I2S audio from esp32-c3 is mostly noise

[thedevleon]

I'm trying to use a MAX98357A together with an ESP32-C3.

I have tried both the embassy_i2s_sound and i2s_sound samples, and while I can hear the sine wave, it is drowned in noise, with very frequent cracks and pops, and also occasionally no sound at all.

I can rule out a wiring / hardware problem, since I have no problems at all getting sound to work with arduino-audio-tools, completely noise free at 44.1kHz, and have switched between both firmwares multiple times to confirm.

To reproduce, I have setup a branch on my repo with a minimal example:
https://github.com/thedevleon/embassy-audio-on-esp/tree/broken_i2s

[thedevleon]

I have a logic analyzer and an oscilloscope, so I could also look at some signals if that helps.

[bjoernQ]

I notice the crackling sound with the embassy example, too. Pretty sure it wasn't always like that 🤔
But I get a perfect sine tone with the non-embassy example - even in debug mode

[bjoernQ]

Mind trying this example?

//! This shows how to transmit data continuously via I2S
//!
//! Pins used
//! MCLK    GPIO4
//! BCLK    GPIO1
//! WS      GPIO2
//! DOUT    GPIO3
//!
//! Without an additional I2S sink device you can inspect the MCLK, BCLK, WS and
//! DOUT with a logic analyzer
//!
//! You can also connect e.g. a PCM510x to hear an annoying loud sine tone (full
//! scale), so turn down the volume before running this example.
//!
//! Wiring is like this
//!
//! | Pin   | Connected to    |
//! |-------|-----------------|
//! | BCK   | GPIO1           |
//! | DIN   | GPIO3           |
//! | LRCK  | GPIO2           |
//! | SCK   | Gnd             |
//! | GND   | Gnd             |
//! | VIN   | +3V3            |
//! | FLT   | Gnd             |
//! | FMT   | Gnd             |
//! | DEMP  | Gnd             |
//! | XSMT  | +3V3            |

#![no_std]
#![no_main]
#![feature(type_alias_impl_trait)]

use embassy_executor::Spawner;
use esp32c3_hal::{
    clock::ClockControl,
    dma::{Dma, DmaPriority},
    dma_buffers,
    embassy,
    i2s::{asynch::*, DataFormat, I2s, Standard},
    peripherals::Peripherals,
    prelude::*,
    IO,
};
use esp_backtrace as _;
use esp_hal::dma::DmaDescriptor;
use esp_println::println;

const SINE: [i16; 64] = [
    0, 3211, 6392, 9511, 12539, 15446, 18204, 20787, 23169, 25329, 27244, 28897, 30272, 31356,
    32137, 32609, 32767, 32609, 32137, 31356, 30272, 28897, 27244, 25329, 23169, 20787, 18204,
    15446, 12539, 9511, 6392, 3211, 0, -3211, -6392, -9511, -12539, -15446, -18204, -20787, -23169,
    -25329, -27244, -28897, -30272, -31356, -32137, -32609, -32767, -32609, -32137, -31356, -30272,
    -28897, -27244, -25329, -23169, -20787, -18204, -15446, -12539, -9511, -6392, -3211,
];

#[main]
async fn main(_spawner: Spawner) {
    #[cfg(feature = "log")]
    esp_println::logger::init_logger_from_env();
    println!("Init!");
    let peripherals = Peripherals::take();
    let system = peripherals.SYSTEM.split();
    let clocks = ClockControl::boot_defaults(system.clock_control).freeze();

    #[cfg(feature = "embassy-time-systick")]
    embassy::init(
        &clocks,
        esp32c3_hal::systimer::SystemTimer::new(peripherals.SYSTIMER),
    );

    #[cfg(feature = "embassy-time-timg0")]
    embassy::init(
        &clocks,
        esp32c3_hal::timer::TimerGroup::new(peripherals.TIMG0, &clocks),
    );

    let io = IO::new(peripherals.GPIO, peripherals.IO_MUX);

    let dma = Dma::new(peripherals.DMA);
    let dma_channel = dma.channel0;

    let mut tx_descriptors = [DmaDescriptor::EMPTY; 20];
    let mut rx_descriptors = [DmaDescriptor::EMPTY; 8];

    let i2s = I2s::new(
        peripherals.I2S0,
        Standard::Philips,
        DataFormat::Data16Channel16,
        44100u32.Hz(),
        dma_channel.configure(
            false,
            &mut tx_descriptors,
            &mut rx_descriptors,
            DmaPriority::Priority0,
        ),
        &clocks,
    )
    .with_mclk(io.pins.gpio4);

    let i2s_tx = i2s
        .i2s_tx
        .with_bclk(io.pins.gpio1)
        .with_ws(io.pins.gpio2)
        .with_dout(io.pins.gpio3)
        .build();

    let data =
        unsafe { core::slice::from_raw_parts(&SINE as *const _ as *const u8, SINE.len() * 2) };

    let buffer = dma_buffer();
    let mut idx = 0;
    for i in 0..usize::min(data.len(), buffer.len()) {
        buffer[i] = data[idx];

        idx += 1;

        if idx >= data.len() {
            idx = 0;
        }
    }

    let mut filler = [0u8; 10000];
    let mut idx = 32000 % data.len();

    println!("Start");
    let mut transaction = i2s_tx.write_dma_circular_async(buffer).unwrap();
    loop {
        for i in 0..filler.len() {
            filler[i] = data[(idx + i) % data.len()];
        }
        println!("Next");

        let written = transaction.push(&filler).await.unwrap();
        idx = (idx + written) % data.len();
        println!("written {}", written);
    }
}

fn dma_buffer() -> &'static mut [u8; 32000] {
    static mut BUFFER: [u8; 32000] = [0u8; 32000];
    unsafe { &mut BUFFER }
}

It's basically the same just the way DMA is setup is changed back to how it was before

[bjoernQ]

I guess I know what the problem is ... if the above example works for you, I probably have a real fix for it

[thedevleon]

I tried running your example, but I cannot find the DmaDescriptor type in esp32c3-hal 0.15.0, I guess I will need master to run your sample?

[bjoernQ]

Ah sorry for that - yes, it's not in the 0.15 release yet. If you could try it that'd awesome - if that's too cumbersome I can change it for 0.15

[thedevleon]

Can confirm, in the context of master and with your changes to the embassy sample I now get a smooth sine with no noise. Nice!

I also do get the following warning though:

warning: mutable reference of mutable static is discouraged
   --> examples/embassy_i2s_sound.rs:142:14
    |
142 |     unsafe { &mut BUFFER }
    |              ^^^^^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
    = note: reference of mutable static is a hard error from 2024 edition
    = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
    = note: `#[warn(static_mut_ref)]` on by default
help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |
142 |     unsafe { addr_of_mut!(BUFFER) }
    |              ~~~~~~~~~~~~~~~~~~~~