How do you exorcise a haunted TNC?

[Murray_RJ@cc.curtin.edu.au]

   If I hadn't actually seen this one, I wouldn't have believed it. It all
started when I got a copy of GRINOS v1.8b, compiled it with my favourite
options, and installed it on my NOS machine. It didn't take long to
discover that there were two problems:

1. Most of the time NOS didn't actually do anything with packets coming in
   from the TNC, even though they showed up fine under trace. This, of
   course, is the famous axip bug, as several people have pointed out.
   Nothing really difficult about that.

2. The really weird one, though, was that I was getting wide-band noise
   into my receiver, at a high enough level to block incoming packets.
   Naturally, it was intermittent, but I was able to determine that it
   never came on when I ran the previous NOS version (1.7j). To confuse the
   issue further, it would usually become really strong if I stopped NOS
   and left the computer displaying the DOS prompt.

   I eventually established that it was coming from the TNC (turning the
computer off stopped it as well, for reasons that will become obvious). It
was somewhere around this time that I read some of the posts on DTR and
RTS and their changed settings with Phil's new code (and Gerard's as well).
I found that I could make the noise come and go by raising and lowering
DTR: with DTR on it was OK; with DTR off the noise would slowly come up.

   The TNC is a locally-produced TNC2 workalike (Z-80 CPU, SIO, that sort
of thing) with ROM version 1.1.7B; and apart from the radiated noise, it
worked fine with DTR off. I'm at a bit of a loss to explain the whole
think, but it seems that turning DTR on (with that "param" command) would
be a good thing, especially if you're getting unexplained noise levels.

P.S. Does anyone know why the 16550 FIFOs are disabled in 8250.h in the
PA0GRI code, but not in Phil's? (At least I assume they're disabled; I'm
not too familiar with the 16550, but FIFO Trigger Level and FIFO Size
are both set to 1, which I suppose disables them). I re-enabled them and it
all seems to work fine.

 .....Ron