_modify:
  TIFR?:
    access: read-write

TCCR?B:
  _modify:
    CS?:
      _write_constraint: enum
  CS?:
    _replace_enum:
      NO_CLOCK:      [0, "No clock source (Timer/Counter stopped)"]
      DIRECT:        [1, "Running, No Prescaling"]
      PRESCALE_8:    [2, "Running, CLK/8"]
      PRESCALE_64:   [3, "Running, CLK/64"]
      PRESCALE_256:  [4, "Running, CLK/256"]
      PRESCALE_1024: [5, "Running, CLK/1024"]
      EXT_FALLING:   [6, "Running, ExtClk Tx Falling Edge"]
      EXT_RISING:    [7, "Running, ExtClk Tx Rising Edge"]