If ANYONE has a better approach for getting the bit# from bitvalue in digitalPinToPCMSKbit(), please tell me... It looks awful.

Does this help: http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightLinear

I was looking for some builtin, always available function I could use in the define.
Maybe have to put some simple rotate-carry-out loop somewhere in the base libs.

Found the builtin:
__builtin_ctz() -> "count trailing zeroes"

Looks much better now ;)

Really nice jayzakk! I actually needed to use the timer 3 interrupt some time ago and gave up, thanks for this!

Did you test the Analog Comparator (page 224 of datasheet v1.0.4) ?

Nope, didn't have a setup or example for it.

This was marked as "todo" in the original core on which this one is based, (in the readme). This part in your PR should have covered it, right?

#define ANALOG_COMP_0_vect      _VECTOR(23)
#define ANALOG_COMP_1_vect_num  25
#define ANALOG_COMP_1_vect      _VECTOR(25)

When I try to compile my skech I get these error:

c:\ ... variants\standard\pins_arduino.h:392:47: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
const uint8_t PROGMEM port_to_PCMSK_PGM[] = { (uint8_t *)0, (uint8_t *)0, &PCMSK0, &PCMSK1, &PCMSK2, &PCMSK3, &PCMSK4 };

Maybe in line 404, need some conversion about &PCMSKx
I don't know what, but I'm tired now, Perhaps tomorrow I can figure out.

Edit: My mistake: pins_arduino.h was not the newest one. When I use the correct version of this file, I get another error.
redefined: digitalPinToPCMSK, digitalPinToPCICRbit, digitalPinToPCMSKbit and digitalPinToPCICR