Re: emc on microway alpha pc?

[Jon Elson <jmelson-at-artsci.wustl.edu>]

stratton-at-mdc.net wrote:

> The ISA bus may well be a bottleneck for many things in today's
> computers, but motion control I/O is not one of them.  No one runs a
> parallel port anywhere close the 8mhz or so limit of the 8bit ISA bus.

Perhaps not for running step & direction stepper drivers, but for running
the motion control boards I'm designing for the parallel port, it IS a
bottleneck.  Using an on-the-motherboard ECP port, I get about 600 K
bytes / second (1.6 uS per transfer), without using the special burst I/O
instructions on the x86 architecture.  This is on a 100 MHz Pentium.
I get about 20 uS per byte with an ISA SPP card, although this
requires the software to do the EPP handshaking, so it is not a
fair comparison.  Since I have to read, and write, more than a dozen
bytes each, every servo cycle, the overhead becomes a concern,
at least.

Jon