How are pin default pull downs working?

[microbit-carlos]

On issue #357 we agreed that for V1 compatibility the pin pull downs should be enabled by default, as also discussed in #17.

Looking at NRF52Pin, it is probably achieved by having the default state in target.json/target-locked.json:

codal-microbit-v2/target.json

Line 26 in 3fa546f

"DEVICE_DEFAULT_PULLMODE":"PullMode::Down",

And that being applied in the NRF52Pin constructor. But this only sets the internal state of the NRF52Pin instance, it is only applied on first usage of get/setDigitalValue, when the setPull method is actually called:

• codal-nrf52/source/NRF52Pin.cpp#L154-L156

However the MicroBitIO constructor, which will be executed after all the NRF52Pins have been constructed, it sets the internal pull state of the edge connector pins to PullNone and applies it:

codal-microbit-v2/model/MicroBitIO.cpp

Lines 99 to 101 in 4f2aedc

	// Ensure all internal pins are configured with no pull resistors.
	for (int i=19; i<pins; i++)
	pin[i].setPull(PullMode::None);

So not 100% sure how the pull downs are configured by default.

[microbit-carlos]

Argh, as I re-read the issue, I notice that the loop is actually from pin19 forward, so we are good and there is no issue here 🙈