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From: mdc@DELPHI.UUCP
Newsgroups: mod.computers.vax
Subject: XON XOFF and EMACS
Message-ID: <86.03.07.1418.637@delphi>
Date: Fri, 7-Mar-86 08:18:01 EST
Article-I.D.: delphi.86.03.07.1418.637
Posted: Fri Mar  7 08:18:01 1986
Date-Received: Wed, 12-Mar-86 06:31:22 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
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Approved: info-vax@sri-kl.arpa

About the XON XOFF / Emacs discussion i think 
that both parts are partly right and partly wrong .

Yes, emacs should be able to cope with the limitation of underling 
communication protocol.

BUT the XON XOFF protocol is really primitive:
thinking in term of layered levels of abstraction (for example ISO/OSI RM),
we may consider at least two interesting levels:
The user-application communication  level, and the 
terminal-computer communication level.
XON XOFF is primitive not because flow control in unuseful
but because it confuse the two levels of abstraction.
So a mechanism usually used to communicate with the application 
(i.e. ASCII characters) is used to control the communication
at the hardware level.

It is the same that having a special phone line 
where to close the communication you must say "Close!" instead
of press a button on the phone.

I think that a solution may be :

Add to XON XOFF a quote character  QUOTE (for example ^P).

So at the hardware level , 

^P    is a prefix character
^Q    means  stop sending data
^S    means  start sending data
^P^Q  means just the ascii character ^Q
^P^S  means just the ascii character ^S
^P^P  means just the ascii character ^P

The handling of XON XOFF QUOTE should be provided at the device
driver level and shold be completely transparent to the application.

If a manual control over the hardware level communication protocol
is needed there should be a not ascii key on the keyboard
that perform as a command to the terminal processor, just as
the key SET-UP do.

In this way you may have both hardware level flow control
and application level flow control without having problem 
with missing ASCII characters.


I agree, however, that XON XOFF is too widely used to 
ignore it or to change it now ...


Maurizio De Cecco
Delphi S.p.A.
Via della Vetraia, 11
55049 Viareggio
Italy
uucp: ...!mcvax!delphi!mdc

[Standard disclaimer]

[Standard  excuses for my bad english]