UART TX DMA issues

[aa bb]

Posted on November 19, 2017 at 18:16

Hi,

I am trying to set up a uart TX using DMA to send data (mostly strings).

I am using FREERTOS. The semaphore is taken when I want to send the data and released when the UART_EndTransmit_IT() function is called.

The issue is that I have to add delay between data sent (~10ms).otherwise the strings sent are not complete. 

I don't understand why this is necessary..

I ma using: HAL_UART_Transmit_DMA() to send data.

Anyone witht the same problem?

Cheers,

A

[S.Ma]

Posted on November 19, 2017 at 20:47

Do you wait for the DMA transfer completion before the next string is pushed in?

A FIFO behaviour is what seems best for UART Tx, or a DMA block FIFO...

[aa bb]

Posted on November 19, 2017 at 22:18

Yes, I release the semaphore when this function is called: 

UART_EndTransmit_IT()

[S.Ma]

Posted on November 20, 2017 at 08:13

Try to activate the DMA only when the UART TX is ready to proceed (status register of UART) as extra security.

[aa bb]

Posted on November 23, 2017 at 19:02

Hi, 

Still not working, I can't figure out what's wrong. That must be a very stupid thing..

[waclawek.jan]

Posted on November 23, 2017 at 19:23

Crystal ball hazy here.

The semaphore is taken when I want to send the data and released when the UART_EndTransmit_IT() function is called.

What semaphore? Is it some code of yours inserted into Cube sources, into UART_EndTransmi_IT() function? If not, what do you exactly mean by it? What exactly is the consequence of 'semaphore taken' and 'released'?

The issue is that I have to add delay between data sent (~10ms).otherwise the strings sent are not complete. 

Where did you add the delay exactly? How exactly are the strings not complete?

JW

[aa bb]

Posted on November 23, 2017 at 19:30

Okay, here it is my sending function:

void Console_PrintFmt(const char *fmt, ...)

{

    if (fmt == NULL)

    return;

if (xSemaphoreTake(consolePrint_mutex, osWaitForever) == pdTRUE)

{

    int n;

    int size = CONSOLE__MAX_BUFFER_LENGTH - 1;

    char pBuffer[size+1];

    va_list va;

    TimerMsType timeNow = TimerMs_GetTimeMs();

    memset(pBuffer, 0, size+1);

    n = snprintf(pBuffer, size, '[%d.%03d]:', (int)timeNow / 1000, (int)timeNow % 1000);

    va_start(va,fmt);

    n += vsnprintf(pBuffer + n, size - n, fmt, va);

    va_end(va);

    if ((0 < n) && (n < size))

   {

        HAL_UART_Transmit_DMA(&huart1, (uint8_t* )pBuffer, n);

       osDelay(20);

    }

    else

    {

         xSemaphoreGive(consolePrint_mutex);

    }

  }

}

Mu mutex is released when HAL_UART_TxCpltCallback() is called. 

void HAL_UART_TxCpltCallback(UART_HandleTypeDef * huart)

{

    portBASE_TYPE higherPriorityWoken = pdFALSE;

    xSemaphoreGiveFromISR(consolePrint_mutex, NULL);

    if (higherPriorityWoken)

    {

         portYIELD_FROM_ISR(higherPriorityWoken);

     }

}

I have do add the delay just after calling 

HAL_UART_Transmit_DMA()...

Sorry but the <p> code </p> doesn't work...