add ws2812 example for stm32f4 with PWM and DMA

examples/stm32f4/src/bin/ws2812_pwm_dma.rs

@@ -0,0 +1,135 @@
+// 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.
+//
+// This demo is a combination of HAL, PAC, and manually invoke `dma::Transfer`
+//
+// 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]
+#![feature(type_alias_impl_trait)]
+
+use embassy_executor::Spawner;
+
+use embassy_stm32::{
+    gpio::OutputType,
+    pac,
+    time::khz,
+    timer::{
+        simple_pwm::{PwmPin, SimplePwm},
+        Channel, CountingMode,
+    },
+};
+use embassy_time::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.sys = Sysclk::PLL1_P;
+        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,
+        });
+    }
+
+    let mut dp = embassy_stm32::init(device_config);
+
+    let mut ws2812_pwm = SimplePwm::new(
+        dp.TIM3,
+        Some(PwmPin::new_ch1(dp.PB4, OutputType::PushPull)),
+        None,
+        None,
+        None,
+        khz(800), // data rate of ws2812
+        CountingMode::EdgeAlignedUp,
+    );
+
+    // PAC level hacking,
+    // enable auto-reload preload, and enable timer-update-event trigger DMA
+    {
+        pac::TIM3.cr1().modify(|v| v.set_arpe(true));
+        pac::TIM3.dier().modify(|v| v.set_ude(true));
+    }
+
+    // construct ws2812 non-return-to-zero (NRZ) code bit by bit
+
+    let max_duty = ws2812_pwm.get_max_duty();
+    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];
+
+    // make sure PWM output keep low on first start
+    ws2812_pwm.set_duty(Channel::Ch1, 0);
+
+    {
+        use embassy_stm32::dma::{Burst, FifoThreshold, Transfer, TransferOptions};
+
+        // configure FIFO and MBURST of DMA, to minimize DMA occupation on AHB/APB
+        let mut dma_transfer_option = TransferOptions::default();
+        dma_transfer_option.fifo_threshold = Some(FifoThreshold::Full);
+        dma_transfer_option.mburst = Burst::Incr8;
+
+        let mut color_list_index = 0;
+
+        loop {
+            // start PWM output
+            ws2812_pwm.enable(Channel::Ch1);
+
+            unsafe {
+                Transfer::new_write(
+                    // with &mut, we can easily reuse same DMA channel multiple times
+                    &mut dp.DMA1_CH2,
+                    5,
+                    color_list[color_list_index],
+                    pac::TIM3.ccr(0).as_ptr() as *mut _,
+                    dma_transfer_option,
+                )
+                .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;
+            }
+
+            // stop PWM output for saving some energy
+            ws2812_pwm.disable(Channel::Ch1);
+
+            // wait another half second, so that we can see color change
+            Timer::after_millis(500).await;
+
+            // flip the index bit so that next round DMA transfer the other color data
+            color_list_index ^= 1;
+        }
+    }
+}