enable external interrupt!

pin 9: PWM (analogWrite 8-bit PWM)
pin 10: SPI SS
pin 11: SPI MOSI
pin 12: SPI MISO
pin 13: SPI SCK
pin 3: external interrupt (attachInterrupt)
/usr/share/arduino/Arduino.mk

OLIMEX:

note: CPU is ATMEGA32U4-AU
note: D13 is UEXT #CS
note: D14 is MISO
note: D15 is SCK
note: D16 is MOSI
note: D3 is INT0
note: D11 is PCINT7