Larger power consumption when the display is not cleared before uBit.power.off()

[microbit-carlos]

When something is shown in the display and we go into "power off" mode in battery power, we see a much larger power consumption.

We expect an average of around 35 uA @ 3.0V, but in this case we see around 850 uA.

Simply running uBit.display.clear() before uBit.power.off() resolves the issue, so we probably have some event running on the background to do with the display pins.

#include "MicroBit.h"

MicroBit uBit;

int main() {
    uBit.init();

    uBit.display.printChar('X');
    uBit.sleep(100);
    // uBit.display.clear();    // <-- Uncommenting this fixes the power consumption

    while (true) {
        if (uBit.buttonA.isPressed()) {
            uBit.sleep(500);
            uBit.power.off();
        }
        uBit.sleep(100);
    }
}

It's quite possible this might be a side effect of 03c05e2 from PR #366, so we might have to look into a way to ensure the pin events are disabled without disabling GPIOTE completely.

[microbit-carlos]

Looking at the time between high current peaks confirms that we have something running on a 4ms interval: