[syslinux] cbios disk read problems

[Ram Yalamanchili]

On 5/3/07, Andrew Goodbody <agoodbody at itronix.co.uk> wrote:
> Ram Yalamanchili wrote:
> > Does anyone have experience with cbios intricacies or why this might
> > be happening? Thanks for any help.
> >
> > --
> > Ram
>
> I'm a bit rusty on this sort of thing but you have to be very careful
> with CHS translations. If the algorithm used at format/write time is not
> the same as the algorithm used at read time then you will get issues
> such as this. eg you can get problems formatting and filling a disk on a
> machine with AMI BIOS and then trying to boot it on a machine with a
> Phoenix BIOS.
>
> Andrew
>
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>

Hmm, I actually see this issue on both the machines I have here (Dell
laptop D410 and an AMI bios box). I think, in general there is
something wrong in the code. The algorithm to calculate CHS for reads
is the same one Peter wrote for chain.c32, and I confirmed from
wikipedia.

The disk was made entirely with mkdiskimage and mtools/mkfs.vfat. I
think this is unlikely, but is it possible that the cbios reads dont
support reading after certain disk region? Reading the 70k'ish sector
is around offset 34MB.. hmm..

thanks.