NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/gnu/emacs/help/3714

Text File | 1992-08-12 | 3.4 KB | 69 lines

Newsgroups: gnu.emacs.help
Path: sparky!uunet!pipex!demon!edscom.demon.co.uk!kevin
From: [e-mail] (Kevin Broadey)
Subject: Re: C-s problems
In-Reply-To: [e-mail]'s message of 12 Aug 92 14:16:57 GMT
Message-ID: <[e-mail]>
Sender: [e-mail] (Kevin Broadey)
Organization: EDS-Scicon, Milton Keynes, UK
References: <[e-mail]>
    <[e-mail]>
    <[e-mail]>
Distribution: gnu.emacs.help
Date: Thu, 13 Aug 1992 09:11:27 GMT
Lines: 53

In article <[e-mail]> [e-mail] (T. Scott Thompson) writes:

   This doesn't sound right to me.  More precisely, it is incomplete.
   Your explanation essentially states that the terminal sends C-s (XOFF)
   to the host when you press C-s at the keyboard.  This is undoubtably
   correct, but is probably not the source of the problem.  After all,
   sending out C-s is exactly what we want the terminal to do!

   I do not know the specifics of the DEC-VT220, but I suspect that the
   various "XOFF" commands mentioned control how the terminal responds to
   data arriving too fast from the host.  That is, when you set "XOFF at
   64" this probably means "OK terminal, if your input buffer has less
   than 64 free bytes you should _automatically_ send out a C-s to tell
   the host to stop sending."

   But this is a digression.  The real problem is that when the host
   _receives_ the C-s it is interpretting it as the message "stop sending
   characters" instead of passing it along to emacs.  That is, the
   flowcontrol processing _at_the_recieving_end_ prevents emacs from ever
   seeing the C-s.  It also causes the host to temporarily stop echoing
   characters back to the terminal, which is why your terminal _appears_
   to be locked.  (It isn't really locked in all likelihood.)

   Ideally emacs will turn off XON/XOFF flowcontrol at the host
   automatically when it is in command. However there are situations when
   emacs cannot do the job.  For example, I usually connect to my host
   through a network terminal server that does its own flowcontrol
   processing.  Unless I turn that off (manually) when I make the
   connection, the host never even receives the C-s, since it is
   intercepted and processed by the terminal server.

   Bottom line: The problem _is_ flow control.  The solution is likely to
   be more complicated than simply turning off XON/XOFF flowcontrol at
   the terminal end.


Okay, you got me!  I forgot to mention the terminal concentrator being a
possible source of flow control problems.  I remember seeing that in one of the
PROBLEMS files in the emacs distribution.

As to my description of how a DEC-VT220 works, this is *exactly* what happens
(unless someone's rebadged the terminal I'm sitting in front of!).  If you have
"XOFF at ..." set, "C-s" freezes the terminal *immediately*, and it only
forwards "C-s" to the host when the specified buffer (64 or 128) fills up.

But before anyone else flings their own pet theory into the fray, perhaps we
should wait for Ted Pedersen to post his equipment configuration so we can
*all* make a more *informed* diagnosis.
--
Kevin Broadey, EDS-Scicon
Mail:    Wavendon Tower, Wavendon, Milton Keynes, MK17 8LX, England
E-mail: [e-mail]
Phone:    [phone] or [phone] ext 4198