Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!ames!ptsfa!ihnp4!ihwpt!warren
From: warren@ihwpt.ATT.COM (warren montgomery)
Newsgroups: comp.emacs
Subject: How we could have made flow control livable
Message-ID: <1759@ihwpt.ATT.COM>
Date: Mon, 22-Jun-87 10:03:37 EDT
Article-I.D.: ihwpt.1759
Posted: Mon Jun 22 10:03:37 1987
Date-Received: Thu, 25-Jun-87 05:35:48 EDT
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 34

I am not a fan of ^S/^Q, but flow control is a necessary evil for
some applications of terminals.  First, for all of those arguing
about whether flow control can be avoided when scrolling through a
megabyte file, realize that there are many ways to use a terminal. 
If you really want to watch a megabyte flash before your eyes or
have it spew onto your 10cps printer, you can't avoid flow control. 
If, however, you just want to re-paint a screen, like emacs and most
other applications do, the number of characters that the terminal
needs to buffer to avoid flow control is bounded by the number of
characters that fit on the screen (plus a bit for type ahead
situations).  This is what I think terminal manufacturers have
little excuse for not providing for.  The terminal should be able to
keep up with the line speed for long enough that a page can be
blasted out without flow control.

The place ^S/^Q really gets me, though, is on inter-machine links
(cu, rlogin, dkcu, etc.)  All of these on my system at least either
need ^S/^Q to function, or are broken in some way so that ^S/^Q is
permanently stuck on.  The unix TTY driver could have been written
in a way to make this all much easier, if it had allowed ^S and ^Q
to be escaped by preceeding them with backslash.  Then, over an
inter-machine link, if you turn off flow control locally, it passes
your ^S/^Q's through with backslashes in front and they go straight
to your remote emacs, while still allowing the two machines to use
^S/^Q internally.  (yes, you have to synchronize input and output to
the point where the receive half doesn't generate a ^S after a
backslash, but this isn't tough).  The backslash escape would also
allow emacsers to type these things from a terminal that needs ^S/^Q
if they really want to, provided that they are a bit careful about
typing backslashes during output.

-- 

Warren Montgomery,  ihesa!warren