How to Receive STM32 UART echo command using HAL libraries?

Question

I am using a STM32L Discovery board (monted device STM32L476xx), for a transmit and receive UART operation using HAL libraries. I am using a FTDI chip for serial to usb conversion as I am unable to use the Virtual Com port of the STM.

I have got the HAL_UART_Transmit function working but can not get the similar receive function to work.

My UART handle Definitions void MX_USART2_UART_Init(void) {

    huart2.Instance = USART2;
    huart2.Init.BaudRate = 9600;
    huart2.Init.WordLength = UART_WORDLENGTH_8B;   // changed from 8B
    huart2.Init.StopBits = UART_STOPBITS_1;
    huart2.Init.Parity = UART_PARITY_NONE;
    huart2.Init.Mode = UART_MODE_TX_RX;
    huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart2.Init.OverSampling = UART_OVERSAMPLING_16;
    huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
    huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
    if (HAL_UART_Init(&huart2) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }

}

I used the following for Transmit function which prints a string.

char bufftr[] = "check\n";
len = strlen(bufftr);
HAL_UART_Transmit(&huart2, (uint8_t*)bufftr, len, 100);
fflush(stdout);

But I can't get a echo working where I transmit what I receive

char test[100] ;
while (1) {

        HAL_UART_Receive(&huart2, (uint8_t *)test, 4, HAL_MAX_DELAY);

        len = sizeof(test);
        HAL_UART_Transmit(&huart2, (uint8_t *)test, len, 100);  

    }

This outputs seemingly random characters of the correct length. Please let me know how can I can I get this to work and also how to get UART transmission through the virtual COM port

Answer 1

Make Sur your GPIO Rx pin in correctly configured as Rx USART2. I suppose, FTDI cable is corretly connected between RX TX STM32 pins and your computer. -For testing your RX comm let use empty While(1) loop. -Enable UART2 interrupts on CUBEMx. -Set a breakpoint in the UART2 generated ISR. When you enter any caracter on the computer terminal, your embedded soft should stop on break point. This is a way a use to check Rx connection.