Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

rct42 — Tue, 08 Aug 2017 03:21:24 GMT

Hi,

I've managed to fix this problem (with the help of Nordic Semi!). It turned out that I needed to clear the errors before restarting the UART driver.

In case anyone else has a similar problem with the serial DFU, the modifications I made to nrf_serial_dfu.c are just in the uart_event_handler. When/if a framing error occurs (such as if RX goes low for longer than a character), it clears all errors and attempts to restart the UART interface.

static void uart_event_handler(nrf_drv_uart_event_t * p_event, void * p_context)
{
    switch (p_event->type)
    {
        case NRF_DRV_UART_EVT_TX_DONE:
            nrf_dfu_req_handler_reset_if_dfu_complete();
            break;

        case NRF_DRV_UART_EVT_RX_DONE:
            on_rx_complete((serial_dfu_t*)p_context, p_event->data.rxtx.p_data, p_event->data.rxtx.bytes);
            break;

        case NRF_DRV_UART_EVT_ERROR:
        {
            uint32_t err_code;
        
            /* Clear all events */
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_TXDRDY);
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_RXDRDY);
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_RXTO);
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_ERROR);
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_CTS);
            nrf_uart_event_clear(NRF_UART0, NRF_UART_EVENT_NCTS);
            
            /* Restart UART */
            err_code = serial_dfu_transport_close();
            if(err_code != NRF_SUCCESS)
            {
                APP_ERROR_HANDLER(err_code);
            }
            err_code = serial_dfu_transport_init();
            if(err_code != NRF_SUCCESS)
            {
                APP_ERROR_HANDLER(err_code);
            }
        } break;
    }
}

I recommend that Nordic Semi considers adding this to the next SDK release of nrf_serial_dfu.c or any drivers that use the UART driver!

EDIT:

While on the subject of making the nrf_serial_dfu.c more robust, I also had to reset the WDT in the wait_for_event() function in nrf_dfu.c. This is because my app (which uses the WDT) performs a software reset to get into the bootloader in preparation for DFU.

static void wait_for_event()
{
    // Transport is waiting for event?
    while(true)
    {
        NRF_WDT->RR[0] = WDT_RR_RR_Reload; //Reset WDT
        
        // Can't be emptied like this because of lack of static variables
#ifdef BLE_STACK_SUPPORT_REQD
        (void)sd_app_evt_wait();
#else
        __WFI();
#endif
        app_sched_execute();
    }
}

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

FormerMember — Wed, 02 Aug 2017 10:46:15 GMT

Could you run the chip in debug mode and check the UART-->ERRORSRC when this error occur? What is the source of the error given in that register?

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

rct42 — Fri, 28 Jul 2017 05:11:55 GMT

I've tried two attempts of recovering from this error:

Reinitialize the UART driver ("nrf_drv_uart_uninit" then "nrf_drv_uart_init"). Result: uarte_irq_handler triggers after a character is received, but is EVENTS_ERROR is set.
Call "nrf_drv_uart_rx_abort" by itself, then followed by "nrf_drv_uart_rx_disable" then "nrf_drv_uart_rx_enable". Result: uarte_irq_handler is not triggered after a character is received. This is despite no change in the interrupt register values from prior to pulling the RX pin low.

Both of these attempts were done in the NRF_DRV_UART_EVT_ERROR case in the "uart_event_handler".

Could someone please confirm that there is no way to recover from this error, other than performing a software reset?

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

rct42 — Fri, 28 Jul 2017 02:37:09 GMT

Another "fix" could be enabling the pull up on the NRF52's RX pin, this will at least get around the issue when the STM32 reboots.

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

rct42 — Fri, 28 Jul 2017 02:21:21 GMT

Kristin,

Just re-read your reply. I'm not sure whether this scheme would fix the problem. When the error occurs, it enters the "uarte_irq_handler" function in nrf_drv_uart.c which then calls the event handler that was passed into "nrf_drv_uart_init". In the case of the secure serial bootloader, this is the "uart_event_handler" function. In this function, I've commented out the NRF_DRV_UART_EVT_ERROR case so that the error is ignored (and the "uarte_irq_handler" clears the error flag). However, when a valid character is received, it is reported as an error in the "uarte_irq_handler" interrupt routine.

I'll see whether re-initialising the UART driver is able to fix the problem.

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

rct42 — Thu, 27 Jul 2017 21:57:03 GMT

Kirstin,

I'm sure I could make a work around on this on the STM32 side and will do so.

However, I'd also like to make the NRF52 firmware able to recover from this state. Any idea why the NRF52's UART sets the EVENTS_ERROR flag when a valid character is received after one EVENTS_ERROR is received from pulling the RX line low? This is despite the EVENTS_ERROR being cleared after it is first triggered in the uarte_irq_handler.

RE: Recover from NRF_UARTE_EVENT_ERROR when UART RX pin pulled low

FormerMember — Thu, 27 Jul 2017 12:13:34 GMT

Is there a way for STM32 to indicate that it is about to reset? If so, STM32 can tell nRF52 that it is a about to reset. The nRF52 can then set a flag so that the application knows that it can ignore the error NRF_DRV_UART_EVT_ERROR.