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