Thank you for this clue.
Sebastien
Klaas Gadeyne a ecrit :
> > oneshot mode. Periodically, the next wake up date is calculated in clock
> > units. Because the period in clock unit is not equal to the period in
> > nanoseconds, a drift should be seen, especially after a large number of
> > periods.
> >
> > In fact, after having done this test, I did not see such a drift. Do not
> > think I am disapointed, I'm not ! I would like to know wether I am wrong
> > in my assumptions or not, and if not, how the gethrtime function manages
> > not to create a drift.
>
> I don't know wether you're wrong in your assumptions but a couple of weeks
> ago I was working on some steppermotor software and there there was
> obviously some drift when just using a call (for constant speed)
>
> while(1)
> {
> pthread_make_periodic_np(pthread_self(),gethrtime()+period,0);
> pthread_wait_np();
> outb(...);
> }
>
> I don't know wether the drift is due to the rounding process, but the
> jitter alone is responsible for drift.
>
> To avoid drifting errors you can use "absolute timing", ie something like
>
> next_fire_time = somewhere in the future;
> while(1)
> {
> pthread_make_periodic_np(pthread_self(),next_fire_time,0);
> pthread_wait_np();
> outb(...);
> next_fire_time += period;
> }
>
> Hope this was somewhat an answer to your question,
>
> regards
>
> klaas
>
> -- [rtl] ---
> To unsubscribe:
> echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR
> echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED]
> --
> For more information on Real-Time Linux see:
> http://www.rtlinux.org/rtlinux/
-- [rtl] ---
To unsubscribe:
echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR
echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED]
--
For more information on Real-Time Linux see:
http://www.rtlinux.org/rtlinux/
