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From: jeff@fluke.UUCP (Jeff Stearns)
Newsgroups: net.emacs
Subject: Re: GNU EMACS 15.22 problem
Message-ID: <2290@vax4.fluke.UUCP>
Date: Mon, 6-May-85 16:52:23 EDT
Article-I.D.: vax4.2290
Posted: Mon May  6 16:52:23 1985
Date-Received: Wed, 8-May-85 05:40:44 EDT
References: <485@umd5.UUCP> <4160@mit-eddie.UUCP>
Reply-To: jeff@fluke.UUCP (Jeff Stearns)
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 30

In article <4160@mit-eddie.UUCP> smh@mit-eddie.UUCP (Steven M. Haflich) writes:
>I too have experienced the problem with GNU EMACS emitting garbage
>characters to the tty upon exit.  When using a VT100 emulator on a PC
>that reports ---BREAK-RECEIVED--- on framing errors, it bacame
>apparent that the problem is not extraneous well-formed characters,
>but some screwup resetting tty mode during exit, perhaps temporarily
>messing up speed or parity.  I may get around to checking the code
>one of these days.

Sounds like a problem I discovered when working with the line printer spoolers.

Some device filters do a series of ioctl's to change the tty modes while
driving the printer.  When finished, they switch 'em back - and a garbage
character can be introduced into the tty output queue.  It's an honest-to-god
character *fragment*.

Hang a good serial line analyzer on the line and you'll see the first few bits
of the character go by, then WHAM - it gets cut off in mid air.

I believe that it happens when the kernel is changing tty modes.  I suspect
that it may be sending a (premature) reset to the tty interface hardware while
the last character is in the midst of dribbling out the UART.

I found this problem on both 4.2BSD on a VAX, and on release 1.3 from Sun.
I now see hints that Sun may have fixed the problem in their latest release.
-- 
	Jeff Stearns       (206) 356-5064
	John Fluke Mfg. Co.
	P.O. Box C9090  Everett WA  98043  
	{uw-beaver,decvax!microsof,ucbvax!lbl-csam,allegra,ssc-vax}!fluke!jeff