RTEMS Ada User's Guide
For the features provided by the clock manager to be
utilized, periodic timer interrupts are required. Therefore, a
real-time clock or hardware timer is necessary to create the
timer interrupts. The rtems.clock_tick
directive is normally called
by the timer ISR to announce to RTEMS that a system clock tick
has occurred. Elapsed time is measured in ticks. A tick is
defined to be an integral number of microseconds which is
specified by the user in the Configuration Table.
RTEMS Ada User's Guide
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