Timer driver vs. timer manager, etc.

Joel Sherrill joel.sherrill at OARcorp.com
Thu Jun 5 18:36:03 UTC 2003

Kenneth Peters wrote:
> I want to make sure I understand the timer and clock elements of RTEMS
> correctly, since some of the same terms are used in different places, with
> no real connection between them (I think). Please comment on the following:
> The "Timer Driver" referred to in the "BSP and Device Driver Development
> Guide" is only used by the provided OS test suite, and has nothing to do
> with the "Timer Manager" from the "RTEMS C User's Guide".

Yes.  NOTHING uses the Timer Driver except the Timing Test Suites.

> The "Timer Manager" does need the "Clock Driver" from the "BSP and Device
> Driver Development Guide", as does the "Clock Manager".


> The "Rate Monotonic Manager" needs the "Timer Manager" and thus the "Clock
> Driver" (or does the RMM use the "Clock Driver" directly?). The "Task
> Manager" needs the "Timer Manager" (or does the Task Manager use the "Clock
> Driver" directly?) only if timeslicing or delay functions are needed?

All timing services in RTEMS are based upon the Clock Driver.  The Timer
Manager is not required except to run the Timing Test Suites.  

> The "Real-Time Clock Driver" from the "BSP and Device Driver Development
> Guide" is not actually required for anything. If it is provided, the user
> can call its functions to synchronize the "Clock Manager" and the RTC
> device, or as substitutes for some of the "Clock Manager" functions.


> Thanks,
> Ken Peters

Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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