current consumption with uarte0 and rtc2 in system on mode

[eleven-x_devteam]

Hi,

I am working on low power mode with DK to apply optimization to our project.

And I verified DK with ble_uart_app can go down to less than 5uA in system on mode which is good result. (current consumption was measured at P27 Li-Po 3.0v)

(https://devzone.nordicsemi.com/f/nordic-q-a/52921/low-power-system-on-mode-in-ble_uart_app)

Also it can go down to similar level with our customized app and uart0 disabled and RTC2 disabled. (uarte0 for debug log and commands from PC, RTC2 for our os time)

Here are some questions.

#1. In system on mode, if I keep uarte0 on, it raises current by around 180uA. Then for low power, it needs to be off.

However, our device should wake up by PC commands via uart even in sleep mode (system on).

Could you recommend something to try to lower power with keeping uart alive which is available to wake up by uart trigger?

If so, could you let know some example for it?

#2. I am using 32768 Hz for RTC2 prescaler and RTC2 also adds up the current hundreds of uA in system on mode. 

And when I change prescaler to lower freqeuncy, it can go down to less than 5uA.

But our os time code still needs to use full scale so I am considering like using RTC2 with full scale in normal mode and turing off RTC2 in system on mode after saving tickcount , start app_timer with low prescaler and then udpating rtc tick with sleep time when device wakes up.Does it make sense? or Could you recommend some better way?

Thank you.

[Dmitry]

Hi,

#1  You can configure GPIO pin sense to wake by low level on RX pin. Start bit of the first byte will serve as wake-up signal, then you can route EVENTS_PORT to TASKS_STARTRX. I'm not sure that UART receiver will be in time to catch first byte, if not, you can send 0xff as wake-up command and ensure delay for one bit (or wait for '1' on RX) before starting UART peripheral to avoid synchronization issues.

#2  Maybe you can configure your OS to use SYSTICK timer? Then RTC2 could be run always at lowest frequency. Of course your way also makes sense.

[eleven-x_devteam]

Hi,

Thank you for the answer.

About #1, as expected, it doesn't work after waking up without any code change so I've tried to send 0xff as wake-up command to give some delay and actually it worked without low power mode (system on), but when I turn on the system on mode, it seems the device are missing more than one byte and never recovered.

I am using the code below for enabling/disableing uart0 but nrf_serial_init() might be not fast enough to catch rx data even after 0xff.

So I've tried to use nrf_drv_uart_init instead but uart doesn't even start with this.

Do you any suggestion or any sample code for this?

--------------------------------------------------------

[uarte0 disble and set rx irq]

    nrf_serial_uninit();

    *(volatile uint32_t*)0x40002FFC = 0;

    *(volatile uint32_t*)0x40002FFC;

    *(volatile uint32_t*)0x40002FFC = 1;

    if (!nrf_drv_gpiote_is_init())

    {

        nrf_drv_gpiote_init();

    }

    nrf_drv_gpiote_in_uninit(RX_PIN_NUMBER);

    nrf_drv_gpiote_in_config_t config;

    config.is_watcher = false;

    config.hi_accuracy = false;

    config.pull = NRF_GPIO_PIN_PULLUP;

    config.sense = NRF_GPIOTE_POLARITY_HITOLO;

    nrf_drv_gpiote_in_init(RX_PIN_NUMBER, &config, int_pin_fall_handler);

    nrf_drv_gpiote_in_event_enable(RX_PIN_NUMBER, true);

[uarte0 enable]

   nrf_serial_init();

[Sigurd]

eleven-x_devteam said:

but when I turn on the system on mode, it seems the device are missing more than one byte and never recovered.

Do you mean System OFF mode here?

eleven-x_devteam said:

I've tried to send 0xff as wake-up command to give some delay

Are you able to add some more delay? You could also try to lower the baudrate, and see if that helps.

[eleven-x_devteam]

Hi,

Thank you for the reply.

We were using 115200 and lower baud rate like 38400 can fix this but it's too slow.

So I've tried again to add more delay with another byte and some tweak at our os code then it was fixed.

Here is one more question about RTC.

I've checked again power consumption of RTC.

We enabled RTC2 for os tick count and the sleep current is around 200uA with enabling rtc2 but when I change os tick reference to RTC1 ( even with 32K), using app timer and turn off RTC2, then the sleep current is around 5uA with enabling RTC1.

I wonder if power consuming could be different between each channel of rtc

Thank you.

[Sigurd]

eleven-x_devteam said:

We enabled RTC2 for os tick count and the sleep current is around 200uA with enabling rtc2 but when I change os tick reference to RTC1 ( even with 32K), using app timer and turn off RTC2, then the sleep current is around 5uA with enabling RTC1.

Are you sure that RTC2 and RTC1 has the same configuration ?

What OS are you using ?