SVR4 (i386) serial port setup

[Tony Becker]

>From article <1991May8.194639.28749 at ux1.cso.uiuc.edu>, by mandel at ux1.cso.uiuc.edu (Hector Mandel):
> urban at cbnewsl.att.com (john.urban) writes:
> 
>>>saying "CAN'T ACCESS DEVICE". 
> 
>>Did this exact hardware configuration work on AT&T SVR3.2.2 ?

 probably.

> 
> mandel at ux1.cso.uiuc.edu

Ok. Here's my two cents.

1) ATT requires DSR present to 'open' the port. Force it high.
   This is true for SVR4 as well as the 3B2. Its a feature.

2) Now you have DTR & RTS out, CTS & CD in (and TD/RD).

   a) for a modem connection (Dial in), the getty will respond if,
   and only if CD is high; so your modem MUST be set to auto answer.
   You can't force CD high, or the device driver can't tell getty
   that there is an incoming call.

   b) for a modem connecting (Dial out), the device driver will allow
   you to write to the modem when DTR goes high (it will on open),
   but you can't read from the modem until CD goes high, which it won't
   until AFTER you dial, which you can't because you can't read from
   the modem.... (catch 22). So for dial out, you must force CD in.

   This makes ports mutually exclusive to Dial In/Out.

   This is true on the 3B2. (It's STILL a feature).

3) What I Do...

   Configure the Modem/Port for a dial out case and use ringback, or
   some other inteligent program that looks for the modem to RING.
   When this happens, you can spawn a getty to the incoming call.
   Out going calls just require the ringback daemon to stay out of the
   way. This configuration also has the added advantage of locking
   the Port - Modem speed (to 9600bps) allowing a greater getty pick up
   for various incoming modem rates.


The address out of rb.c is:

   Paul Traina (pst at anise.acc.com)
   Jon Zeeff (umix!b-tech!zeeff)

Either are free to contact me for any other details, as I have modified
their source for a Courier HST.
-- 
tony ,....