Date:	Mon, 27 Mar 1995 21:13:24 -0500
From:	dj (DJ Delorie)
To:	mmcmpope AT inet DOT uni-c DOT dk
Cc:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	Re: How to debug after playing with timer-int ?

> >(3) Does anybody have any general advise for how to debug a program involving
> >    interrupt routines.  I sometimes try to use edebug (is that what its

> control. So I usually employ a simple color scheme: When the program
> reaches this point, it changes the background color to red, if this or that
> condition turns out false, it makes the screen blue... If you absolutely

My favorite is these two instructions:

	movb	$0x33, %al
	outb	%al, $0x61

(you'll find them in the "sound" macro in go32/mswitch.asm also :-)

These opcodes are the same in 16 and 32-bit code, don't reference
memory, and cause the speaker to emit a tone (assuming that it's set
up beforehand to be a tone generator).  Then, you can use the "if it
beeped before it rebooted, it got this far" method to isolate the
problems.

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