Re: STG2

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

Jan wrote:

> There is also a utility in the plat/linux/bin directory called stg2diag that
> captures the
> encoder data and shows it, when encoder impulses are received to fast it
> will generate a CR so you can closely examine.
> With this utility I saw that my encodersignal was flipping between 1 and
> env. 65000 and belief me or not tweaking the bios solved the problem.

Well, if the program only displays the lower 16 bits of the 24-bit encoder
counter in unsigned format, then it would be quite reasonable to see the count
flipping
between 65535 and 0, or even, say, between 65534 and 1.  This is because
the real counter is signed (24-bit) and when it detects a negative transition
from 0, it has to go to a negative number.  The 65535 is actually the unsigned
16-bit representation of a signed 16-bit value of -1 !  That is fairly normal,
and it is VERY common for high resolution encoders to practically always
be sitting right on the edge of a transition, so the count is flickering back
and forth one count.  If the servo amps are on, then a flicker over several
counts might be very reasonable to expect.

> Try to run the board on a different base-address?

VERY good suggestion!  A conflict on the I/O addresses is a VERY strong
possibility!  Especially, if the STG2 is like the original STG, it has TWO
separate, rather large banks of I/O addresses.  A conflict could easily
cause something like this.  (It would be likely to also mess up the other
device, but maybe you aren't using that other device.  Sound cards eat
up a huge number of I/O and interrupt addresses and DMA channels.

Jon