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// Configure TIM3 in PWM mode, and start DMA Transfer(s) to send color data into ws2812.
// We assume the DIN pin of ws2812 connect to GPIO PB4, 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 set TIM overflow at 800 kHz, and change duty ratio of TIM to meet the bit representation of ws2812.
//
// you may also want to take a look at `ws2812_spi.rs` file, which make use of SPI instead.
//
// Warning:
// DO NOT stare at ws2812 directy (especially after each MCU Reset), its (max) brightness could easily make your eyes feel burn.
#![no_std]
#![no_main]
use embassy_executor::Spawner;
use embassy_stm32::gpio::OutputType;
use embassy_stm32::time::khz;
use embassy_stm32::timer::low_level::CountingMode;
use embassy_stm32::timer::simple_pwm::{PwmPin, SimplePwm};
use embassy_stm32::timer::Channel;
use embassy_time::{Duration, Ticker, Timer};
use {defmt_rtt as _, panic_probe as _};
#[embassy_executor::main]
async fn main(_spawner: Spawner) {
let mut device_config = embassy_stm32::Config::default();
// set SYSCLK/HCLK/PCLK2 to 20 MHz, thus each tick is 0.05 us,
// and ws2812 timings are integer multiples of 0.05 us
{
use embassy_stm32::rcc::*;
use embassy_stm32::time::*;
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::MUL80,
divp: Some(PllPDiv::DIV8),
divq: None,
divr: None,
});
device_config.rcc.sys = Sysclk::PLL1_P;
}
let mut dp = embassy_stm32::init(device_config);
let mut ws2812_pwm = SimplePwm::new(
dp.TIM3,
Some(PwmPin::new(dp.PB4, OutputType::PushPull)),
None,
None,
None,
khz(800), // data rate of ws2812
CountingMode::EdgeAlignedUp,
);
// construct ws2812 non-return-to-zero (NRZ) code bit by bit
// ws2812 only need 24 bits for each LED, but we add one bit more to keep PWM output low
let max_duty = ws2812_pwm.max_duty_cycle();
let n0 = 8 * max_duty / 25; // ws2812 Bit 0 high level timing
let n1 = 2 * n0; // ws2812 Bit 1 high level timing
let turn_off = [
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 PWM output low after a transfer
];
let dim_white = [
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 PWM output low after a transfer
];
let color_list = &[&turn_off, &dim_white];
let pwm_channel = Channel::Ch1;
// make sure PWM output keep low on first start
ws2812_pwm.channel(pwm_channel).set_duty_cycle(0);
// flip color at 2 Hz
let mut ticker = Ticker::every(Duration::from_millis(500));
loop {
for &color in color_list {
// with &mut, we can easily reuse same DMA channel multiple times
ws2812_pwm.waveform_up(dp.DMA1_CH2.reborrow(), pwm_channel, color).await;
// 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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