Jeff Epler wrote:
>
> The specific problem you're experiencing is probably an incompatiblity
> between the EPP protocol implementation in pluto-p and your PC.
Well, I'm not so sure. I don't know the Pluto at all, but I gather it
has encoder counters
on the FPGA. If these encoder counters are accumulators, then I don't
believe EPP
mis-communication is the problem. It would cause WILD jumps in position
from sample
to sample that DO return. What we see in the Halscope trace is erratic,
but SMALL incremental changes
in position that DON'T return. Now, if the Pluto encoder system reports
deltas every servo period, your
suggestion makes MUCH more sense. What I mean by deltas is that every
servo period
the change in position is reported and the counter is zeroed. The way
the Pico boards
do the encoder counter is there is a 24-bit signed counter in the FPGA,
and the absolute
position is reported every servo period. The driver handles overflows
to extend range
beyond 16 million counts.
My take on the trace is that it is motor drive noise getting into the
encoder inputs.
> This is one example of the superiority of the Mesa and Pico EPP
> products--they are designed with appropriate termination on the EPP bus,
> while the Pluto is not. This means that certain problems on the Pluto
> board may be due to the board design and simply not fixable in software.
>
Early versions of the PPMC and Universal {Stepper | PWM } Controllers
did not have
termination. It was only a little problem before PCI parallel port
boards came out.
Rev 2.1 (I think) and later boards had the terminators hacked in by hand
at first when
I discovered this problem.
But, with the non-resetting position accumulators, comm errors would
show wild
jumps in position and then return to the correct value next servo period.
Jon
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