Re: next_period = start + n*period; versus next_period = next_period+period;

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 27 Oct 2004 08:46:29 -0500, Mark H Johnson wrote:

> Dmitry A. Kazakov wrote:
> 
>> [snip]
>> 
>> Right. However there could be other issues to consider:
>> [snip]
>> 
>> 2. What happens when the task misses a deadline? Usually it should skip one
>> "tick" and go to the next one.
>>
> Maybe yes, maybe no. I have built several system where if you run long 
> in one frame, you try to catch up the next one. For example, I may have 
> an 80 Hz task running. It is connected to a 1553 bus where at 1 Hz, I 
> get more messages than any other 80 Hz frame. If I overrun that one 
> frame (out of 80), I don't mind running the next frame a little late.
> 
> It all depends on the application being designed and the safety (or 
> accuracy) considerations of that design.

Yes, if you change the requirements. (:-)) However, surely, it is
questionable whether jitter and even more so, a small absolute time lag is
a real issue in say 80-100% cases. In my ignorance I always had an
impression that guys developing controllers are just too lazy. They are
pushing the problems with their bad models to us, pure programmers! (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de