RTEMS 4.6.0pre5 On-Line Library

Clock Driver Clock Interrupt Subroutine

BSP and Device Driver Development Guide

9.5: Clock Interrupt Subroutine

It only has to inform the kernel that a ticker has elapsed, so call :

rtems_isr Clock_isr( rtems_vector_number vector )
{
  invoke the rtems_clock_tick() directive to announce the tick
  if necessary for this hardware
    reload the programmable timer
}

BSP and Device Driver Development Guide