2 files changed, 152 insertions, 36 deletions

diff --git a/examples/stm32f4/src/bin/ws2812_pwm_dma.rs b/examples/stm32f4/src/bin/ws2812_pwm_dma.rs
index 9835c07e4..cdce36f2e 100644
--- a/examples/stm32f4/src/bin/ws2812_pwm_dma.rs
+++ b/examples/stm32f4/src/bin/ws2812_pwm_dma.rs
@@ -1,7 +1,16 @@
 // 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`
+// 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 let TIM Update Event trigger a DMA transfer, then let DMA change CCR value,
+// such that pwm duty ratio meet the bit representation of ws2812.
+//
+// You may want to modify TIM CCR with Cortex core directly,
+// but according to my test, Cortex core will need to run far more than 100 MHz to catch up with TIM.
+// Thus we need to use a DMA.
+//
+// This demo is a combination of HAL, PAC, and manually invoke `dma::Transfer`.
+// If you need a simpler way to control ws2812, you may want to take a look at `ws2812_spi.rs` file, which make use of SPI.
 //
 // Warning:
 // DO NOT stare at ws2812 directy (especially after each MCU Reset), its (max) brightness could easily make your eyes feel burn.
@@ -12,10 +21,11 @@
 use embassy_executor::Spawner;
 use embassy_stm32::gpio::OutputType;
 use embassy_stm32::pac;
+use embassy_stm32::pac::timer::vals::Ocpe;
 use embassy_stm32::time::khz;
 use embassy_stm32::timer::simple_pwm::{PwmPin, SimplePwm};
 use embassy_stm32::timer::{Channel, CountingMode};
-use embassy_time::Timer;
+use embassy_time::{Duration, Ticker, Timer};
 use {defmt_rtt as _, panic_probe as _};
 
 #[embassy_executor::main]
@@ -32,7 +42,6 @@ async fn main(_spawner: Spawner) {
             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,
@@ -41,6 +50,7 @@ async fn main(_spawner: Spawner) {
             divq: None,
             divr: None,
         });
+        device_config.rcc.sys = Sysclk::PLL1_P;
     }
 
     let mut dp = embassy_stm32::init(device_config);
@@ -55,14 +65,8 @@ async fn main(_spawner: Spawner) {
         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
+    // ws2812 only need 24 bits for each LED, but we add one bit more to keep PWM output low
 
     let max_duty = ws2812_pwm.get_max_duty();
     let n0 = 8 * max_duty / 25; // ws2812 Bit 0 high level timing
@@ -82,10 +86,16 @@ async fn main(_spawner: Spawner) {
         0,  // keep PWM output low after a transfer
     ];
 
-    let color_list = [&turn_off, &dim_white];
+    let color_list = &[&turn_off, &dim_white];
 
     let pwm_channel = Channel::Ch1;
 
+    // PAC level hacking, enable output compare preload
+    // keep output waveform integrity
+    pac::TIM3
+        .ccmr_output(pwm_channel.index())
+        .modify(|v| v.set_ocpe(0, Ocpe::ENABLED));
+
     // make sure PWM output keep low on first start
     ws2812_pwm.set_duty(pwm_channel, 0);
 
@@ -97,34 +107,45 @@ async fn main(_spawner: Spawner) {
         dma_transfer_option.fifo_threshold = Some(FifoThreshold::Full);
         dma_transfer_option.mburst = Burst::Incr8;
 
-        let mut color_list_index = 0;
+        // flip color at 2 Hz
+        let mut ticker = Ticker::every(Duration::from_millis(500));
 
         loop {
-            // start PWM output
-            ws2812_pwm.enable(pwm_channel);
-
-            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(pwm_channel.index()).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;
+            for &color in color_list {
+                // start PWM output
+                ws2812_pwm.enable(pwm_channel);
+
+                // PAC level hacking, enable timer-update-event trigger DMA
+                pac::TIM3.dier().modify(|v| v.set_ude(true));
+
+                unsafe {
+                    Transfer::new_write(
+                        // with &mut, we can easily reuse same DMA channel multiple times
+                        &mut dp.DMA1_CH2,
+                        5,
+                        color,
+                        pac::TIM3.ccr(pwm_channel.index()).as_ptr() as *mut _,
+                        dma_transfer_option,
+                    )
+                    .await;
+
+                    // Turn off timer-update-event trigger DMA as soon as possible.
+                    // Then clean the FIFO Error Flag if set.
+                    pac::TIM3.dier().modify(|v| v.set_ude(false));
+                    if pac::DMA1.isr(0).read().feif(2) {
+                        pac::DMA1.ifcr(0).write(|v| v.set_feif(2, true));
+                    }
+
+                    // 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(pwm_channel);
+
+                // wait until ticker tick
+                ticker.next().await;
             }
-
-            // stop PWM output for saving some energy
-            ws2812_pwm.disable(pwm_channel);
-
-            // 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;
         }
     }
 }
diff --git a/examples/stm32f4/src/bin/ws2812_spi.rs b/examples/stm32f4/src/bin/ws2812_spi.rs
new file mode 100644
index 000000000..a280a3b77
--- /dev/null
+++ b/examples/stm32f4/src/bin/ws2812_spi.rs
@@ -0,0 +1,95 @@
+// 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 directy (especially after each MCU Reset), its (max) brightness could easily make your eyes feel burn.
+
+#![no_std]
+#![no_main]
+
+use embassy_stm32::time::khz;
+use embassy_stm32::{dma, spi};
+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, dma::NoDma, 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;
+        }
+    }
+}