Delay setting RTEMS clock with TOD_Set.

[Gedare Bloom]

I guess this is in the rtems_clock_set routine that the TOD_Set is called? [1]

My best guess is that the granularity of the time is quite coarse, so
you are seeing some rounding errors based on when in the current
"tick" the TOD_Set is called. For example, look at lines 51-53:

    newtime.tv_sec = _TOD_To_seconds( time_buffer );
    newtime.tv_nsec = time_buffer->ticks *
      rtems_configuration_get_nanoseconds_per_tick();

The fine-grained resolution of time (nanoseconds) is approximated by
the number of ticks times the configured ns per tick. By default this
is going to be about 10 milliseconds per tick, so you would expect on
average about 5 ms difference between the actual time and the
approximated time.

[1] http://git.rtems.org/rtems/tree/cpukit/rtems/src/clockset.c?id=4.10.2

-Gedare

On Wed, Apr 10, 2013 at 6:00 AM, Rafael Morales <rmorales at iaa.es> wrote:
> Dear all,
>
> We are using a development system based on Leon3 at 25MHz clock and RTEMS
> 4.10 (Gaisler version 4.10.1.2.8).
>
> We are experiencing a big delay setting the clock time with TOD. The
> sequence is:
>
>      struct timespec startTimeStamp;
>     get_time_stamp(&startTimeStamp);
>
>     _Thread_Disable_dispatch();
>     _TOD_Set( newtime );
>     _Thread_Enable_dispatch();
>
>     struct timespec stopTimeStamp;
>     get_time_stamp(&stopTimeStamp);
>
>
> If we get the new time after the _TOD_Set, we see that current time as about
> 1-5 milliseconds late. We have try to delete the _Thread_Disable_dispatch
> and _Thread_Enable_dispatch with no results. It seems that the call _TOD_Set
> is the responsible of the delay
>
> Any idea about how to manage this situation?
>
> Thanks in advance.
>
>> Hi,
>>
>> here is the proof for the patched hello world on the sis target and the
>> patch generated by git. I hope it's okay.
>>
>> I also got a first draft of the proposal, so the question is: Who wants to
>> read it?
>>
>> Regards,
>> Philipp
>>
>>
>> screenshot:
>> https://wwwpub.zih.tu-dresden.de/~s8940405/gdb_hello_world.png
>>
>> patch:
>>
>> https://wwwpub.zih.tu-dresden.de/~s8940405/0001-hello-world-gsoc-2013-fix.patch
>> _______________________________________________
>> rtems-users mailing list
>> rtems-users at rtems.org
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>>
>>
>
>
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