Timers & Counters

The Automaton timers & counters are implemented as classes with a similar interface. Timers and counters are used a lot in state machines. Machines like Atm_led & Atm_fade run almost entirely on them.

atm_timer_millis class

A millisecond timer that starts running from the moment a state change occurs and expire() at the set() number of milliseconds. The timer will expire immediately when set to zero and will never expire when set to the value ATM_TIMER_OFF. The maximum effective timer value that can be used is 4,294,967,294 ms (about 49.7 days)

A timer doesn't need to be reset when a state change occurs. The reset will be automatic because the state timer resets and the timer is relative to the current state timer. The atm_timer_millis class can handle a millis() rollover. To create intervals greater than 4,294,967,294 ms (about 49.7 days) you should combine a timer with a counter. That should take you well beyond the expected lifetime of your microcontroller.

atm_counter class

An atm_counter object counts down from the set() value to 0. The counter will ignore decrement() calls and will never expire() when set to the value ATM_COUNTER_OFF. Counters are 16 bit unsigned integer values and the highset value is reserved for the ATM_COUNTER_OFF flag, so the maximum value that can be counted is 65534.

• set()
• decrement() (Counters only)
• expired()

void set( uint32_t v )

Sets a timer or counter to a value.

In the Atm_* class definition:

atm_timer_millis timer1;
atm_counter counter;

In the Atm_*::begin() method:

timer.set( 10000 );  // Set timer to a 10 seconds delay
timer.set( 0 );  // Set timer to expire immediately
timer.set( ATM_TIMER_OFF );  // Set timer not to expire at all

counter.set( 10 ); // Set counter to expire after 10 decrements
counter.set( 0 ); // Set counter to expire immediately
counter.set( ATM_COUNTER_OFF ); // Set counter not to expire at all

int expired( void )

Alternatively: int expired( Machine & machine )

Returns 1 if a timer or counter has expired and 0 if it has not. (which happens to be exactly what the event() handler needs)

The timer version of expired() requires a machine reference as parameter (to access the state timestamps).

  switch ( id ) {
    case EVT_TIMER1 :
      return timer1.expired( this );
    case EVT_TIMER2 :
      return timer2.expired( this );
    case EVT_COUNTER :
      return counter.expired();
  }

uint16_t decrement( void )

(Counters only)

Decrements a counter. (typically done inside the action() handler)

  counter.decrement();