::init(Default::default());
+
+    // Setup pio state machine for i2s output
+    let mut pio = Pio::new(p.PIO0, Irqs);
+
+    #[rustfmt::skip]
+    let pio_program = pio_proc::pio_asm!(
+        ".side_set 2",
+        "    set x, 14          side 0b01", // side 0bWB - W = Word Clock, B = Bit Clock
+        "left_data:",
+        "    out pins, 1        side 0b00",
+        "    jmp x-- left_data  side 0b01",
+        "    out pins 1         side 0b10",
+        "    set x, 14          side 0b11",
+        "right_data:",
+        "    out pins 1         side 0b10",
+        "    jmp x-- right_data side 0b11",
+        "    out pins 1         side 0b00",
+    );
+
+    let bit_clock_pin = p.PIN_18;
+    let left_right_clock_pin = p.PIN_19;
+    let data_pin = p.PIN_20;
+
+    let data_pin = pio.common.make_pio_pin(data_pin);
+    let bit_clock_pin = pio.common.make_pio_pin(bit_clock_pin);
+    let left_right_clock_pin = pio.common.make_pio_pin(left_right_clock_pin);
+
+    let cfg = {
+        let mut cfg = Config::default();
+        cfg.use_program(
+            &pio.common.load_program(&pio_program.program),
+            &[&bit_clock_pin, &left_right_clock_pin],
+        );
+        cfg.set_out_pins(&[&data_pin]);
+        const BIT_DEPTH: u32 = 16;
+        const CHANNELS: u32 = 2;
+        let clock_frequency = SAMPLE_RATE * BIT_DEPTH * CHANNELS;
+        cfg.clock_divider = (125_000_000. / clock_frequency as f64 / 2.).to_fixed();
+        cfg.shift_out = ShiftConfig {
+            threshold: 32,
+            direction: ShiftDirection::Left,
+            auto_fill: true,
+        };
+        // join fifos to have twice the time to start the next dma transfer
+        cfg.fifo_join = FifoJoin::TxOnly;
+        cfg
+    };
+    pio.sm0.set_config(&cfg);
+    pio.sm0.set_pin_dirs(
+        embassy_rp::pio::Direction::Out,
+        &[&data_pin, &left_right_clock_pin, &bit_clock_pin],
+    );
+
+    // create two audio buffers (back and front) which will take turns being
+    // filled with new audio data and being sent to the pio fifo using dma
+    const BUFFER_SIZE: usize = 960;
+    static DMA_BUFFER: StaticCell<[u32; BUFFER_SIZE * 2]> = StaticCell::new();
+    let dma_buffer = DMA_BUFFER.init_with(|| [0u32; BUFFER_SIZE * 2]);
+    let (mut back_buffer, mut front_buffer) = dma_buffer.split_at_mut(BUFFER_SIZE);
+
+    // start pio state machine
+    pio.sm0.set_enable(true);
+    let tx = pio.sm0.tx();
+    let mut dma_ref = p.DMA_CH0.into_ref();
+
+    let mut fade_value: i32 = 0;
+    let mut phase: i32 = 0;
+
+    loop {
+        // trigger transfer of front buffer data to the pio fifo
+        // but don't await the returned future, yet
+        let dma_future = tx.dma_push(dma_ref.reborrow(), front_buffer);
+
+        // fade in audio when bootsel is pressed
+        let fade_target = if p.BOOTSEL.is_pressed() { i32::MAX } else { 0 };
+
+        // fill back buffer with fresh audio samples before awaiting the dma future
+        for s in back_buffer.iter_mut() {
+            // exponential approach of fade_value => fade_target
+            fade_value += (fade_target - fade_value) >> 14;
+            // generate triangle wave with amplitude and frequency based on fade value
+            phase = (phase + (fade_value >> 22)) & 0xffff;
+            let triangle_sample = (phase as i16 as i32).abs() - 16384; 
+            let sample = (triangle_sample * (fade_value >> 15)) >> 16;
+            // duplicate mono sample into lower and upper half of dma word
+            *s = (sample as u16 as u32) * 0x10001;
+        }
+
+        // now await the dma future. once the dma finishes, the next buffer needs to be queued
+        // within DMA_DEPTH / SAMPLE_RATE = 8 / 48000 seconds = 166us
+        dma_future.await;
+        mem::swap(&mut back_buffer, &mut front_buffer);
+    }
+}
+