LEDs: Send LED signal at the end of paint

Instead of refreshing as fast as possible. Saves 2000B of RAM allocated
for the LED DMA buffer in the Lisp memory pool.

Author: lukash

src/led_driver.c

@@ -30,7 +30,6 @@
 #define TIM_PERIOD ((168000000 / 2 / WS2812_CLK_HZ) - 1)
 #define WS2812_ZERO (((uint32_t) TIM_PERIOD) * 0.3)
 #define WS2812_ONE (((uint32_t) TIM_PERIOD) * 0.7)
-#define BITBUFFER_PAD 1000
 
 typedef struct {
     uint8_t pin_nr;
@@ -90,6 +89,10 @@ static void disable_dma_stream(DMA_Stream_TypeDef *dma_stream) {
     dma_stream->CR &= ~DMA_SxCR_EN;
 }
 
+static void enable_dma_stream(DMA_Stream_TypeDef *dma_stream) {
+    dma_stream->CR |= DMA_SxCR_EN;
+}
+
 // Only DMA_Stream0 and DMA_Stream3 supported as of now.
 static void init_dma_stream(
     DMA_Stream_TypeDef *dma_stream, uint16_t *buf, uint32_t buf_len, uint32_t ccr_address
@@ -110,7 +113,7 @@ static void init_dma_stream(
     }
 
     dma_stream->CR = DMA_Channel_2 | DMA_DIR_MemoryToPeripheral | DMA_MemoryInc_Enable |
-        DMA_PeripheralDataSize_HalfWord | DMA_MemoryDataSize_HalfWord | DMA_Mode_Circular |
+        DMA_PeripheralDataSize_HalfWord | DMA_MemoryDataSize_HalfWord | DMA_Mode_Normal |
         DMA_Priority_High | DMA_MemoryBurst_Single | DMA_PeripheralBurst_Single;
 
     dma_stream->FCR = 0x00000020 | DMA_FIFOThreshold_Full;
@@ -119,8 +122,19 @@ static void init_dma_stream(
     dma_stream->NDTR = buf_len;
     dma_stream->PAR = ccr_address;
 
-    // enable the stream
-    dma_stream->CR |= DMA_SxCR_EN;
+    enable_dma_stream(dma_stream);
+}
+
+static void reset_dma_stream_transfer_complete(DMA_Stream_TypeDef *dma_stream) {
+    if (dma_stream == DMA1_Stream0) {
+        DMA1->LIFCR |= DMA_LIFCR_CTCIF0;
+    } else if (dma_stream == DMA1_Stream3) {
+        DMA1->LIFCR |= DMA_LIFCR_CTCIF3;
+    }
+}
+
+static void disable_tim4_dma(uint16_t dma_source) {
+    TIM4->DIER &= ~dma_source;
 }
 
 static void enable_tim4_dma(uint16_t dma_source) {
@@ -181,9 +195,8 @@ bool led_driver_setup(LedDriver *driver, LedPin pin, const LedStrip **led_strips
         driver->bitbuffer_length += color_order_bits(strip->color_order) * strip->length;
     }
 
-    uint32_t padding_offset = driver->bitbuffer_length;
-
-    driver->bitbuffer_length += BITBUFFER_PAD;
+    // An extra array item to set the output to 0 PWM
+    ++driver->bitbuffer_length;
     driver->bitbuffer = VESC_IF->malloc(sizeof(uint16_t) * driver->bitbuffer_length);
     driver->pin = pin;
 
@@ -198,11 +211,11 @@ bool led_driver_setup(LedDriver *driver, LedPin pin, const LedStrip **led_strips
         }
     }
 
-    for (uint32_t i = 0; i < padding_offset; ++i) {
+    for (uint32_t i = 0; i < driver->bitbuffer_length - 1; ++i) {
         driver->bitbuffer[i] = WS2812_ZERO;
     }
+    driver->bitbuffer[driver->bitbuffer_length - 1] = 0;
 
-    memset(driver->bitbuffer + padding_offset, 0, sizeof(uint16_t) * BITBUFFER_PAD);
     init_hw(pin, driver->bitbuffer, driver->bitbuffer_length);
     return true;
 }
@@ -274,6 +287,13 @@ void led_driver_paint(LedDriver *driver) {
             }
         }
     }
+
+    PinHwConfig cfg = get_pin_hw_config(driver->pin);
+    disable_tim4_dma(cfg.dma_source);
+    disable_dma_stream(cfg.dma_stream);
+    reset_dma_stream_transfer_complete(cfg.dma_stream);
+    enable_dma_stream(cfg.dma_stream);
+    enable_tim4_dma(cfg.dma_source);
 }
 
 void led_driver_destroy(LedDriver *driver) {