USART interrupt not working as expected [STM32 Nucleo]

Question

could someone explain why i can only receive 13 chars with USART interrupt? I use '\n' to detect the end of string.

#define BUFFER_SIZE 100

char receive_buffer[BUFFER_SIZE];
char receive_data;
int receive_index = NULL;
int data_ready_index = NULL;

void USART2_receive(void const * argument){
         for(;;){
                if(data_ready_index == 1){
                HAL_UART_Transmit_IT(&huart2, (uint8_t *)"Received data: ", strlen("Received data: "));
                HAL_Delay(50);
                HAL_UART_Transmit_IT(&huart2, (uint8_t *)receive_buffer, strlen(receive_buffer));
                memset(receive_buffer, NULL, sizeof(receive_buffer));
                HAL_Delay(50);
                HAL_UART_Transmit_IT(&huart2, (uint8_t *)"\r\n", strlen("\r\n"));
                data_ready_index = NULL;
                }
         }
     }

    void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {

        if (huart->Instance == USART2){
            if (receive_data != 13){
                receive_buffer[receive_index++]=receive_data;
            }else{
                    receive_index = NULL;
                    data_ready_index = 1;                                                               
                    // Received data ready to be processed
            }
      }
    }

    void USART2_IRQHandler(void){

      HAL_UART_IRQHandler(&huart2);
      HAL_UART_Receive_IT(&huart2, (uint8_t *) &receive_data, 1);
    }

Answer 1

I found the problem. In the void USART2_receive(void const * argument) function i increased delay from 50 to 100 and then everything works fine. As @MITURAJ mentioned this may be caused by buffer overflow.

void USART2_receive(void const * argument){
    for(;;){
        if(data_ready_index == 1){
            HAL_UART_Transmit_IT(&huart2, (uint8_t *)"Received data: ", 
            strlen("Received data: "));
            HAL_Delay(100);
            HAL_UART_Transmit_IT(&huart2, (uint8_t *)receive_buffer, 
            strlen(receive_buffer));
            HAL_Delay(100);
            HAL_UART_Transmit_IT(&huart2, (uint8_t *)"\r\n", strlen("\r\n"));
            data_ready_index = NULL;
            memset(receive_buffer, NULL, sizeof(receive_buffer));
        }
    }
}

Answer 2

Finding that you need a longer delay should tip you off that you are not waiting for the Tx to actually finish. HAL_UART_Transmit_IT uses an interrupt to send bytes out (it is non-blocking). You are basically telling it to transmit, waiting a little bit, and cramming data into the buffer again before the transmit is done!

Instead I suggest that you monitor the callback to HAL_UART_TxCpltCallback and once that happens set some flag. In your USART2_receive function, wait for the flag to be set before asking it to send things again. Remember to clear the flag before waiting for it to be set again :)