RTEMS C User's Guide
A timer is an RTEMS object which allows the
application to schedule operations to occur at specific times in
the future. User supplied timer service routines are invoked by
the rtems_clock_tick directive
when the timer fires. Timer service routines may perform
any operations or directives which normally
would be performed by the application code which invoked the
rtems_clock_tick directive.
The timer can be used to implement watchdog routines which only fire to denote that an application error has occurred. The timer is reset at specific points in the application to insure that the watchdog does not fire. Thus, if the application does not reset the watchdog timer, then the timer service routine will fire to indicate that the application has failed to reach a reset point. This use of a timer is sometimes referred to as a "keep alive" or a "deadman" timer.
RTEMS C User's Guide
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