> >> ... It looks like it might
> >> be easier with the uspace / rt-preempt kernel than with
> >> rtai.  It would reduce latency/jitter to ns levels.

If you build the system so that within servo period is OK things will get a lot 
easier and will fit with ordinary theory fo real time scheduling, dead time 
equal to period.

> Yes, actually, it WOULD.  All the Pico Systems motion 
> control boards can latch the position when the internal 
> timer ticks. ...

This is the way to do it.

> ...
> The master board sends the latch command on the parallel 
> port bus to other boards on the bus, as well as the 
> computer.  The computer would have the luxury of responding 
> before the next timer tick, nominally 1 ms.

This is a good way to get it synchronized a hardware 1kHz signal and the full 
1ms period left for software jitter software.

> As long as the computer never took more than the timer 
> period to complete its work, it would never cause ANY 
> latency at all!  The computer's updated velocity info would 
> not become effective until the next timer tick.

Then you use EDF or rate-monotonic scheduling it will make a perfect fit with 
the theory.

> Jon

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