Wakeup from sleep with GPIO

[Marco Russi]

Hi, I would like to put a nrf51822 device into system off mode and wake it up with a GPIO transition from high to low. I would like to measure the press time of the button after wake up but it seems that software doesn't run properly until the button is pressed. So, does the software run normally after the reset transition even if the button is still pressed? I hope it is clear. Thanks.

[RK]

Well the software doesn't run properly until the button is pressed because it's off. After you press the button and the chip resets then of course it will run normally, from the very start of your code. If you want to measure the press time of the button, then you'll have to detect at the start of your code if the button is currently pressed and start timing it, and you'll miss the time it takse for the system to reset itself.

[RK]

I no-longer really understand what you're asking. I can't confirm if the software runs after wake up, it's your code. You say the timer starts running after reset if the level is low, so that would mean that it's running. If you have the wake up configured correctly then the first press will wake the chip up and start your code. So if you're not seeing that, either you have the wake up configured incorrectly and the chip doesn't wake until the second button press, or you have a problem in your code which doesn't actually start the timer running on reset if the pin is low even though it's supposed to. All I can say is that the chip will reset on whatever GPIO event you have configured to wake it up and it will then instantly start running whatever code you have on it.