NRF9160 power off and wake up

[XavierN]

Hello, this is a follow up on this ticket: https://devzone.nordicsemi.com/f/nordic-q-a/84834/protecting-the-battery-via-sleep-mode

Our goal is to switch off the device (based on nrf9160) when battery voltage is under a threshold and wake it up (reboot) upon external power connection.

Our setup is a board with battery input. We have connected the USB line to GPIO 14 to be able to detect power input (this is working as explained below).

We were told (see ticket linked above) to mimic this example: https://github.com/nrfconnect/sdk-zephyr/tree/main/samples/boards/nrf/system_off

Our very simple POC:

void main(void)
{
    printk("Power off POC started\n");

    nrf_gpio_cfg_input(DT_GPIO_PIN(DT_NODELABEL(external_power_detection), gpios), NRF_GPIO_PIN_NOPULL);
    nrf_gpio_cfg_sense_set(DT_GPIO_PIN(DT_NODELABEL(external_power_detection), gpios), NRF_GPIO_PIN_SENSE_HIGH);
    // k_sleep(K_SECONDS(1));
    // pm_power_state_force(0u, (struct pm_state_info){PM_STATE_SOFT_OFF, 0, 0});

    int v;
    int acc = 0;
    int seconds = 0;

    while (1) {
        v = nrf_gpio_pin_read(DT_GPIO_PIN(DT_NODELABEL(external_power_detection), gpios));
        printk("Input value: %d\n", v);
        acc += v;
        seconds++;
        printk("Input high %d times, seconds passed: %d\n", acc, seconds);
        k_sleep(K_SECONDS(1));
    }
    
    
    
}

Running this example, we read the USB connected PIN every second, we keep track of the seconds. While USB is connected the accumulator and the number of seconds keep in sync, disconnecting the USB for a few seconds, the application keeps running because of the battery. Then we connect the USB again to get access to the console and we can verify that the accumulator has remained unchanged while the seconds passed have continued to increase. Example of output:

*** Booting Zephyr OS build v2.7.99-ncs1-1  ***
Power off POC started
Input value: 1
Input high 1 times, seconds passed: 1
Input value: 1
Input high 2 times, seconds passed: 2
Input value: 1
Input high 3 times, seconds passed: 3
Input value: 1
Input high 4 times, seconds passed: 4
Input value: 1
Input high 5 times, seconds passed: 5
Input value: 1
Input high 6 times, seconds passed: 6
Input value: 1
Input high 7 times, seconds passed: 7
[Disconnected]
[Connected]
Input value: 1
Input high 9 times, seconds passed: 15
Input value: 1
Input high 10 times, seconds passed: 16
Input value: 1
Input high 11 times, seconds passed: 17

This verifies that power detection is working. Now for the switch off/wake up part. In the example we were given, we find nowhere how to link the input event to a "wake up callback", nevertheless, if we uncomment  these lines from the POC example:

    // k_sleep(K_SECONDS(1));
    // pm_power_state_force(0u, (struct pm_state_info){PM_STATE_SOFT_OFF, 0, 0});

And run it , the unit does switch off, but when disconnecting and connecting power again, it keeps being off (remember that power is maintained through all the process thanks to the battery)

Our question is, how to instruct the device to wake up or reboot upon input activation?

Thank you.

Xavier

[Elfving]

Hello again Xavier,

Nice testing!

In the example we were given, we find nowhere how to link the input event to a "wake up callback"

Right, when using the lowest power state "PM_STATE_SOFT_OFF" there is no need for it. The contents of system(CPU and memory) will not be preserved, so the system will be restarted as if from an initial power-up and kernel boot either way. 

If you'd want a wake-up callback you could always go for another power state, but I got the impression that you wanted to do a reboot either way? The documentation on the sample offers some more info on eg. RAM retention, in case that is relevant for you.

Our question is, how to instruct the device to wake up or reboot upon input activation?

I will have to get back to you on this, as I have some concerns here.

Btw, what NCS version are you using?

Regards,

Elfving