RE: USB, 1394, PCI, ISA, IDE ??

[Ray Henry <rehenry-at-up.net>]

Hardware folk

There is a fork in the hardware development path here. Both approaches get
i/o information into the real time part of emc so that we can do things
like asking an axis to follow a handwheel, pulse coder, or joystick. 

The developing TclTk iosh and tkio will soon make it possible for us to do
great things with this kind of PLC level machine control.  We may even be
able to write some tiny RT PLC SHMEM routines that we can launch with Tk
for time critical machine control tasks. 

One direction is being developed by Paul Corner.  This is a "homebrew"
replacement for the stg.  This one looks real good to me.  This has
immediate demand and is well underway. (the progress that we've made in the
last year is awesome!)

The second, less clearly defined, path is some kind of outboard device that
uses firewire or the parallel port to communicate with it.  This approach
has the advantage that it gets away from having a pile of wires from the
computer to the machine. It also allows us to set up multiple boards for
larger machines or groups of machines working together. Stuff like
pendants, tool hives, pallets, and robots.  

IMO we should keep the machine functions away from USB because of the many
existing general purpose devices available for it.  We can use USB to
connect between the computer, and the operator station using existing USB
components like keyboard, mouse, screen, floppy, and non-time critical I/O.
 With this approach we can put the computer into a coolant and swarf
resistant enclosure without the operator having to open that box regularly
and still have a managable number of wires running to the computer.

Perhaps those who know these things could compare the relative costs in
hardware to develop firewire vs parallel port.  We would also need some
sense of the software effort that it would take to make each fit into EMC
and the speed at which each would be expected to work.

Ray


At 12:45 AM 3/8/2000 -0500, Jon C wrote:
>
>Hi,
>I have been doing a little digging into IEEE 1394 (FireWire). It looks very
>good for what the list seems to want to do. Someone is already working on
>porting the drivers to rtLinux. His post comparing 1394 and USB is in the
>rtLinux mailing list archives. I have included the text below for
>information. FireWire interface chips are getting pretty cheap. Might be
>worth looking into: although it has scads of theoretical capacity. How about
>10KHz servo update rates on 10 axes!!!
>Regards
>John Craddock