Hi, The 20us are just the ISR duration; the latency time is not included.
Thanks Patrick -----Message d'origine----- De : Gilles Chanteperdrix [mailto:[EMAIL PROTECTED] Envoyé : jeudi, 25. octobre 2007 19:48 À : Patrick Cc : [email protected] Objet : Re: [Xenomai-help] Event flag from ISR Patrick wrote: > Hi all, > > > > I am using a RT event flag structure to start a task from an ISR. > > The task waits on rt_event_wait and when the IRQ occurs the ISR executes > rt_event_signal (the ISR code only clears the flag and calls > rt_event_signal). > > I'm using an oscilloscope to measure the length of the ISR and the first > occurrence lasts about 20us and all the next occurrences last about 4us. > > > > My question is why the first ISR is so long? > > > > For information I use xenomai 2.4 rc4 on ARM pxa270 machine with 2.6.20 > kernel. Typical worst case interrupt latency on ARM is around 50 us, so 20 us is not that long. What you are observing is probably a cache effect. In this case, you should observe 20us after each user-space context switch since on ARM, cache is flushed at each user-space context switch. -- Gilles Chanteperdrix. _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
