RE: Unexpected serial UART bootloader exit mechanism

Pete W — Wed, 30 Mar 2022 09:44:58 GMT

Thanks for the reply Vidar and the explanation. That's exactly where I put my pull-up mod.

Regards

Pete

RE: Unexpected serial UART bootloader exit mechanism

Vidar Berg — Wed, 30 Mar 2022 08:07:36 GMT

Hello Pete,

The UART transport is configured to invoke the app_error_handler_bare() function in main.c if an UART Error condition is detected as you can see from the nrf_dfu_serial_uart.c source here:

And the error handler will trigger system reset making the device exit dfu mode.

A solution, as you suggested, is to enable the internal pull-up on the RX pin. This will prevent it from becoming floating when the USB port is not plugged in.

static uint32_t uart_dfu_transport_init(nrf_dfu_observer_t observer)
{
    ...

    err_code =  nrf_drv_uart_init(&m_uart, &uart_config, uart_event_handler);
    if (err_code != NRF_SUCCESS)
    {
        NRF_LOG_ERROR("Failed initializing uart");
        return err_code;
    }

    /* The UART driver configures the input pin without pullup enabled. We can override it 
       here after the driver initalization is complete. */
    NRF_P0->PIN_CNF[RX_PIN_NUMBER] |= (GPIO_PIN_CNF_PULL_Pullup << GPIO_PIN_CNF_PULL_Pos);
    
    ...

Best regards,

Vidar

RE: Unexpected serial UART bootloader exit mechanism

Pete W — Tue, 29 Mar 2022 16:53:55 GMT

(Device is nRF52811 and I'm using SDK 17.0.2)