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From: cetron@utah-cs.UUCP (Edward J Cetron)
Newsgroups: comp.unix.wizards,comp.bugs.4bsd
Subject: Re: lack of modem control on MVAX-II with DHV running 4.3bsd
Message-ID: <4568@utah-cs.UUCP>
Date: Sun, 17-May-87 16:19:09 EDT
Article-I.D.: utah-cs.4568
Posted: Sun May 17 16:19:09 1987
Date-Received: Mon, 18-May-87 03:57:23 EDT
References: <7597@orchid.UUCP>
Reply-To: cetron@utah-cs.UUCP (Edward J Cetron)
Organization: Center for Engineering Design, Univ of Utah
Lines: 22
Xref: mnetor comp.unix.wizards:2370 comp.bugs.4bsd:358


	I went through this once before on my microvax even though it was
running vms.... It seems that in the 'standard' configurations, the dhv will
simply pass the state changes of the modem lines to the kernel (vms or unix) 
and not actually do anything itself. These changes can be polled for or can
generate an interrupt (from memory so I can't remember if the interrupt info
is coded or you have to poll the status bits).  Therefore, it is the KERNEL
that determines ALL modem handling (ok, so it is the driver no the kernel per
se...)

	In vms, the problem is that if you don't sequence any of the modem 
lines, the line will STILL work just fine but won't sequence any of ITS modem
lines. if you sequence any of the input modem lines incorrectly, then it will
lower dtr and start over...basically lousy control.

	In unix, I recall that the config files require you to set the flags
for each interface which (among other things) determine whether or not to do
modem control.  I suggest checking these first. Then read the driver code, it
may be messed up, or (like vms) require a very specific sequence for modem 
control.

-ed