From mboxrd@z Thu Jan  1 00:00:00 1970
Message-Id: <200105210447.GAA29394@chuckle.iba.co.za>
From: lucio@proxima.alt.za
To: 9fans@cse.psu.edu
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Subject: [9fans] Floppy driver
Date: Mon, 21 May 2001 06:49:35 +0200
Topicbox-Message-UUID: a4141786-eac9-11e9-9e20-41e7f4b1d025

The following code:

print ("floppyrevive(%d): %lux - %lux\n", ++x, &fl, fl.d);
		/* reset controller and turn all motors off */
		splhi();
		fl.ncmd = 1;
		fl.cmd[0] = 0;
		outb(Pdor, 0);
		delay(10);
		outb(Pdor, Fintena|Fena);
		delay(10);
		spllo();
print ("floppyrevive(%d): %lux - %lux\n", ++x, &fl, fl.d);

from /sys/src/boot/pc/devfloppy.c:/^floppyrevive (I seem to recall)
reveals that fl.d changes value from a valid address to 0xffffffff.

Now, "fl" is the FController structure, defined in ..../devfloppy.h
(and in devfloppy.c, I removed the second declaration) and I really
cannot figure how one (or more) fields within that structure could
be affected by the operations between.

Also, this only occurs on an old 386/387 platform, with an add-on
ATA and floppy controller.  I have not seen the symptom on the
Pentium I first experimented with.  The symptom itself is obscure:
from trap.c: "exception/interrupt 12".

Clues, anyone?

++L