WIP

kernel/src/audio.rs

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+use core::{
+    sync::atomic::{AtomicBool, Ordering},
+    time::Duration,
+};
+use embassy_rp::{
+    Peri,
+    pio::Pio,
+    pio_programs::pwm::{PioPwm, PioPwmProgram},
+    pwm::{Config, Pwm, SetDutyCycle},
+};
+use embassy_time::Timer;
+
+use crate::{Audio, Irqs};
+
+const AUDIO_BUFFER_LEN: usize = 1024;
+const _: () = assert!(AUDIO_BUFFER_LEN == abi_sys::AUDIO_BUFFER_LEN);
+pub static mut AUDIO_BUFFER: [u8; AUDIO_BUFFER_LEN] = [0; AUDIO_BUFFER_LEN];
+static mut AUDIO_BUFFER_1: [u8; AUDIO_BUFFER_LEN] = [0; AUDIO_BUFFER_LEN];
+
+pub static AUDIO_BUFFER_READY: AtomicBool = AtomicBool::new(true);
+
+pub const SAMPLE_RATE_HZ: u32 = 22_050;
+
+#[embassy_executor::task]
+pub async fn audio_handler(audio: Audio) {
+    let var_name = Pio::new(audio.pio_left, Irqs);
+    let Pio {
+        mut common, sm0, ..
+    } = var_name;
+
+    let prg = PioPwmProgram::new(&mut common);
+    let mut pwm_pio = PioPwm::new(&mut common, sm0, audio.left, &prg);
+
+    let period = Duration::from_nanos(1_000_000_000 / SAMPLE_RATE_HZ as u64);
+    pwm_pio.set_period(period);
+
+    pwm_pio.start();
+
+    let sample_interval = 1_000_000 / SAMPLE_RATE_HZ as u64; // in µs ≈ 45 µs
+
+    loop {
+        for &sample in unsafe { &AUDIO_BUFFER }.iter() {
+            let period_ns = period.as_nanos() as u32;
+            let duty_ns = period_ns * (sample as u32) / 255;
+            pwm_pio.write(Duration::from_nanos(duty_ns as u64));
+            Timer::after_micros(sample_interval).await; // sample interval = 1 / sample rate
+        }
+
+        unsafe { core::mem::swap(&mut AUDIO_BUFFER, &mut AUDIO_BUFFER_1) };
+        AUDIO_BUFFER_READY.store(true, Ordering::Release)
+    }
+}