...
HOWEVER, the Gill at s12 is bad. When I rserial to it, I get binary gibberish. I have now checked (using minicom) that this isn't a baud rate issue. I've also verified that "tp4" shows the same settings (120ohm termination, normal slew) as for s13, which is working. (I also played with these settings and didn't noticably change the signal.) I conclude that this is not a problem with DSM settings, but a cabling issue or something in the Gill itself.
...