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

[Mark H Johnson <mark_h_johnson@raytheon.com>]

Dmitry A. Kazakov wrote:

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

>>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! (:-))
> 
Nah. I just don't try to build brittle systems. Jitter is a fact of 
life. A 1 msec jitter on start time may be OK in one case but completely 
unacceptable in another. I know one system with a 50 usec window (every 
12.5 msec) to receive a message otherwise it will go into "safe mode" 
and take several minutes to recover. We don't even TRY to feed that data 
with a software interrupt handler - we set up the transfer in advance 
and use a hardware trigger to send the data.

In the case of missing a deadline, the action still should be 
application specific.

   --Mark