The timer library in the lib/hardware directory consists basically of two parts: an access module and a generic module that depends on one of the access modules.

The access module (in timer0.frt and timer1.frt) encapsulate the access to the selected timer. It uses interrupts to create a millisecond counter for common usage. This millsecond counter is a single cell variable timer0.tick that increments freely and wraps around every 65,5 seconds.

The counter is started with the command timer0.start. It automatically adapts to the actual controller clock rate.

The generic routines rely on this counter. A timer is simply a single cell number that is either the starting value of the millisecond counter (e.g. for elapsed) or the stop value (after).

To get a timer get the current value of the tick. With that number you can call elapsed to get the number of milliseconds since start. To check whether a timer is expired you need to calculate the end time by adding the time span to the current tick value. The word expired? compares the current tick value with that calculated time and leaves a flag.

The words are multitasker friendly (by calling pause whenever useful. The words provided so far are

  • expired? (t – flag) checks whether a timers has expired. calls

    pause internally.

  • elapsed (t – n ) gets the number of milliseconds since the timer

    has started.

  • ms ( u – ) alternative implementation of standard word ms

  • after (XT u –) waits u milliseconds and executes XT afterwards.

  • every (XT n – ) executes XT every n milliseconds. The XT has the stack

    effect ( – f) for f beeing a flag indicating whether or not terminating the every loop.

An usage example is the Loop With Timeout. It is used as an replacement for begin, and takes an number as the amount of milliseconds the loop has to finish, otherwise an exception is thrown.