fix noise

board/stm32h7/sound.h

@@ -5,23 +5,41 @@ __attribute__((section(".sram4"))) static uint16_t sound_rx_buf[2][SOUND_RX_BUF_
 
 static uint8_t sound_idle_count;
 
+void sound_tick(void) {
+  if (sound_idle_count > 0U) {
+    sound_idle_count--;
+    if (sound_idle_count == 0U) {
+      current_board->set_amp_enabled(false);
+    }
+  }
+}
+
 // Playback processing
 static void BDMA_Channel0_IRQ_Handler(void) {
   __attribute__((section(".sram4"))) static uint16_t tx_buf[SOUND_TX_BUF_SIZE];
 
   BDMA->IFCR |= BDMA_IFCR_CGIF0; // clear flag
 
-  // process samples (shift to 12b and bias to be unsigned)
-  // since we are playing mono and receiving stereo, we take every other sample
   uint8_t buf_idx = (((BDMA_Channel0->CCR & BDMA_CCR_CT) >> BDMA_CCR_CT_Pos) == 1U) ? 0U : 1U;
+
+  // process samples (shift to 12b and bias to be unsigned)
+  bool sound_playing = false;
   for (uint16_t i=0U; i < SOUND_RX_BUF_SIZE; i += 2U) {
+    // since we are playing mono and receiving stereo, we take every other sample
     tx_buf[i/2U] = ((sound_rx_buf[buf_idx][i] + (1UL << 14)) >> 3);
+    if (sound_rx_buf[buf_idx][i] > 0U) {
+      sound_playing = true;
+    }
   }
 
-  if (sound_idle_count == 0U) {
-    current_board->set_amp_enabled(true);
+  // manage amp state
+  if (sound_playing) {
+    if (sound_idle_count == 0U) {
+      current_board->set_amp_enabled(true);
+    }
+    sound_idle_count = 4U;
   }
-  sound_idle_count = 2U;
+  sound_tick();
 
   DMA1->LIFCR |= 0xF40;
   DMA1_Stream1->CR &= ~DMA_SxCR_EN;
@@ -30,15 +48,6 @@ static void BDMA_Channel0_IRQ_Handler(void) {
   DMA1_Stream1->CR |= DMA_SxCR_EN;
 }
 
-void sound_tick(void) {
-  if (sound_idle_count > 0U) {
-    sound_idle_count--;
-    if (sound_idle_count == 0U) {
-      current_board->set_amp_enabled(false);
-    }
-  }
-}
-
 void sound_init(void) {
   REGISTER_INTERRUPT(BDMA_Channel0_IRQn, BDMA_Channel0_IRQ_Handler, 64U, FAULT_INTERRUPT_RATE_SOUND_DMA)