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From: manes@dasys1.UUCP
Newsgroups: comp.unix.wizards,comp.unix.questions
Subject: Microport Unix V/AT and 9600 baud
Message-ID: <1198@dasys1.UUCP>
Date: Sat, 5-Sep-87 02:56:39 EDT
Article-I.D.: dasys1.1198
Posted: Sat Sep  5 02:56:39 1987
Date-Received: Sun, 6-Sep-87 20:45:43 EDT
Organization: The Big Electric Cat, NYC, NY
Lines: 51
Keywords: Microport Unix
Xref: utgpu comp.unix.wizards:3829 comp.unix.questions:3519

I've heard rumblings for some time that Microport has some troubles
supporting 9600 baud, the usual complaint being that it loses characters.
I've been porting Magpie (my BBS program) to Unix from MSDOS and have
been testing it with a 9600 baud terminal and null modem line to tty0
(ttyM0).  What I've learned from several months of this is that while
Microport can handle 9600 baud under light i/o with little problem,
sustained output from a 9600 baud terminal, even the relatively short
blocks of Forsberg's YMODEM, is severely corrupted.  At worst, it
can crash Unix and leave you staring at the dreaded "double panic:"
error that means pulling the plug and restarting.

To test this phenomenon, try running a 'cat > filename' from a 9600
baud computer (not dumb terminal) and dumping a fairly large text file
to Unix.  I spent an hour trying to transfer a large (1 meg) file from
an MSDOS AT running Procomm to Unix.  After a dozen aborts, and three
complete crashes, I finally transferred the file successfully with
Xmodem (Forsberg's 'rz').

This week, I've been writing Magpie's protocol up/download module.  I
had never gotten Ymodem to run reliably at 9600 baud on Microport and
so figured the available PD file transfer utils with Ymodem must be
brain-dead, at least for V/AT.  Xmodem worked fine.  So did my Xmodem.
I tested it about two dozen times, simulating line noise and sync errors
by sending the receive process messages during file transfer.  No problem.
Then I increased block size to 1024 (for Ymodem).  Curses!... I couldn't
get even a single block to transfer successfully.  I spent a good 48
hours tearing my code apart, retesting (and rebooting) and couldn't lick
the problem.  Then I downshifted the remote terminal to 2400 baud and,
voila, Ymodem worked!  So I added some logging tags to the program to see
what the hell was going on with Unix at 9600 baud and found that entire
blocks of the transferred text were being scrambled when read by the
receiver.  Some blocks were missing; some were inverted.  This leads me
to believe that the internal buffering is somehow overflowing or
otherwise confusing Unix.

o	I know the remote AT works fine at 9600 baud.  I routinely
	null-modem large files between it and an XT.

o	The Unix box is a 10 mHz AT running a pair of 16450 UARTs.
	Microport version is 2.2.U.

o	Through the >same< code block, Xmodem works fine.  Increasing
	the sending block to 1024 bytes generates the problem.

Have any Microport users experienced similar problems?

+---------------------------------------------------------------------------+
|  Steve Manes (NYC)	  !ihnp4!{pur-ee|iuvax}!bsu-cs!zoo-hq!magpie!manes  |
|  Roxy Recorders, Inc. (multitrack recording)				    |
|  Magpie BBS Develop. (UNIX/MSDOS 212-420-0527)			    |
+---------------------------------------------------------------------------+