How to delay until a next increment of time occurs ?

[Rob Gaddi]

On 11/14/19 12:34 PM, R.Wieser wrote:
> Dennis,
> 
>> The R-Pi has never, to my knowledge, been billed as suitable
>> for industrial/real-time/process-control...
> 
> I have not read those specs to be honest.   But for some reason I assumed
> that a 1.4 GHz machine should easily be able to generate a 1.6 KHz signal,
> even using Python.   I was wrong. It can, but just barily and not without
> jitter and hickups.  Lesson learned.
> 
> Regards,
> Rudy Wieser
> 

The machine itself would be fine.  But between Python and Linux (probably the 
bigger culprit), there are lots of things that aren't interested in your 
deterministicity.

Just run it bare-metal; I'm sure that's straightforward on an rPi and has no 
gotchas or complications that would lead to days/weeks of frustration.

On an actually practical note; ever since they started baking the quasi-realtime 
stuff into the Linux kernel, you've been able to use the whole 
sched_setscheduler(2) family of calls (from C) to set a process's real-time 
priority.  That might get things good enough to do the job, though how one gets 
there from Python I couldn't tell you.  Naïvely I'd say to just use ctypes to 
wrap those calls, but that's some low-level stuff to be getting into from a very 
high-level language.  Might work?

-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.