Re: USB on Linux

The 1 mS per USB frame is correct for the USB that
is currently available. This is only possible
for modes that transfer every frame, and these
modes are limited to small packets. These
packets are large enough for our purposes, but
"bulk" mode is used for printers and scanners
to move large amounts of data more efficiently,
but with uncertain time of delivery. There is
a faster USB 2 coming, but I have not yet had
my hands on it to see if it really helps in
real time situations.

I agree that USB is harder to use than a parallel
port, but it is possible. The significance of
this is changing however as we are fast evolving
into a world where most users have never seen
"plain" DOS. The time is coming when it is assumed
that it is the device must be intelligent, not the
user. I really do believe that in a couple of years
finding a new computer with a parallel port will be
difficult for the average user.

So what is the future? The current standoff seems
to be between Firewire (Apple/Sony primarily) and
USB (Intel/Microsoft primarily). USB excels for
keyboards, mice, modems, printers, etc. whereas
Firewire excels for hard disks and video. Currently
it makes sense for a good computer to have both.
USB 2 is an attempt to change that and it remains
to be seen if USB 2 will work as claimed and will
penetrate the market. It will truly be marketing
that decides, because as with the case of industrial
computers, unless it is intended for the masses we
will not be willing to pay the price demanded. All
of this is irrelevant when talking about surplus,
please consider my comments in that light.

Cheers,
Steve Stallings

--- In CAD_CAM_EDM_DRO@y..., Matt Shaver <mshaver@e...> 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...
>
> Matt