Xref: utzoo comp.dcom.modems:2819 comp.sys.att:4664
Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!wasatch!utah-gr!uplherc!sp7040!obie!wsccs!terry
From: terry@wsccs.UUCP (Every system needs one)
Newsgroups: comp.dcom.modems,comp.sys.att
Subject: Re: MORE 6386 UUCP WOES ...
Keywords: cu, Hayes Modem
Message-ID: <756@wsccs.UUCP>
Date: 29 Oct 88 23:57:30 GMT
References: <319@argon.UUCP> <2096@cuuxb.ATT.COM> <727@wsccs.UUCP> <16509@onfcanim.UUCP>
Lines: 50

In article <16509@onfcanim.UUCP>, dave@onfcanim.UUCP (Dave Martindale) writes:
> In article <727@wsccs.UUCP> terry@wsccs.UUCP (Every system needs one) writes:
> >
> >The general UNIX implementation of modem-control devices is that of setting
> >either bit 6 or 7 of the minor device number.  To find out for sure
> >which should be used on your system, check sio(7) in your manual.  In
> >general, if the minor device is greater than 64, it's a modem control
> >device.
> 
> I don't know about system V UNIXes, but on all of the older UNIX versions
> plus the BSD variants, the default device supported modem control - it's
> the only sane way to handle dialins.

Unfortunately this is not true.  BSD, particular on Sun systems, requires a
kernel reconfiguration to properly handle modem control on a port.  The port
is useless without proper modem signals unless configured back.  I have manual
pages for a Sun 3 and references in sio(7) in the Sun manual and management
guides.  I also have specific release notes dealing with this.

> Sometimes an upper bit in the minor devices was used to add a "nowait"
> device, that allowed you to talk to the modem without waiting for
> Carrier Detect, but this is not always present.

The nowait feature is built into the O_NDELAY open flag; using the minor device
bit 6 or 7 for this behaviour only ocassionally would be wrong.

> Maybe it is just Xenix that gives you no modem control by default?
> This is pretty brain-damaged behaviour.

All system V systems and all Berk systems I am familair with (Digital, Sun,
Icon, etc) work this way.

A modem control device is one where an open hangs until modem control signals
are asserted.  A non-modem control device is one where the open completes
without those signals being asserted.

Any installation which is using a stright 3-wire cable to their terminals is
using a non-modem control port or they have hacked the computer end of the
cable to force DCD and possibly CTS/RTS if it is a system V system with
AT&T's 3B2-style drivers.

Please examine tty.c for the comment "partial open hack" in your UNIX source.
The 20 or so lines on either side will be enlightening.


| Terry Lambert           UUCP: ...{ decvax, uunet } ...utah-cs!century!terry |
| @ Century Software        OR: ...utah-cs!uplherc!sp7040!obie!wsccs!terry    |
| SLC, Utah                                                                   |
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