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Path: utzoo!watmath!clyde!rutgers!husc6!ddl
From: ddl@husc6.UUCP
Newsgroups: comp.os.minix
Subject: Re: use of bios routines in the minix kernal, why not?
Message-ID: <1216@husc6.UUCP>
Date: Thu, 12-Feb-87 18:25:51 EST
Article-I.D.: husc6.1216
Posted: Thu Feb 12 18:25:51 1987
Date-Received: Fri, 13-Feb-87 21:15:50 EST
References: <172@axis.UUCP> <1192@husc6.UUCP> <431@percival.UUCP>
Distribution: world
Organization: Harvard University, Cambridge MA
Lines: 39
Keywords: interupt poll

In article <431@percival.UUCP>, nerd@percival.UUCP (Michael Galassi) writes:
> Nope, sorry, the combination gives you a polled keyboard.  As things stand
> now, if you call the bios to do a read it will sit there and *poll* the FIFO
> status until it finds that a key has been hit, then it returns with the
> key's value.  Alternately your code could check the FIFO status and loop until
> something showed up (duplicating the bios' code), you would still be polling
> the keyboard's queue.  While it may be different in words the result is stil
> that the cpu is doing nothing usefull while waiting for the slowest link in
> the computing machine (the live-ware).

	Let me try again, real slow.  First intercept INT 9.  When it
occurs, call the BIOS INT 9 handler.  The BIOS will do all the messy
key mapping, tell the keyboard that it read the key, send an eoi to
the interrupt controller, etc.  Now, while STILL AT INTERRUPT TIME, use
the BIOS poll function to read a key.  If there was something there, hand
it to the tty driver and do a destructive read to remove it from the BIOS
fifo.  Sometimes there will be nothing to read (key-up event).  The idea
is to use the INT 9 event as a cue to read the keyboard.
	This is not a polled keyboard.  This is an interrupt-driven keyboard.
This works.  This is how I read the IBM PC keyboard on my multi-tasking
operating system.  If you want a demonstration then you can either come
visit me or buy a copy.
	Not using the BIOS because you think it is ugly is a matter of
taste.  This is presumably why MINIX does not use it.  Not using the
BIOS because you think it can't work is a matter of misunderstanding.
Could we please end this silly discussion?

> power the machine up, it is inherently in an unstable (unusable) state,
> that is designed in to ms/pc-dos

	Joke?

> two people have seen the light, we're on a roll now.

	Dark destroys the light...


					Dan Lanciani
					ddl@harvard.*