Re: [CAD_CAM_EDM_DRO] Re: USB on Linux

Matt Shaver wrote:

> Ray wrote
>
> > I had some discussion with Matt Shaver about this recently and he thinks
> > that you can consistently get 1 microsecond if you don't try to do
> > anything else with it. Problem is that you want a bunch of connections
> > running around the machine or process.
>
> Holy orders of magnitude Ray! That's 1 MILLISECOND not 1 microsecond...
>
> As I understand it, with USB you can send and recieve data with each
> device address once every millisecond. If each encoder, DAC, I/O
> controller, etc. had its own address you could go through them at 1kHz.
> Another trick (told to me by Steve Stallings) would be to give each
> device multiple addresses so that you could access it multiple times
> during each 1 mS "frame".
>
> I still like the parallel port better for now though...

A LOT simpler, no foreign protocol to adhere to, or be limited by, no
problems with resolving who gets to talk now, minimal overhead....
Yes, the parallel port really is great with the EPP mode. I can do the
entire transaction for a 3-axis control in 24 CPU instructions! (This is
just the final part of reading the encoder counts and sending the
DAC outputs, and the digital I/O. But, that is MINIMAL overhead,
for sure! I have no idea what the USB overhead on the CPU is, but
it has to be WAY more than that!)

Jon