Dropping DTR?

[John E Van Deusen III]

Intelligent modems like the TB+ have a command mode, and you can write a
supervisor program that is respawned by init and deals with the modem at
the command level.  You can allow the modem to answer a call and, upon
establishing a connection, exec(2) getty(1M), and so on.  If you don't
want to answer the line, the program could sleep and periodically check
a status file, (this assumes that there exists some method to prevent
the modem from answering the line.  With the TB+ the S0 register is
assigned the value 0).

The supervisor program can also be written to support the resource
locking facilities of uucp.  The line can be available for login and
still used for outgoing calls.  Since the supervisor program doesn't
exec getty until a connection is made, you don't have the problem of
getty trying to assert login.  This also would work on serial ports
that don't support DTR.
--
John E Van Deusen III, PO Box 9283, Boise, ID  83707, (208) 343-1865

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