Problem Description
I am having some trouble using HAL_UART_Receive_IT() to receive UART data in interrupt mode, the callback HAL_UART_RxCpltCallback() only triggers once for the first byte, subsequent bytes do not trigger the interrupt. I don't know if there is some problem with my implementation or if the problem is in STM32CubeH5 (v1.5.0). I would really appreciate some help!
Symptoms
HAL_UART_RxCpltCallback() executes correctly for the first received byte.
Calling HAL_UART_Receive_IT() again does not fix the issue.
No further interrupts are generated, even though UART data is arriving.
Root Cause?
I did some digging and found the UART interrupt handler (UART_RxISR_8BIT) clears the RxISR function pointer (huart->RxISR = NULL) after processing the first byte. This prevents the interrupt from being handled correctly again, even if HAL_UART_Receive_IT() is called again.
Workaround: Manually Restore huart->RxISR
To workaround this, I added one line to manually reassign huart->RxISR in the HAL_UART_RxCpltCallback(), when I do this I get the expected behavior:
uint8_t rx_byte; // Single-byte buffer for interrupt mode
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {
if (huart == &huart2) {
// Process the received byte (e.g., store or print)
printf("Received: %c\n", rx_byte);
// FIX: Restore the RxISR function pointer
huart->RxISR = UART_RxISR_8BIT; // Use UART_RxISR_16BIT for 16-bit mode
// Restart interrupt-based receive
HAL_UART_Receive_IT(huart, &rx_byte, 1);
}
}
int main() {
HAL_Init();
SystemClock_Config();
MX_USART2_UART_Init();
// Start the first interrupt-based receive
HAL_UART_Receive_IT(&huart2, &rx_byte, 1);
while (1) {
// Main loop does other tasks
}
}
