Driving modems with tip...

[William L. Sebok]

>> As I understand using the same line for auto-answer and dialout can only
>> be done if you modify the tty driver to arbitrate between the two.
>> 				Jerry Aguirre @ Olivetti ATC
> 
>You do not have to modify tty driver to allow dial out and dial in on the 
>same line at least note on System and several pc versions of unix. All that
>needs to be done is for the program that uses the line to dial out must check
>to see if the line is in use and if not disable the getty from running on 
>the line.(On sys V this is done by changing to an init level which that
>oarticular line does not support.) Once this is done the program is free to use
>the line for dialout purposes. When the program is ready to terminate all that
>needs to be done is to re-enable the line and start the getty(sometimes this is
>done automatically).
> 				Larry Rodis @ Anasazi

It is also not necessary to modify the tty driver in 4.1 or 4.2 BSD to use the
same line for auto-answer and dialout (although modifying the driver is another
way to do it).  See my recent posting to net.sources to see how it is done.
The hardest thing is to do is enabling/disabling modem control on that line.
One wants modem control enabled on dialin so that the computer can sense when
the caller hangs up.  However unless modem control is disabled on dialout
the computer cannot (with present unix tty driver behavior) communicate with
the modem to cause it to dial the desired number.
-- 
Bill Sebok			Princeton University, Astrophysics
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