I thought it would be easy to couple a button to my Arduino Gemma.
However, it just didn't work. I've read the whole page on attachInterrupt but apart from a hunch that maybe some pins can't be used for interrupts, I got nothing.
So I had to dive into the code, where I found this little snippet (Arduino.h)
#define NOT_AN_INTERRUPT -1
And in $HOME/.arduino15/packages/arduino/hardware/avr/1.8.5/variants/gemma/pins_arduino.h, I read this:
#define digitalPinToInterrupt(p) \
((p) == 2 ? 0 : NOT_AN_INTERRUPT)
So here's an idea for you: add a little snippet to your sketch:
template<int PIN>
constexpr int interruptFor() {
constexpr auto i = digitalPinToInterrupt(PIN);
static_assert(i != NOT_AN_INTERRUPT,
"board can't use this pin for an interrupt");
return i;
}
And use this function instead:
namespace my_wiring {
constexpr auto BUTTON_PIN = 2;
}
constexpr auto BUTTON_INTERRUPT =
interruptFor<my_wiring::BUTTON_PIN>();
Now, on my Gemma (with an ATtiny85), when I change my BUTTON_PIN to e.g. 1:
sketch_aug14a.ino: In instantiation of
'constexpr int interruptFor() [with int PIN = 1]':
sketch_aug14a/sketch_aug14a.ino:19:70: required from here
sketch_aug14a/sketch_aug14a.ino:11:3: error: static assertion failed:
board can't use this pin for an interrupt
static_assert(i != NOT_AN_INTERRUPT,
^~~~~~~~~~~~~
That would have been a time saver! Maybe I'll propose to introduce this in the arduino headers, too. When I have time.
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