Serial port library read function and Free RTOS

[Andreas48752]

Hi! 

I am trying to use serial port library with Free RTOS (SDK 15.3). I created a read task but when I try to read, the function does sometimes receive wrong bytes. I also get "NRF_SERIAL_EVENT_DRV_ERR" events when adding an event handler. Does anybode know why?

Following my code:

static void sleep_handler(void)
{
    __WFE();
    __SEV();
    __WFE();
}

NRF_SERIAL_DRV_UART_CONFIG_DEF(m_uarte0_drv_config,
                      RX_PIN_NUMBER, ARDUINO_SCL_PIN,
                      RTS_PIN_NUMBER, CTS_PIN_NUMBER,
                      NRF_UART_HWFC_DISABLED, NRF_UART_PARITY_EXCLUDED,
                      NRF_UART_BAUDRATE_115200,
                      UART_DEFAULT_CONFIG_IRQ_PRIORITY);

NRF_SERIAL_DRV_UART_CONFIG_DEF(m_uarte1_drv_config,
                      ARDUINO_SDA_PIN, TX_PIN_NUMBER,
                      RTS_PIN_NUMBER, CTS_PIN_NUMBER,
                      NRF_UART_HWFC_DISABLED, NRF_UART_PARITY_EXCLUDED,
                      NRF_UART_BAUDRATE_115200,
                      UART_DEFAULT_CONFIG_IRQ_PRIORITY);


#define SERIAL_FIFO_TX_SIZE 32
#define SERIAL_FIFO_RX_SIZE 32

NRF_SERIAL_QUEUES_DEF(serial0_queues, SERIAL_FIFO_TX_SIZE, SERIAL_FIFO_RX_SIZE);
NRF_SERIAL_QUEUES_DEF(serial1_queues, SERIAL_FIFO_TX_SIZE, SERIAL_FIFO_RX_SIZE);


#define SERIAL_BUFF_TX_SIZE 1
#define SERIAL_BUFF_RX_SIZE 1

NRF_SERIAL_BUFFERS_DEF(serial0_buffs, SERIAL_BUFF_TX_SIZE, SERIAL_BUFF_RX_SIZE);
NRF_SERIAL_BUFFERS_DEF(serial1_buffs, SERIAL_BUFF_TX_SIZE, SERIAL_BUFF_RX_SIZE);


NRF_SERIAL_CONFIG_DEF(serial0_config, NRF_SERIAL_MODE_DMA,
                      &serial0_queues, &serial0_buffs, NULL, sleep_handler);
NRF_SERIAL_CONFIG_DEF(serial1_config, NRF_SERIAL_MODE_DMA,
                      &serial1_queues, &serial1_buffs, NULL, sleep_handler);


NRF_SERIAL_UART_DEF(serial0_uarte, 0);
NRF_SERIAL_UART_DEF(serial1_uarte, 1);

void UART_Read_Task()
{
   char c;
   ret_code_t ret;
   while(true)
   {
      ret = nrf_serial_read(&serial0_uarte, &c, sizeof(c), NULL, 0);
      if (ret == NRF_SUCCESS)
      {
          // todo
      }

      ret = nrf_serial_read(&serial1_uarte, &c, 1, NULL, 0);
      if (ret == NRF_SUCCESS)
      {
         // todo
      }
  }
}

int main(void)
{
    ret_code_t ret;

    ret = nrf_drv_clock_init();
    APP_ERROR_CHECK(ret);
    ret = nrf_drv_power_init(NULL);
    APP_ERROR_CHECK(ret);

    nrf_drv_clock_lfclk_request(NULL);
    ret = app_timer_init();

    timers_init();


    APP_ERROR_CHECK(ret);
    log_init();
    // Initialize LEDs and buttons.
    bsp_board_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS);

    ret = nrf_serial_init(&serial0_uarte, &m_uarte0_drv_config, &serial0_config);
    APP_ERROR_CHECK(ret);

    ret = nrf_serial_init(&serial1_uarte, &m_uarte1_drv_config, &serial1_config);
    APP_ERROR_CHECK(ret);

    // other stuff here
    
     if (pdPASS != xTaskCreate(UART_Read_Task,
                              "UART_Read",
                              USBD_STACK_SIZE,
                              NULL,
                              1,
                              &m_UART_Read_thread))
    {
        APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
    }

      // Activate deep sleep mode.
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
    // Start FreeRTOS scheduler.
    vTaskStartScheduler();


    for (;;)
    {
       APP_ERROR_HANDLER(NRF_ERROR_FORBIDDEN);
    }
    
}

[Susheel Nuguru]

Can you show us the actual values of UART_DEFAULT_CONFIG_IRQ_PRIORITY, the read task priority and the code snippet on exactly when you start the 50ms timeout timer? 

[Andreas48752]

Hi Susheel,

#define UART_DEFAULT_CONFIG_IRQ_PRIORITY 6

The read task priority is 1 (xTaskCreate in above code for UART_Read).

the 50 ms timeout is the last parameter of "nrf_serial_read" (also in above code).

[Susheel Nuguru]

The problem could be the mode which you seem to have configured to be DMA mode to work in blocking mode at the time of initialization.

I am not sure if this combo works fine with the mutex, queues used from nRF5 SDK combined with FreeRTOS. 

Does your read had to be blocking? I would recommend you to use non blocking reads or make the driver work in interrupt mode

Do not forget if you use interrupt mode

Warning
Do not use synchronous API (timeout_ms parameter > 0) in IRQ context. It may lead to a deadlock because the timeout interrupt cannot preempt the current IRQ context.

[Andreas48752]

Thanks for the reply.

As far as I know the second UART must be configured to use DMA (because it's a UARTE). How do I use none blocking reads?  

[Susheel Nuguru]

Andreas48752 said:

How do I use none blocking reads?  

 setting timeout_ms to 0 is what makes it work in non-blocking mode.