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//! This example shows generating audio and sending it to a connected i2s DAC using the PIO
//! module of the RP235x.
//!
//! 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 embassy_executor::Spawner;
use embassy_rp::bind_interrupts;
use embassy_rp::gpio::{Input, Pull};
use embassy_rp::peripherals::PIO0;
use embassy_rp::pio::{InterruptHandler, Pio};
use embassy_rp::pio_programs::i2s::{PioI2sOut, PioI2sOutProgram};
use static_cell::StaticCell;
use {defmt_rtt as _, panic_probe as _};
bind_interrupts!(struct Irqs {
PIO0_IRQ_0 => InterruptHandler<PIO0>;
});
const SAMPLE_RATE: u32 = 48_000;
const BIT_DEPTH: u32 = 16;
#[embassy_executor::main]
async fn main(_spawner: Spawner) {
let p = embassy_rp::init(Default::default());
// Setup pio state machine for i2s output
let Pio { mut common, sm0, .. } = Pio::new(p.PIO0, Irqs);
let bit_clock_pin = p.PIN_18;
let left_right_clock_pin = p.PIN_19;
let data_pin = p.PIN_20;
let program = PioI2sOutProgram::new(&mut common);
let mut i2s = PioI2sOut::new(
&mut common,
sm0,
p.DMA_CH0,
data_pin,
bit_clock_pin,
left_right_clock_pin,
SAMPLE_RATE,
BIT_DEPTH,
&program,
);
let fade_input = Input::new(p.PIN_0, Pull::Up);
// 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
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 = i2s.write(front_buffer);
// fade in audio when bootsel is pressed
let fade_target = if fade_input.is_low() { 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);
}
}
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