Hi,
A little spin-off here, about details of how diskROMs load sectors in
page 1...
Maarten ter Huurne <[EMAIL PROTECTED]> wrote:
> What might be an interesting spin-off is whether loading in page 1
> is legal or not.
Absolutely legal. Supported by DOS1 (& DOS2 in other ways) with
various help-routines, and supported by every
(DOS1-compatible, used for SS/DS floppies) diskROM that I have come
across. If it wasn't legal to do this, I'm sure it wouldn't be so
generally supported, so sure this is okay.
> I have been disassembling the NMS8250 diskROM and I
> found a routine that runs in page 2 (!) and reads a sector. The only
> reason for such a routine would be to load data into page 1.
Quite possible (as described in my earlier message)
> Did the
> implementors of that diskROM do something that was not necessary? Is
> it left-over code that is never actually called?
Not unnecessary here. It is however quite possible that you come
across some 'dead code' (not used, but still there) in diskROMs.
Apparantly diskROMs are pieces of code, which between models &
hardware revisions, were updated far more frequent than other system
software, so there are many different ones, some with several bugs
or lousy programming work in it etc. So some dead code in there is
really not unusual.
In the NMS8245 diskROM I disassembled once (it's on my webpages), the
disk-I/O write verification (controlled by DOS verify on/off, using a
flag at F30Dh) was hard-coded as 'off', no verification on write
actions, no matter what this flag says.
But the code for using that flag, and writing sectors WITH
verification, was still in there. After making this disassembly,
changing one or two single instructions was enough to re-enable
support for this verify-flag. And working perfectly.
As before: really not uncommon such things.
> Or is loading to page 1 by the #4010 routine legal after all?
Dutch: ja dus! ;-)
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
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