Re: [CAD_CAM_EDM_DRO] re: Re: Re: Black box ??

There are many ways to make this experiement always pass and many ways to
make it always fail from the programmer's prospective depending on his
motives.

But, it's not a very valid test as described.

We all know how terrible CNC software is that experiences pauses during
motion.

One way to resolve this is to take the OS out of the equation as often as
possible.

If you have a bank of ram to write the step data or motion equations to,
then have an external controller to process this data, the OS of the host
system doens't get the chance to muck with the throughput.

USB is certainly dependable enough to parse out this data. It is a fairly
trivial task to program a USB microcontroller to handle emergency stop,
limit switches and other safety mechanisms to allow a USB control to be a
safe control even if the host computer crashes.

So the question is no longer, can USB do a point to point transfer at high
speed and not create a pause between transfers, the question is now, can USB
transfer a block of data often enough that the bit bucket doesn't run dry in
the external ram.

The answer to this is it's very easy to do this and USB is more than up to
the task. If you don't believe it is, just go get any USB device that
transfers digital video. That will let you see but a small portion of USB's
throughput.

You might not be able to find a USB 2.0 video device yet. USB 2.0 is MUCH
faster than USB 1.0.

Even on real time in circuit emulators for processors that run a hundreds of
megahertz clock frequencies, the emulator host doesn't stay synced up with
the bondout chip all the time. They sync up when necessary. The same can be
done for a CNC controller. Does it really matter if the graphic toolpath
picture is a few microseconds behind real time? Does it really matter if
during a rapid the axis readouts are a few ten thousands of an inch behind?
No, but what does matter is the motion is continuous without pauses and
critical events are handled properly.

later,
Larry E.

> How about an experiment to find out if USB is up to the task?
>
> Connect two computers with USB, send chunks to data from one to the other,
> regularly timed.
>
> Put timers on the receiving computer.
>
> If there are long periods when nothing is being received, then it looks

like

> USB might not work.
>
> Carry the experiment out over a long period of time, hours, perhaps days,

to

> see if you can catch the computer napping.
>
> Elliot
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