Call to app_uart_put() not putting anything on the TX Line

[Sami]

Hello,

I've been trying to get my call to app_uart_put() to actually place bytes on the TX pin. Interestingly enough, my call to app_uart_get() works fine and is able to receive all the commands on the RX pin. I am using SDK v17.0.2. 

My code that initializes the UART is fairly boilerplate:

   if (!uart_instance_activated)
    {
        uart_instance_activated = true;
        uint32_t err_code = NRF_SUCCESS;
        const app_uart_comm_params_t comm_params =
        {
            UART_RX_PIN,
            UART_TX_PIN,
            UART_RTS_PIN_NUMBER,
            UART_CTS_PIN_NUMBER,
            UART_HWFC,
            false,
            NRF_UART_BAUDRATE_115200
        };

        APP_UART_FIFO_INIT(&comm_params,
                       UART_RX_BUF_SIZE,
                       UART_TX_BUF_SIZE,
                      uart_error_handle,
                APP_IRQ_PRIORITY_LOWEST,
                              err_code);

        APP_ERROR_CHECK(err_code); 
    }

My code that calls app_uart_put()

uint8_t transportSend( const uint16_t bufferSize, uint8_t *pBuffer )
{
    if ( pBuffer == NULL )
    {
        NRF_LOG_INFO("NULL?");
        return TRANSPORT_ERROR;
    }

    uint32_t status = NRF_SUCCESS;

    while (app_uart_put(START_BYTE) != NRF_SUCCESS);
    nrf_delay_ms(10);

    for ( uint16_t i = 0; i < bufferSize; i++ )
    {
        //NRF_LOG_INFO("pBuffer[%d] = %d", i, pBuffer[i]);
        // UART is spaming 0xFF so it has to be escaped
        if ( ( pBuffer[i] == START_BYTE ) ||
             ( pBuffer[i] == STOP_BYTE ) ||
             ( pBuffer[i] == ESCAPE_BYTE ) ||
             ( pBuffer[i] == 0xFF ) )
        {
            //status = app_uart_put( ESCAPE_BYTE );
            while (app_uart_put(ESCAPE_BYTE) != NRF_SUCCESS);
            nrf_delay_ms(10);

            while (app_uart_put(escapeByte( pBuffer[i] )) != NRF_SUCCESS);
            nrf_delay_ms(10);
        }
        else
        {
            while (app_uart_put(pBuffer[i]) != NRF_SUCCESS);
            nrf_delay_ms(10);
        }
    } // end of for-loop

    while (app_uart_put(STOP_BYTE) != NRF_SUCCESS);
    nrf_delay_ms(10);
  
    return TRANSPORT_SUCCESS;
}

and Like I said, my code that calls app_uart_get() works just fine:

static int cala_getChar()
{
    uint8_t input = 0;
    app_uart_get(&input);
    return input;
}

Is app_uart_put() not being called correctly? Doubled checked sdk_config.h and NRFX_UART_ENABLED is 1

[Simonr]

Hi

Have you checked out the UART example projects in the SDK to see how they initialize and utilize the app_uart_put() function? Also, what pin have you set the UART TX pin as in your application?

Best regards,

Simon

[Sami]

Hi Simon,

Changing to PORT_0 pins didn't work, unfortunately. 

Are there certain flags that need to be turned on in sdk_config.h?

For instance, I noticed that 

// RETARGET_ENABLED  - retarget - Retargeting stdio functions
#ifndef RETARGET_ENABLED
#define RETARGET_ENABLED 1
#endif


I added this into my code, but still not seeing anything on the TX line. Also, 

My code has

#ifndef APP_UART_DRIVER_INSTANCE
#define APP_UART_DRIVER_INSTANCE 1
#endif


Does this need to be 0?


What about:

#ifndef NRFX_UARTE_ENABLED
#define NRFX_UARTE_ENABLED 1
#endif
//  NRFX_UARTE0_ENABLED - Enable UARTE0 instance 
#ifndef NRFX_UARTE0_ENABLED
#define NRFX_UARTE0_ENABLED 0
#endif

//  NRFX_UARTE1_ENABLED - Enable UARTE1 instance 
#ifndef NRFX_UARTE1_ENABLED
#define NRFX_UARTE1_ENABLED 0
#endif

?



Not sure why RX line works fine, but TX produces 0 output. Do I need to configure TX pull sense a certain way?

[Simonr]

What pin exactly did you move the TX pin to now? And you still don't see any error codes in your program? Since the RX pin works as intended I would think the peripheral is set up correctly, but the NRFX_UARTE_ENABLED should also set one of the instances (UARTE0 and UARTE1) to 1. Depending on what instance you use in the UART init.

Best regards,

Simon

[Sami]

I had found the problem:

Before creating an instance of UART, I attempt to gracefully tear down my CLI over UART via:

nrf_cli_stop(&m_cli_uart); // this succeeds

and then

nrf_cli_uninit(&m_cli_uart); // this hangs on NRF_ERROR_BUSY

due to

    if (cli_flag_processing_is_set(p_cli))
    {
        return NRF_ERROR_BUSY;
    }

It looks like the SDK never clears the internal flag p_cli. I was able to get around this problem by commenting out flag check.
Is there a work-around for properly clearing p_cli? 

If I comment cli_flag_processing_is_set() flag check, my UART works great!

[Simonr]

Does the nrf_cli_uninit() function just hang "forever"? I think implementing a delay or wait function until UART TX/RX transmissions are completed should let the CLI uninit successfully.

Very glad you got it working as intended though, and I don't see any issues with how you resolved it.

Best regards,

Simon

[Sami]

Yes, unfortunately, nrf_cli_uninit() will not clear the flag. I've tried looping on the call and nrf_cli_uninit() will always return NRF_ERROR_BUSY. Implementing a delay did not fix the problem. Looks like some other folks on the DevZone have experienced this as well. 

https://devzone.nordicsemi.com/f/nordic-q-a/80440/cli-stopping-and-uninitializing-error-nrf_error_busy

I'd prefer to not modify the SDK -- but if necessary, I will.

[Simonr]

As my colleague Terje suggests. Could it be that you have uninitialized the UART before calling the nrf_cli_uninit() function which causes the CLI to hang and be "busy"?

Best regards,

Simon