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000046_news@newsmaster….columbia.edu _Sat Oct 4 12:17:12 1997.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc,comp.os.linux.misc
Subject: Re: 2 queries
Date: 4 Oct 1997 16:17:10 GMT
Organization: Columbia University
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In article <34325162.42877E5C@rss.rockwell.com>,
Ian Diddams <ian.diddams@rss.rockwell.com> wrote:
: 1) Is there an archive of comp.protocols.kermit.misc anywhere that you
: know of:
:
ftp://kermit.columbia.edu/kermit/newsgroup/misc.*
: 2) I can use kermit fine on my linux box (usr robotics 14400 internal)
: but after dialling, connecting, doing, exiting.... I return to kermit,
: but on exiting I get a message regarding "serial connections may still
: be open".
: I can't find a command to "clear" this staus, but if I exit anyway, next
: time I try to use kermit, it "hangs" trying to set line /dev/ttyS1;
: there's nothing obvious in /var/lock.
: What am I doing wrong?
:
Ian and I worked this one out over the past few days while his posting was
in transit. We now have the following entries from Ian and others in the
working copy of the C-Kermit for UNIX "beware file" (ckuker.bwr):
"set line /dev/modem" or "set line /dev/ttyS2", etc, results in an error,
"/dev/modem is not a tty". Cause unknown, but obviously a driver issue, not a
Kermit one (Kermit uses "isatty()" to check that the device is a tty, so it
knows it will be able to issue all the tty-related ioctl's on it, like setting
the speed & flow control). Try a different name (i.e. driver) for the same
port, e.g. "set line /dev/cua2" or whatever.
"set modem type xxx" (where xxx is the name of a modem) followed by
"set line /dev/modem" or "set line /dev/ttyS2", etc, hangs (but can be
interrupted with Ctrl-C). Experimentation shows that if the modem is
configured to always assert carrier (&C0) the same command does not hang.
Again, a driver issue. Use /dev/cua2 (or whatever) instead.
More on the ttyS0 vs cua0 issue (quoting from a user, October 1997):
Platform: Intel 486 PC, Caldera Open Linux (Base), USR Robotics 14400
internal modem.
Problem: When using C-Kermit with a ttyS? device, the modem works fine the
first time a modem connection is attempted. Upon exiting kermit, the message:
"A serial connection might still be active on /dev/cua1. OK to exit?" is
displayed.
Answering "yes" at this point seems to hang the line up, such that the next
time C-Kermit is run on that device, it will not open the line - C-Kermit just
sits there until the user breaks (control-C). Nothing within C-Kermit appears
to rectify this situation - the same question is asked with the same
consequences whatever attempts are made to "clear" the line.
The workstation must then be rebooted.
Fix: Although the Linux implementation may not necessarily indicate that it is
available, the cua? device is available as an alternative to the ttyS?; e.g.
/dev/cua0 works as well as /dev/ttyS0.
Use this /dev/cua? device instead of the ttyS? one, and although the same
message might be displayed on exit, the consequences do not occur; i.e. the
line is available again next time C-Kermit is used ... and without rebooting
the workstation.
Reasons: ???? See Linux documentation with your distribution if there is any,
otherwise Linux documentation is available on the WWW.
(end quote)
from /usr/doc/faq/howto/Serial-HOWTO
12.4. What's The Real Difference Between The /dev/cuaN And /dev/ttySN
Devices?
The only difference is the way that the devices are opened. The
dialin devices /dev/ttySN are opened in blocking mode, until CD is
asserted (ie someone connects). So, when someone wants to use the
/dev/cuaN device, there is no conflict with a program watching the
/dev/ttySN device (unless someone is connected of course).
The multiple /dev entries, allow operation of the same physical device
with different operating characteristics. It also allows standard
getty programs to coexist with any other serial program, without the
getty being retrofitted with locking of some sort. It's especially
useful since standard Unix kernel file locking, and UUCP locking are
both advisory and not mandatory.
The best advice about using /dev/ttySx in C-Kermit seems to be, like the
doctor says, "if it hurts, don't do it".
If any Linux experts would care to shed further light on this, please do!
- Frank