Re: [Xenomai] rt_task_sleep_until() miss release point?

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Fri, Nov 07, 2014 at 09:25:21AM +0000, ZIV-Alberto Ozalla Cantabrana wrote:
> 
> On 06/11/14 21:22, Philippe Gerum wrote:
> > On 11/06/2014 05:46 PM, ZIV-Alberto Ozalla Cantabrana wrote:
> >> Hi,
> >>
> >> These are the simplest examples:
> >> There are no MSW for Test_Task.
> >> The goal is to increment counter_ms each millisecond.
> >>
> >> Given that:
> >> 1000000 nanoseconds = 24000 tsc.
> >> 1 tsc = 41 ns
> >>
> > Is rt_timer_ns2tsc(1000000) actually returning 24000 on your platform?
> > Yes.
> >> void Test_Task(void *arg)
> >> {
> >>     rt_task_set_mode(0, 0, NULL);
> > This is useless and not recommended. A newly created task always starts
> > in primary mode.
> >
> > Ok. I will delete it.
> >>      while (1) {
> >>
> >>              unsigned long long before = counter_ms;
> >>              usleep(1000000);    // 1 second.
> > Although this would rather cause higher count values, this non-rt main
> > using a non-rt sleep service won't give you an accurate delay for the
> > measurement.
> >
> > It is only an example.

The problem is that so far, you have not been able to provide a
correct example which provides a proof of what you are saying. It
does not mean that what you say is wrong, just that we have reasons
to doubt it.

Anyway, I do not think you can assume that
rt_timer_tsc2ns(rt_timer_tsc()) is the same thing as
rt_timer_read(), I would say the first is equivalent to POSIX
CLOCK_MONOTONIC whereas the second is equivalent to CLOCK_REALTIME,
so, there is an offset between the two.

What rt_task_sleep_until expects, is what rt_timer_read() returns

To check that, right after the call to rt_task_sleep_until, call
rt_timer_read (and not rt_timer_tsc), and see if it is near t2. You
can use rt_printf in a real-time task to avoid switches to secondary
mode.

Also, are you running the native skin timer in periodic or aperiodic
mode?

-- 
					    Gilles.