Modem control woes

[Doug Alan]

We are having some problems with modem control on a uVAX-3200 running
4.3BSD with a DHQ11 serial line controller.  The problem is that when
the phone line gets hung up, the computer lowers DTR but often never
raises it again.  This causes the modem not to answer the phone line,
which makes the modem useless until someone goes and manually resets
or power-cycles the modem.  This usually causes DTR to be raised
again.

With a break-out box we have noticed that sometimes the modem will do
something weird, like flash DCD and DSR a couple of times while the
computer still has DTR lowered, and this definitely confuses the
computer and causes it to never recover.  However, even without this
weirdness, the computer often gets confused and never raises DTR again
when a phone line is hung up.

Someone here noticed that if the getty process on the wedged line is
killed, then the computer will raise DTR again, so now we have a shell
script that is run out of cron every ten minutes and kills the getty
on a modem line if no one is logged into it.  There must be a better
way, however.

The problem described above also occurs on a uVax-II.  It makes no
difference whether the DHQ11 is set to emulate a DHU or a DHV.  The
problem also occurs on a DHV11.  We are using the DHU driver that came
with BSD4.3, and the problem occurs on all of our modems, which are
from various manufacturers.  These modems worked fine when they were
on DZ ports in a VAX-11/750.

Does anyone know what is going on and how I might fix it?

|>oug /\lan
   (or nessus at athena.mit.edu
       mit-eddie!athena.mit.edu!nessus)