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

[Thomas Schmitt]

Hi,

Ronald F. Guilmette wrote:
> Remember that RUFUS *does* set the
> bootable flag and that, as I said already, my goofy motherboard refuses
> to see a USB-connected device as being bootable if the device in question
> contains a single partition that *does* have that flag set.

If this theory is right then it would suffice to set bit 7
of byte 446 of the USB stick to 0 (first byte is number 0).

Pity we do not use the same operating system. But this should
be not too hard to do in any programming language, if you can
open the stick device for read/write operations. 


> I had no idea at that
> time that I needed to set _both_ the bootable flag and the (non-
> standard?) "LBA" flag.  But apparently both are vital.  Now I know.

As producer of MBRs i wonder where that LBA-flag is located.
In bit 0 to bit 6 of byte 446 (where bit 7 means active/bootable) ?
Is any background info known ?
A flag to tell that C/H/S shall be ignored would be interesting.

I am looking at
  https://git.gnome.org/browse/gparted/tree/
but don't find enlightenment.

Ronald:

Can you post a hexdump of the first 512 bytes of the
stick state of which GParted reports that LBA-flag ?
(Actually bytes 440 to 511 are of most interest.)

Are you sure that without LBA-flag it is not recognized ?


> (Actually, someone else in this thread mentioned "LBA" but I failed
> to properly read those comments.  Sorry.)

We mentioned LBA (Logical Block Address) mostly because we
suspected that a high address of the boot image file might
reveil bugs which are not to see on other systems.
There also was the suspicion that the partitioning of the
stick had a stake in the problem.
So it was suggested to try one of the isohybrid ISO images of
the Linux distros, which get their partitioning either from
program isohybrid or from my xorriso. Just to see whether they
do any better and then to analyze the differences.

But i doubt that both programs set an LBA-flag by accident.
And typically, the active/bootable flag is set in isohybrid MBRs.
So they will likely not show up with your mad board.
(Unless you set bit7 in byte 446 to 0.)

Further i cannot tell how to flatly copy an image file onto
USB stick by help of MS-Windows.


Have a nice day :)

Thomas