96 lines
3.8 KiB
Rust
96 lines
3.8 KiB
Rust
// Mimic PWM with SPI, to control ws2812
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// We assume the DIN pin of ws2812 connect to GPIO PB5, and ws2812 is properly powered.
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//
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// The idea is that the data rate of ws2812 is 800 kHz, and it use different duty ratio to represent bit 0 and bit 1.
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// Thus we can adjust SPI to send each *round* of data at 800 kHz, and in each *round*, we can adjust each *bit* to mimic 2 different PWM waveform.
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// such that the output waveform meet the bit representation of ws2812.
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//
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// If you want to save SPI for other purpose, you may want to take a look at `ws2812_pwm_dma.rs` file, which make use of TIM and DMA.
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//
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// Warning:
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// DO NOT stare at ws2812 directly (especially after each MCU Reset), its (max) brightness could easily make your eyes feel burn.
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#![no_std]
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#![no_main]
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use embassy_stm32::spi;
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use embassy_stm32::time::khz;
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use embassy_time::{Duration, Ticker, Timer};
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use {defmt_rtt as _, panic_probe as _};
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// we use 16 bit data frame format of SPI, to let timing as accurate as possible.
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// thanks to loose tolerance of ws2812 timing, you can also use 8 bit data frame format, thus you will need to adjust the bit representation.
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const N0: u16 = 0b1111100000000000u16; // ws2812 Bit 0 high level timing
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const N1: u16 = 0b1111111111000000u16; // ws2812 Bit 1 high level timing
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// ws2812 only need 24 bits for each LED,
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// but we add one bit more to keep SPI output low at the end
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static TURN_OFF: [u16; 25] = [
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N0, N0, N0, N0, N0, N0, N0, N0, // Green
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N0, N0, N0, N0, N0, N0, N0, N0, // Red
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N0, N0, N0, N0, N0, N0, N0, N0, // Blue
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0, // keep SPI output low after last bit
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];
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static DIM_WHITE: [u16; 25] = [
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N0, N0, N0, N0, N0, N0, N1, N0, // Green
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N0, N0, N0, N0, N0, N0, N1, N0, // Red
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N0, N0, N0, N0, N0, N0, N1, N0, // Blue
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0, // keep SPI output low after last bit
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];
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static COLOR_LIST: &[&[u16]] = &[&TURN_OFF, &DIM_WHITE];
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#[embassy_executor::main]
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async fn main(_spawner: embassy_executor::Spawner) {
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let mut device_config = embassy_stm32::Config::default();
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// Since we use 16 bit SPI, and we need each round 800 kHz,
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// thus SPI output speed should be 800 kHz * 16 = 12.8 MHz, and APB clock should be 2 * 12.8 MHz = 25.6 MHz.
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//
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// As for my setup, with 12 MHz HSE, I got 25.5 MHz SYSCLK, which is slightly slower, but it's ok for ws2812.
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{
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use embassy_stm32::rcc::{Hse, HseMode, Pll, PllMul, PllPDiv, PllPreDiv, PllSource, Sysclk};
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use embassy_stm32::time::mhz;
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device_config.enable_debug_during_sleep = true;
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device_config.rcc.hse = Some(Hse {
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freq: mhz(12),
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mode: HseMode::Oscillator,
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});
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device_config.rcc.pll_src = PllSource::HSE;
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device_config.rcc.pll = Some(Pll {
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prediv: PllPreDiv::DIV6,
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mul: PllMul::MUL102,
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divp: Some(PllPDiv::DIV8),
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divq: None,
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divr: None,
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});
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device_config.rcc.sys = Sysclk::PLL1_P;
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}
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let dp = embassy_stm32::init(device_config);
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// Set SPI output speed.
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// It's ok to blindly set frequency to 12800 kHz, the hal crate will take care of the SPI CR1 BR field.
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// And in my case, the real bit rate will be 25.5 MHz / 2 = 12_750 kHz
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let mut spi_config = spi::Config::default();
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spi_config.frequency = khz(12_800);
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// Since we only output waveform, then the Rx and Sck and RxDma it is not considered
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let mut ws2812_spi = spi::Spi::new_txonly_nosck(dp.SPI1, dp.PB5, dp.DMA2_CH3, spi_config);
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// flip color at 2 Hz
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let mut ticker = Ticker::every(Duration::from_millis(500));
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loop {
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for &color in COLOR_LIST {
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ws2812_spi.write(color).await.unwrap();
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// ws2812 need at least 50 us low level input to confirm the input data and change it's state
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Timer::after_micros(50).await;
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// wait until ticker tick
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ticker.next().await;
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}
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}
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}
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