Posted on June 01, 2018 at 15:36using a circular RxDMA buffer
initialize before while(1)
U1RxBufferPtrOUT = 0;
HAL_UART_Receive_DMA(&huart1, (uint8_t *)Usart1RxDMABuffer, U1RxBufSize);
you can Peek at the buffer level ;
U1RxBufferPtrIN this is pointing to the next Rx byte position.
char readableU1(void) { // returns length in DMA not read.
U1RxBufferPtrIN = U1RxBufSize - huart1.hdmarx->Instance->CNDTR;
return U1RxBufferPtrIN - U1RxBufferPtrOUT;
}
if you want to read some bytes you use U1RxBufferPtrOUT. As you read bytes from the buffer, you must increment your U1RxBufferPtrOUT and wrap it at the DMA circular buffer length.
ie
The correct method to check the current receive buffer length is
RxLength = readableU1() // reads zero after initialization
just after initialization;
if you receive 10 bytes
U1RxBufferPtrIN = 10
and since U1RxBufferPtrOUT is still zero. : RxLength becomes 10.
You can poll this value readableU1() for your required packet size without reading a byte.
as you read each byte from that packet, you increment U1RxBufferPtrOUT and wrap at U1RxBufSize
char readU1(void) {
char readByte = Usart1RxDMABuffer[U1RxBufferPtrOUT++];
if (U1RxBufferPtrOUT >= U1RxBufSize) U1RxBufferPtrOUT = 0;
return readByte;
}
