Re: [ECOS] periodic threads with kapi?

[Ryan Boder <icanoop at bitwiser dot org>]

On Sun, Aug 17, 2003 at 07:43:16PM +0100, Bart Veer wrote:
> >>>>> "Ryan" == Ryan Boder <icanoop@bitwiser.org> writes:
> 
>     Ryan> Is there a clean way to do periodic threads with absolute
>     Ryan> timing, as opposed to the relative timing you get with
>     Ryan> cyg_thread_delay()?
> 
> This should be easy enough using something like:
> 
> void
> my_thread_delay_absolute(cyg_tick_count_t abs_time)
> {
>     cyg_tick_count_t delay = abs_time - cyg_current_time();
>     if (delay > 0) {
>         cyg_thread_delay(delay);
>     }
> }
> 
> There is a possible problem if the current thread gets descheduled
> between the cyg_current_time() and cyg_thread_delay() calls, causing
> the thread to get delayed for longer than intended. You could avoid
> that by e.g. temporarily boosting the current thread's priority.


The problem still exists doing it that way. In fact that would even make it
worse.

The point is that I don't want to read the current time each period in my
thread. That causes drift.

I looked at the source code and I think it will be easy to add a correct
cyg_thread_absolute_delay(cyg_tick_count_t abs_time) to the kernel API. I
will be happy to write up a patch for it if the maintainers would consider
applying it.

-- 
Ryan Boder
http://www.bitwiser.org/icanoop

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