Bare-metal, no_std no-alloc esp32 ws2812 driver for driving NeoPixel strips

esp32_ws2812_driver.rs

//! Usage:
//! let peripherals = esp_hal::init(esp_hal::Config::default().with_cpu_clock(CpuClock::max()));
//! let neopixels = ws2812_rmt::Ws2812::<'d>::new(peripherals.RMT, peripherals.GPIO3);

use esp_hal::{
    Blocking, gpio::{Level, OutputPin}, peripherals::RMT, rmt::{self, Channel, PulseCode, Tx, TxChannelConfig, TxChannelCreator}, time::Rate
};

pub struct Ws2812<'d> {
    channel: Option<Channel<'d, Blocking, Tx>>,
}

impl<'d> Ws2812<'d> {
    pub fn new(
        rmt_peripheral: RMT<'d>,
        pin: impl OutputPin + 'd,
    ) -> Self {
        let rmt = rmt::Rmt::new(rmt_peripheral, Rate::from_mhz(80)).unwrap();

        // Configure channel 0 for TX
        let tx_config = TxChannelConfig::default().with_clk_divider(1);

        let channel = Some(rmt.channel0.configure_tx(pin, tx_config).unwrap());

        Self { channel }
    }

    pub fn write(&mut self, pixels: &[[u8; 3]]) {
        let channel = self.channel.take().unwrap();

        // Worst case: 64 LEDs → 64*24 = 1536 symbols
        // That fits in C3 RMT RAM.
        let mut symbols: [PulseCode; 1536 + 2] =
            [PulseCode::default(); 1538];

        let mut idx = 0;

        for pixel in pixels {
            let bytes = [pixel[1], pixel[0], pixel[2]];

            for byte in bytes {
                for bit in (0..8).rev() {
                    let is_one = (byte >> bit) & 1 != 0;

                    symbols[idx] = if is_one {
                        ws2812_one()
                    } else {
                        ws2812_zero()
                    };

                    idx += 1;
                }
            }
        }

        // Reset pulse (>50µs low)
        symbols[idx] = PulseCode::new(Level::Low, 4000, Level::Low, 0);
        idx += 1;

        symbols[idx] = PulseCode::end_marker();

        let tx = channel.transmit(&symbols[..=idx]).unwrap();
        self.channel = Some(tx.wait().unwrap());
    }
}

fn ws2812_zero() -> PulseCode {
    PulseCode::new(Level::High, 32, Level::Low, 68)
}

fn ws2812_one() -> PulseCode {
    PulseCode::new(Level::High, 64, Level::Low, 36)
}