[syslinux] After USB boot problems on Gigabyte GA-M55Plus-S3G

[Thomas Schmitt]

Hi,

> I am assuming that the CHS values that you posted are not the 
> "amount" (Nx255x63), but the "position"

The CHS values which i reported were read directly
from the partition table by a hex editor.
(fdisk's CHS complaints match my reading.)


> "CHS 982 / 254 / 63" = "LBA 15'791'894"
> we can see that the FAT32 filesystem limit (15'794'175) is located 
> beyond the partition limit (15'791'894).

That would be ok with the LBA size of the partition,
which is exactly 15'794'175.
(This was computed from the 32-bit values out of the
 partition table: Start LBA + block count - 1.
 My values match the ones displayed by fdisk -lu)


My current theory is that vendors prefer to record
a cylinder aligned end CHS address over recording
an end CHS address which exploits the whole capacity.
This is used as an (inofficial ?) protocol to publish
the CHS factors H' and S'.


> So, the report should had said, either:
>  _ End   LBA 15791894 = CHS  982 254  63
> or:
>  _ End   LBA 15794175 = CHS  983  36  13

Yep. This is in sync with fdisk, which complains:

  Partition 1 has different physical/logical endings:
  phys=(982, 254, 63) logical=(983, 36, 13)

The theory matches with my 2 GB stick too.

Next i manipulated the 8 GB partition end CHS to be
  982 253 63
and (hoorray !) the complaint is
  phys=(982, 253, 63) logical=(987, 3, 13)
which matches
  15794175 = 987 * (253 + 1) * 63 + 3 * 63 + (13 - 1)

Finally i understand what fdisk means when it warns
about a differing "logical" ending.
It deduces the H' and S' factors from the end CHS and
then checks whether they make the end CHS match the
end LBA.

This one looks cool:
  Partition 1 has different physical/logical beginnings (non-Linux?):
     phys=(0, 1, 1) logical=(3, 0, 4)
  Partition 1 has different physical/logical endings:
     phys=(982, 3, 5) logical=(789708, 3, 1)


Have a nice day :)

Thomas