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From: smith@COS.COM (Steve Smith)
Newsgroups: comp.arch
Subject: Re: paging in the terminal driver
Message-ID: <531@cos.COM>
Date: Fri, 6-Nov-87 11:21:39 EST
Article-I.D.: cos.531
Posted: Fri Nov  6 11:21:39 1987
Date-Received: Sun, 8-Nov-87 14:26:20 EST
References: <573@elxsi.UUCP> <682@its63b.ed.ac.uk> <796@quacky.UUCP> <1444@osiris.UUCP> <858@gumby.UUCP> <17321@mordor.s1.gov>
Reply-To: smith@cos.UUCP (Steve Smith)
Organization: Corporation for Open Systems, McLean, VA
Lines: 30
Keywords: output pagination
Summary: Watch it!!


One of the nastiest kludges that I have ever been involved with was
caused by a "smart" terminal driver that did all kinds of tricks.  The
system had a PDP 11/23 running RT11 and an HP 2626A "smart" terminal.
The idea was to "draw" forms on the terminal in local mode and then dump
them to the computer as a block transfer.

Ideally, the computer would be running "PIP filename=TT:" (for you UNIX
types, "cat >filename").  Enter the "smart" terminal driver.  It uses
all sorts of control characters for its own purposes.  Naturally, there
was an overlap with the characters that the terminal used.  The killer
was control-O, which is "discard output" on RT11 and "turn off graphics
character set" on the 2626A.  Needless to say, there was no way of
turning off the "discard" function, because it was wired into the
driver.

What should have been a one liner turned into about 2.5 pages of
spectacularly obscure PASCAL, using system calls that even the RT11
gurus had never seen before...

The moral is obvious.  Drivers, as part of the operating system, should
be as clean, simple and general purpose as possible.  If you want
something fancy, do it as an add-on THAT CAN BE REMOVED.

I've never had any heartburn appending "| more" to a command.
-- 
                           __
 -- Steve          /      /  \      /         "Truth is stranger than
S. G. Smith      I \ O    |  _    O \ I        fiction because fiction
smith@cos.com      /      \__/      /          has to make sense."