Re: [rtl] generate squares

[Paolo Mantegazza <mantegazza@aero.polimi.it>]

Hi,

> He is using it for a stepper motor where jitter is less important than
> pulse speed.

That's wishfull thinking. You are loosing steps for sure, so you cannot
use the step motor without a position sensor.

> > So while you can use that
> > rate without jamming your machine the square wave seen on a memory scope
> > will be just a thick black strip.
> 
> What do you mean by 'thick black strip'.  Change the 'time/div' knob to
> a  higher setting.  Check your other scope settings.  Use a scope with a
> rated frequency that is at least three times the desired sample rate
> (for analog scope).  What scope are you using.  At what settings?

I gave up the illusion of rates in that range long time ago. It is not a
matter of aliasing (3 times the sampling rate). You cannot obtain a
steady 120 Khz rate on PC motherboards, AS THEY ARE NOW. 

> > Hands on experience.
> 
> What code did you use for this experience?  You need to wait at least 17
> uSec in RTL before doing your tests to account for Linux ISA bus
> accesses over the PCI bus to stop (a large source of jitter).

Simple toggling of a digital IO, either parallel port of DAQ card. Many
makers, ISA and PCI, under RTAI, RTL and VxWorks. I can tell you that I
got more stable results on older 286s under DOS, clearly for lower
rates.

Ciao, Paolo.