Unix-PC crashing during uucico

[Bill Mayhew]

We get random crashes on our 3b1, neoucom, which serves as our
gateway to the uucp domain.  Running the stock version 2, we had
more crashes than we get with the HDB system.  The bugs seem to
happen if you have more than one uucp running at a time, such as
ph1 and tty000 together.  The port driver seems to get confused
while handling the 7201 interrupts and leaves a boluxed address in
one of the 68010 registers.  Supposedly this problem was fixed in
3.51d (which it would appear is only available inside of AT&T at
this moment).  With HDB, you can set Maxuuxqts to 1, which it
seems, should prevent multiple uucicos from running.

None the less, we get an occasional crash every week or two.  That
isn't too awful, considering the 3b1 handles 2 or more megabytes of
news and mail on busy days.  If that news gets bottled up, it can
be a problem, so I built a hardware solution.  I looked through my
junk box and came up with a 6502, 6522, 2716, 6116, and a 16
character LCD display.  I put together a very small computer that
watches the tty000 port on the 3b1.  If my box doesn't see any
activity on the tty port for more than 70 minutes, it turns off a
solid state relay for 30 seconds to cut power to the 3b1, forcing a
reboot.  We set up Poll to make sure that uucico runs once an hour.
The 6502 program is only about 1K of assembly level code, and most
of that is for running the LCD display.  I also wrote in support
for input from an overtemp thermistor, but we've been too lazy to
disassemble the 3b1 to mount a termistor on the power supply.  I
experimented with measuring the temperature of the air coming out
of the fan grille, but variations in the room temperature were too
great to differentiate between fan failure and ambient variation.
I also ruled out using an air pressure sensor as too unrliable as
well.  On our 3b1, the air leaving the fan is only about 5 degrees
C above ambient.  I suppose one could take a differential
temperature measurement, but laziness kept me from getting that
fancy....


Bill