Xref: utzoo comp.sys.att:8204 unix-pc.general:4254
Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!mailrus!rutgers!att!dptg!mtunb!jcm
From: jcm@mtunb.ATT.COM (John McMillan)
Newsgroups: comp.sys.att,unix-pc.general
Subject: Re: 7300 and 9600 baud modems (VT220 suggestion, and question)
Summary: Overrun exists!
Message-ID: <1711@mtunb.ATT.COM>
Date: 4 Dec 89 22:08:00 GMT
References: <3311@convex.UUCP> <24425@cup.portal.com> <581@limbic.UUCP> <1709@mtunb.ATT.COM> <1846@neoucom.UUCP>
Reply-To: jcm@mtunb.UUCP (John McMillan)
Organization: AT&T ISL Middletown NJ USA
Lines: 38

In article <1846@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes:
>
>I don't have any problems with my Trailblzer on my 3b1.  I've been
>using a TB since 11/1987.  I started with one of the old version
>3.1 TBs and then switched to the white-cased TB+.

	I'm totally 8-) for you!

>The problem of over-runs happens when you use in-band signaling
>with xon/xoff.

	There are three principle overruns:
		- RS-232 Chip overruns
		- 'seriobuf' overruns
		- C-list overruns

	The former occur when the duration of "high-level" interrupts
	exceeds ~2 * receive-time for a single character.  This
	*DOES* occur, and it's easy to produce using a terminal
	off any port to CU to another system at 9600 baud.
	Just CAT a file and watch the bytes get lost.  Then do
	a "~%take" into a file: all characters will be received,
	indicating it was the load associated with the DISPLAY of the
	characters to the terminal that induced the chip-overrun.

	'seriobuf' overflow occurs when sustained low-level interrupts
	prevent the unloading of this temporary buffer into the
	C-list mechanism.

	C-list overruns occur when the CPU-usage is so high that
	user programs cannot read the data as fast as it is
	arriving and the C-list use-limits are being circumvented.
	Flow-Control (H/W or S/W) can deal with this, and only with this.

The preceding comments are probably flawed -- I've other things to
deal with -- but they're pretty accurate!-)

john mcmillan -- att!mtunb!jcm	-- tic-toc-tic-toc...


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