[Emc-users] Latency - was Re: Which video card/driver for LinuxCNC?

[Roland J. <rol...@gm...>]

On 20 February 2012 06:14, Jon Elson <el...@pi...> wrote:

> Dropout wrote:
> > A quick question, does latency matter for servo drives?
> >
> Yes, absolutely.  But, it is not as critical.  For software stepping,
> the base
> thread is typically around 20 us, and so a jitter of even 5 us is more than
> noticeable.  But, on a typical servo system (or a stepper with external
> step generating hardware) there is no base thread and the servo thread
> runs at 1000 us, so the effect of a 5us jitter is insignificant.  As long
> as
> the worst-case jitter never exceeds 20 us, servos should run flawlessly.
>
> Jon
>
>
So the norm is that a stepper system can run off the parallel port, but for
DC servo's, extra hardware is required to sample the encoders.

My question is; if one built a headless system(no video) and disabled
drivers wherever possible, would such a system be fast enough to run DC
servo's and read the encoders on the parallel port?

Regards
Roland