Artemis ATP pins set to INPUT_PULLUP seem to float when interrupt attached

Development Boards Artemis
1

I have an Artemis ATP and I’m experiencing a really confusing. Here’s the simplest test case I’ve been able to write to reproduce the issue. For context, I’m testing this with no wires connected to the pins.

void setup() {
	Serial.begin(9600);
	pinMode(D4, INPUT_PULLUP);

	// attachInterrupt(D4, [](){}, FALLING);
}

void loop() {
	Serial.println(digitalRead(D4));
	delay(100);
}

The above code pulls D4 to HIGH and produces the following output, as expected:

1
1
1
1
1
...

If I uncomment the attachInterrupt line, then I get output that looks like this:

1
0
0
1
0
1
1
0
...

It looks like the pin begins floating. Again, this is all with no wires connected to any pins. Is there some consideration I’m not aware that I need to be making in this very simple example?

Additionally, if I put a Serial.writeln() call in the interrupt, I find that it’s being called constantly, again with no wires attached.

2

If you’re referring to my lack of use of digitalPinToInterrupt(), I can assure you that’s just a transposition error. I was using it in my sketch. If that’s not what you’re referring to, can you elaborate further?