This also my experience of HAL_UARTEx_RxEventCallback. It always sends in a value of 1…Size (ie, if Size of buffer is 256 bytes, then the values are 1…256, never sends in a size value of 0).
This is ok since my callback is a single line:
int tail, head;
uint8_t rxBuf[256];
void HAL_UARTEx_RxEventCallback(UART_HandleTypeDef *huart, uint16_t size)
{
tail = size % sizeof(rxBuf);
}
I call HAL_UARTEx_ReceiveToIdle_DMA once at startup and it runs all of the time. The Uart RX DMA channel is configured as CIRCULAR.
Outside of the callback, in my main code loop, I maintain a “head�? index. If head != tail, then I know there is something in the receive DMA buffer. I extract and parse the bytes one-by-one, advancing head:
HAL_UARTEx_ReceiveToIdle_DMA(&huart2, rxBuf, sizeof(rxBuf));
while (head != tail)
{
ParseByte(rxBuf[head]);
head = (head + 1) % sizeof(rxBuf);
}
This method is very simple and works very well, no issues, as long as the main code loop can extract and process the bytes fast enough before the DMA receive buffer fills up. In my case, this never happens because the receive buffer is large enough and the incoming messages are relatively short and simple.
Note: I am communicating over an RS-485 bus, master-slave configuration.
Note: I do not use the STM32's Uart DE peripheral signals for turning on the RS–485 transceiver when responding to the master. Instead, I use an arbitrary GPIO so that I can free up those DE pins for other functions. I turn on the GPIO before calling the DMA transmit function. In the transmit complete callback, I turn off the GPIO. This works perfectly.
Running on an STM32L47x.
Open to hearing feedback on this method.
