Getting Modems to work under Ultrix Version 1.2

[Stuart D. Gathman]

In article <107 at mit-prep.ARPA>, shanzer at mit-prep.ARPA (Mike Shanzer) writes:

> 	I have a question, I am trying to open a modem for writting under
> Ultrix V1.2, how ever when I try to do this the open hangs. DOes any
> one know why it does this and how I can fix it? 

The open is waiting for the modem to connect (i.e. for CD to turn on).
If this is a Hayes type auto-dial modem, you need to open it in a mode
which does not wait for 'CD'.  On some systems, this is a special device
file which has no modem control (this emulates older autodialers which
required two ports: one for dialing and one for communications).  On others,
(and this *should* work on all systems, but alas there are always bugs)
you should give the O_NDELAY parameter on your open.  This will ignore
the CD lead while you give dialing commands.  Ideally, another process
should be waiting on an open without O_NDELAY, i.e. fork() to do the
dialing.
-- 
Stuart D. Gathman	<..!seismo!{vrdxhq|dgis}!BMS-AT!stuart>