[Adeos-main] Re: Porting to Intel IXP425

["Schlägl Manfred jun." <manfred.schlaegl@domain.hid>]

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Am Freitag, den 30.03.2007, 16:41 +0200 schrieb Gilles Chanteperdrix:
> Richard Cochran wrote:
> >>The timer is aperiodic (most of the time) when running Xenomai, so
> >>__ipipe_mach_set_dec is called for each timer tick and programs the
> >>timer hardware for the next tick.
> > 
> > 
> > Okay, so does that mean that I should implement a "one-shot" timer, or
> > are we talking about resetting the periodic timer once in a while?
> > 
> > (BTW, in one-shot mode, the IXP425 timer does not do what the Developers
> > Manual, part 252480-006, says that it does!)
> 
> Yes, the one shot mode is Xenomai default mode. The implementation of a
> periodic timer over the one-shot timer is already done by the generic
> ARM part of the Adeos patch.

It's better to use a periodic implementation in background, because then
you are able to messure the lost ticks between a timer-interrupt and
programming next timer-event.

Example with 16bit timer:
 * Periode: 27000 Ticks 
 * Timer counts down to zero (Interrupt) & wrap around to 2^16-1 
 * Reprogramm Timer with new Periode (lost-ticks = 2^16 - timerval)

These lost-ticks should be added to the global time-stamp (returned by
get_tsc) and should mentioned at the linux-gettimeoffset-function also.


Lost-ticks could sum up to a bothering time-error.

- Manfred Schlaegl


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