> My idea: why not indicate a big sector number with the highest bit of
> the drive number (passed with A register)?
> If passed to an older driver/part of the system, this would be read
> as drive number beyond 127 ('ridiculous'), and any action will surely
> be refused in this case, with an error code to go with it.
> -It's 100% compatible, no FFFFh sector number exception
> -The 16 bits used previously for the sector number, can be used as
> normal, to pass the lower 16 bits of the sector number, instead of
> wasting this with a dummy FFFFh value
The idea is not bad but (as with my method) where to hold high
sector number? IX IY and shadow registers are out of question -
the arguments *must* stand inter-slot call.
And what is better in my approach (at least when applying patch
to existing kernels) - it IMHO needs less of patching. Your
approach needs a patch to sector I/O call dispatcher -> it uses
drive number to determine slot of ROM of the selected drive.
My - not. But anyway, i already done the code :-) So wait for
test results.
> -You can use some special values (FFh, FEh, FDh etc.) for the drive
> number to indicate sub-functions, and use this for instance to
> 'inquire' about supported features, locations of extra info etc. (you
> might use this through other entries rather than DISKIO).
No, better not. This makes the routines more complex and leads to
unnecessary waste of time during _any_ read or write. BIOS functions
IMHO must be as straightforward as possible.
-- EV
[MSX Maniac][Pendorian Wannabe][Tubed Audiophile]
[email:[EMAIL PROTECTED]] [www.glasnet.ru/~msxegor]
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