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From: lcc.jbrown@UCLA-LOCUS.ARPA (Jordan Brown)
Newsgroups: net.unix-wizards
Subject: rts/cts on 3b2 tty ports (flow control)
Message-ID: <10801@brl-tgr.ARPA>
Date: Fri, 17-May-85 21:41:10 EDT
Article-I.D.: brl-tgr.10801
Posted: Fri May 17 21:41:10 1985
Date-Received: Sun, 19-May-85 05:52:50 EDT
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>From: phil@amdcad.UUCP (Phil Ngai)
>> [ wants to use RTS/CTS for bidirectional flow control ]
>That's gross. You should use XON/XOFF for flow control.
No, _that_ is gross.  Quite a number of things require a full 8-bit data
path to the terminal (uucp, kermit in some modes, emacs, umodem, graphics
devices), and having an intermediary eat two of the characters is terrible.

Wire-based handshaking several advantages - it can be implemented
in the hardware and is completely transparent.  On the other hand, it
doesn't propagate through networks and modems.

What would be nice, in these days of intelligent terminals and reasonable
tty drivers, would be for somebody to develop a transparent flow-control
mechanism based on characters, so that it would pass through nets and modems
but be added and stripped by low-level software (maybe even hardware??)
so that an 8-bit data path is maintained.

A simple example would be, say, to define that ^Vx means that x is not
special.  Thus, when told to send ^S, the tty driver (or whatever)
would magically turn it into ^V^S, and the other driver (at the other end)
would strip the ^V.  (Of course, ^V^V is used to send ^V.)  Another, and
perhaps better, method would be to define a single line-control character
(say, ^\), and ^\x is a command of some form.  ^\^\ should mean ^\,
^\^S mean stop, and so on.

NOTE:  I don't particularily care what scheme is chosen, but people should
agree on _one_ scheme so we don't have six incompatible ones next year.

Whew, that was more than I meant to write, but it's a subject I'd like to
see addressed.  (I would like to use emacs, but my terminal needs ^S^Q so
I can't reasonably do so.)