Re: 264 kernals, bugs, ntsc hack, etc.

From: Hársfalvi Levente <>
Date: Wed, 31 Aug 2011 23:27:03 +0200
Message-ID: <>

On 2011-08-31 20:08, Gerrit Heitsch wrote:

>> I did meet the infamous "28 ff" bug, though (which is IMHO present in
>> all revisions).
> Oh? Never heard of that one. Can you describe it?

Had to recall how that one exactly happens.

In short, if you code in monitor, from time to time, you'll notice that
some bytes around $3000 get overwritten. To be precise: most of the
time, if it happens, $3058 and $3059 are overwritten by $28 and $ff
respectively. ...Most people who developed in monitor, met that one and
its consequences sooner or later.

As it turns out, the problem is the assembler function of the built-in
monitor, interfering with Basic disc routines. "A" would copy some bytes
to $0077 and on. Basic disc routines usually call the "clear ds$"
routine ($CD57), which first checks if ds$ was empty (by checking
whether $79 is 0). If not, it writes $28, and $ff to ($7a),y where y is
$28 and $29 respectively. When using the built-in assembler, and exiting
from monitor (to get a directory, or something like that), the zeropage
addresses assigned to ds$ are almost 100% to be invalid. Now request
directory, or do any other Basic disk I/O operations, and your stuff is
most probably shot. (Whether it'll fail then is another matter - it all
depends whether you're using these locations... sometimes it meant long
hours of debugging mysterious problems, wondering why the hell it all
failed to work once it already did work, sometimes reloading some
previous saved state to start over with, etc. )

> To give you can idea, go to and search for 'V 5619'
> (Search field, upper left corner). I used the one for 28pin on the CPU
> and the one for 40 pin on TED. A _small_ drop of heatsink compound in
> the middle, place on chip, move a bit to spread the compound around.
> Then just a drop of generic adhesive (not epoxy) on each end of the
> heatsink so it connects the exposed part of the chip with the end of the
> heatsink. Let dry for a few days. Done.

Okay, thanks!


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Received on 2011-08-31 22:00:12

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