damc: fix rare glitches on usb buffers

There was a cache invalidate done in USB interrupt while the SAI interrupt was writing to usb circular buffer.
This caused memory corruption as the data not yet commited to memory was thrown away by the cache invalidate.
The fix is to not use cache management functions when not using the buffer with the DMA.

Core/Src/main.c

@@ -841,7 +841,7 @@ void MPU_Config(int enable_psram)
 
  HAL_MPU_ConfigRegion(&MPU_InitStruct);
 
- /* Configure the MPU as cacheable non executable SRAM */
+ /* Configure the MPU as cacheable non executable SRAM (write back, read/write allocate) */
  MPU_InitStruct.Enable = MPU_REGION_ENABLE;
  MPU_InitStruct.BaseAddress = 0x20000000;
  MPU_InitStruct.Size = MPU_REGION_SIZE_512MB;

damc/damc_simple_lib/AudioCApi.cpp

@@ -101,7 +101,7 @@ extern "C" void BSP_AUDIO_OUT_TransferComplete_CallBack(void) {
 	BSP_AUDIO_OUT_HalfTransfer_CallBack();
 }
 
-__attribute__((used)) CircularBuffer<uint32_t, 3> usbBuffers[3];
+__attribute__((used)) CircularBuffer<uint32_t, 3, false> usbBuffers[3];
 __attribute__((used)) int32_t diff_usb[3];
 __attribute__((used)) int32_t expected_buff[3];
 __attribute__((used)) int32_t usb_buff[3];

damc/damc_simple_lib/CircularBuffer.h

@@ -11,7 +11,7 @@
 #include <stm32f7xx.h>
 #include <string.h>
 
-template<typename T, int N> class CircularBuffer {
+template<typename T, int N, bool do_manage_cache> class CircularBuffer {
 public:
 	CircularBuffer();
 
@@ -38,12 +38,12 @@ template<typename T, int N> class CircularBuffer {
 	size_t in_read_offset;
 };
 
-template<typename T, int N> CircularBuffer<T, N>::CircularBuffer() {
+template<typename T, int N, bool do_manage_cache> CircularBuffer<T, N, do_manage_cache>::CircularBuffer() {
 	memset(buffer.data(), 0, buffer.size() * sizeof(buffer[0]));
 }
 
-template<typename T, int N>
-void CircularBuffer<T, N>::writeOutBuffer(uint32_t dma_read_offset, const T* data, size_t nframes) {
+template<typename T, int N, bool do_manage_cache>
+void CircularBuffer<T, N, do_manage_cache>::writeOutBuffer(uint32_t dma_read_offset, const T* data, size_t nframes) {
 	uint16_t start = out_write_offset;
 	uint16_t size = nframes;
 
@@ -70,12 +70,17 @@ void CircularBuffer<T, N>::writeOutBuffer(uint32_t dma_read_offset, const T* dat
 	}
 
 	assert(end < buffer.size());
-	SCB_CleanDCache_by_Addr((uint32_t*) buffer.data(), buffer.size() * sizeof(buffer[0]));
+	if(do_manage_cache) {
+		SCB_CleanDCache_by_Addr((uint32_t*) buffer.data(), buffer.size() * sizeof(buffer[0]));
+	} else {
+		__DSB();
+	}
+	assert(out_write_offset == start);
 	out_write_offset = end;
 }
 
-template<typename T, int N>
-size_t CircularBuffer<T, N>::readInBuffer(uint32_t dma_write_offset, T* data, size_t nframes) {
+template<typename T, int N, bool do_manage_cache>
+size_t CircularBuffer<T, N, do_manage_cache>::readInBuffer(uint32_t dma_write_offset, T* data, size_t nframes) {
 	uint16_t start = in_read_offset;
 
 	uint16_t end = dma_write_offset;
@@ -86,13 +91,15 @@ size_t CircularBuffer<T, N>::readInBuffer(uint32_t dma_write_offset, T* data, si
 
 	if(size > nframes) {
 		size = nframes;
-		end = (in_read_offset + size) % buffer.size();
+		end = (start + size) % buffer.size();
 	}
 	assert(end < buffer.size());
 
 	uint16_t total_size = 0;
 
-	SCB_InvalidateDCache_by_Addr((uint32_t*) buffer.data(), buffer.size() * sizeof(buffer[0]));
+	if(do_manage_cache) {
+		SCB_InvalidateDCache_by_Addr((uint32_t*) buffer.data(), buffer.size() * sizeof(buffer[0]));
+	}
 
 	if(end < start) {
 		// Copy between start and end of buffer
@@ -118,6 +125,10 @@ size_t CircularBuffer<T, N>::readInBuffer(uint32_t dma_write_offset, T* data, si
 		data[i] = fill_sample;
 	}
 
+	if(!do_manage_cache) {
+		__DSB();
+	}
+	assert(in_read_offset == start);
 	in_read_offset = end;
 
 	return size;

damc/damc_simple_lib/CodecAudio.h

@@ -30,7 +30,7 @@ class CodecAudio {
 	struct CodecFrame {
 		int16_t headphone[2];
 	};
-	CircularBuffer<CodecFrame, 2> out_buffer;
-	CircularBuffer<CodecFrame, 2> in_buffer;
+	CircularBuffer<CodecFrame, 2, true> out_buffer;
+	CircularBuffer<CodecFrame, 2, true> in_buffer;
 	CodecInit codecInit;
 };