How to turn off completely UART in nRF52840

[Elisa]

Hello, I’m using nRF52840 with SDK 16 and SD 7. My purpose is to save as much power is possible using high-frequency clock (32MHz) only during periodic duties and BLE activity and low-frequency clock (32KHz crystal) otherwise. I’ve programmed app-timer and app-scheduler: if I use only I/O the sleep time power consumption is about 3uA. If I power-on UART with FIFO all the time, power consumption is about 1mA. So I need to power UART only when code uses it in app-scheduler event handler: I invoke app_uart_init() and app_uart_close() after few milliseconds every 1s, but unfortunately the power consumption is 1mA all the time. Apparently, app_uart_close() doesn’t power-off the UART; I follow various post in this blog with no success.

Thank you

Elisa

[Vojislav]

Hi Elisa,

I had similar problem when working with nrf52811. I was using SDK 15.3 and I was testing this on nRF52840, so it should also work for you. 
https://devzone.nordicsemi.com/f/nordic-q-a/58745/uart-disable-problem
Check the verified answer. 

Best regards,
Vojislav.

[Elisa]

Thank you Vojislav, but it’s not the same case. I don’t power on/off the UART in BLE events, but in a similar way in a callback invoked by app-scheduler and the scheduled event is generated by an app-timer periodic callback:

 

/**@brief Periodic handler function to be called by the scheduler. */

void periodic_scheduler_event_handler(void *p_event_data, uint16_t event_size)

{

    char string[] = {'\0', '\0', ':', '\0'};

    nrf_gpio_pin_toggle(LED_1);

        

    byteToHex(counter, string);

    uart_init();

    app_uart_putstr(string, 4);

    app_uart_close();

       

    counter++;

}

 

/**@brief Timeout handler for the repeated timer used for toggling LED 1.

*

* @details Print a log line indicating weather executing in thread/main or interrupt mode.

*/

static void timer_handler(void * p_context)

{

    app_sched_event_put(NULL, 0, periodic_scheduler_event_handler);

}

 

I still need a feedback.

[Einar Thorsrud]

Hi,

You could try to toggle the power tot he UARTE peripheral by writing to a hidden register as described in this post.