[NRF52840] Correct FreeRTOS logging using NRF_LOG module

Question

NRF52840 Dev Kit

NRF SDK 17.1.0

SD version 7.2

Using GCC Make to build

Using RTT logging backend

Hello all,

Currently, we are trying to migrate over to using FreeRTOS for our applicaiton, and I began by using the FreeRTOS example ble_app_hrs_freertos in the ble_peripheral directory. I've been able to get a custom service working fine, but I've been struggling with the NRF_LOG module quite a bit. Currently, I have the logging working fine as long as I am not putting any log outputs in the timer handlers, but as soon as I do that, I get one of two issues.

With NRF_LOG_DEFERRED set to 1, it appears that the application is running as the LED's are blinking and I can connect to the device via NRF Connect, but there are no log messages in the terminal past the initial "Fast advertising" found in the on_adv_evt() function. Anything beyond this, such as "Connected", "Disconnected" or any other messages I've put in are never displayed.

With NRF_LOG_DEFERRED set to 0, it works (i.e. showing all the logs) until I put a message into a timer handler. When I do that, a hard fault like the following occurs

<error> hardfault: HARD FAULT at 0x0002C19A

<error> hardfault:   R0:  0x09498C20  R1:  0x0000071F  R2:  0x0000071F  R3:  0x200072D8

<error> hardfault:   R12: 0x00000000  LR:  0x0002C18D  PSR: 0x8100000E

<error> hardfault: Cause: Data bus error (PC value stacked for tult).

I received this data using the JLinkRTTViewer program.

For quick reference, here is all of the logging related code and main form the example:

/**@brief Function for initializing the nrf log module.
 */
static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


#if NRF_LOG_ENABLED
/**@brief Thread for handling the logger.
 *
 * @details This thread is responsible for processing log entries if logs are deferred.
 *          Thread flushes all log entries and suspends. It is resumed by idle task hook.
 *
 * @param[in]   arg   Pointer used for passing some arbitrary information (context) from the
 *                    osThreadCreate() call to the thread.
 */
static void logger_thread(void * arg)
{
    UNUSED_PARAMETER(arg);

    while (1)
    {
        NRF_LOG_FLUSH();

        vTaskSuspend(NULL); // Suspend myself
    }
}
#endif //NRF_LOG_ENABLED

#if NRF_LOG_ENABLED && NRF_LOG_DEFERRED
 void log_pending_hook( void )
 {
     BaseType_t result = pdFAIL;

    if ( __get_IPSR() != 0 )
    {
        BaseType_t higherPriorityTaskWoken = pdFALSE;
        result = xTaskNotifyFromISR( m_logger_thread, 0, eSetValueWithoutOverwrite, &higherPriorityTaskWoken );

        if ( pdFAIL != result )
        {
        portYIELD_FROM_ISR( higherPriorityTaskWoken );
        }
    }
    else
    {
        UNUSED_RETURN_VALUE(xTaskNotify( m_logger_thread, 0, eSetValueWithoutOverwrite ));
    }
 }
#endif

/**@brief Function for initializing the clock.
 */
static void clock_init(void)
{
    ret_code_t err_code = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for application main entry.
 */
int main(void)
{
    bool erase_bonds = false;

    // Initialize modules.
    log_init();
    clock_init();

    // Do not start any interrupt that uses system functions before system initialisation.
    // The best solution is to start the OS before any other initalisation.

#if NRF_LOG_ENABLED
    // Start execution.
    if (pdPASS != xTaskCreate(logger_thread, "LOGGER", 256, NULL, 1, &m_logger_thread))
    {
        APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
    }
#endif


    // Activate deep sleep mode.
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
    // Configure and initialize the BLE stack.
    ble_stack_init();

    // Initialize modules.
    timers_init();
    leds_init();
    gap_params_init();
    gatt_init();
    services_init();
    advertising_init();
    sensor_simulator_init();
    conn_params_init();
    peer_manager_init();
    application_timers_start();

    bsp_board_led_on(2);

    
    // Create a FreeRTOS task for the BLE stack.
    // The task will run advertising_start() before entering its loop.
    nrf_sdh_freertos_init(advertising_start, &erase_bonds);

    NRF_LOG_INFO("HRS FreeRTOS example started.");
    // Start FreeRTOS scheduler.
    vTaskStartScheduler();

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

So my question is, what is the proper way to do logging (whether using the NRF_LOG module or any other way) with the FreeRTOS OS? In particular, what is the proper way to log/debug in the timer/task contexts?

Thanks!

[NRF52840] Correct FreeRTOS logging using NRF_LOG module

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