Setting up the AVR analogue comparator registers

gistfile1.c

  // Set up the comparator.
  pinMode(AIN0, INPUT);
  pinMode(AIN1, INPUT);
  // ACI : Ana Comp Interrupt flag - writing a 1 clears it, hardware autoclears it when calling ISR
  // ACIE : Ana Comp Int Enable
  // ACIS1, ACIS0 : Ana Comp Int mode select:
  //   0      0     Int on output toggle
  //   0      1     Reserved
  //   1      0     Int on falling output edge
  //   0      1     Int on rising output edge
  // (See section 16 of ATTiny85 datasheet)
  ACSR = 0 | (1 << ACI) | (1 << ACIE) | (1 << ACIS1);  // Enable interrupts; falling edge mode.