Timed routines

[janovetz at tempest.ece.uiuc.edu (Jake Janovetz)]

We had some discussion of this sometime ago.  I actually like
the proposed method since this is how most of my TSRs get
written anyhow.  I write some new task and have it wait for
evens from a timer task.  The timer task just sends an event
to the waiting task.

For some reason, Joel was opposed to the change, I think.  Joel?

    Cheers, 
    Jake


On Mon, Oct 04, 1999 at 08:34:55AM -0600, Eric Norum wrote:
> I'd like to propose a change to the way RTEMS handles timers.
>   
> Although it's not really mentioned in the documentation (at least not
> anywhere that I could find), timed routines run in the context of the
> clock interrupt service routine.  I propose changing this so that timed
> routines run in the context of a timer task.  The clock interrupt
> handler (rtems_tick_handler) would then update the time value and send
> an event to the timer task which would do the callouts to the timed
> entries.
> 
> For example, the _Watchdog_Tickle_ticks routine could decrement a
> `ticks-till-next-timed-entry' counter and send an event to the timer
> task when the counter reached 0.  The timer task would then reset the
> `ticks-till-next-timed-entry' counter and perform the required
> callbacks.
> 
> There would be two more configuration parameters associated with the new
> scheme.
> 1) The priority at which the timer task would run (perhaps 1 or 2 by
> default)
> 2) The stack size of the timer task.
> 
> Good things resulting from the change:
>         Interrupt latency would be reduced since the processor would
>         spend less time in the clock interrupt handler.
>         Timed routines would be able to call on any service, including
> 	network I/O.
> 
> Bad things:
> 	Somewhat more overhead in processing timed routines.  The overhead
> wouldn't
> 	be that high, though, since the event would be sent to activate the
> timer
> 	task only when a callout was due.
> 
> -- 
> Eric Norum                                 eric at cls.usask.ca
> Canadian Light Source                      Phone: (306) 966-6308
> University of Saskatchewan                 FAX:   (306) 966-6058
> Saskatoon, Canada.

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