SAM3S backup mode wakeup

Discussion around product based on ARM Cortex M3 core.

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SAM3S backup mode wakeup

Wed Jul 23, 2014 8:07 pm

I am having an issue waking up from backup mode. I have a button on PA0 (WKUP0). I am using the internal pull-up for this button and when the button is pressed, the line is connected to GND.

I have the following code:
SUPC->SUPC_WUIR = (1 << 16);
That code should wakeup the processor when the WKUP0 pin goes from high (pull-up) to low. This does not work as expected. However....
SUPC->SUPC_WUIR = (1 << 16) | 1;
The above code - which makes the processor wake up on a high on WKUP0 - works as expected. Although in this case I have to hold the button down until the sleep timer expires and the release the button to wake up the processor.

Any idea on why it would work from low to high transitions but not high to low???


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