OS not booting on legacy mode UEFI machines

[interruption]

Hi.

So I have a MBR bootloader that is defined as such:

Code: Select all

(510 bytes of code)
dw 55AAH
(more code)

This works for machines that do not have UEFI support entirely.
But machines that support UEFI (I have two of them, one is older than the other), they can't boot off of my imaged usb drive.
I am confused as to why this is happening. Should I have a FAT header before my code?
Does anyone know why this is happening?

thanks

[zaval]

5.2.1 Legacy Master Boot Record (MBR)
A legacy MBR may be located at LBA 0 (i.e., the first logical block) of the disk if it is not using the
GPT disk layout (i.e., if it is using the MBR disk layout). The boot code on the MBR is not executed
by UEFI firmware.

But in your case, that even is not a valid MBR.

[Brendan]

Hi,

So I have a MBR bootloader that is defined as such:

Code: Select all

(510 bytes of code)
dw 55AAH
(more code)

There's multiple problems with booting from USB flash, so I thought I'd start a "Problems Booting From USB Flash" page in the wiki.


Cheers,

Brendan

[Octocontrabass]

There's multiple problems with booting from USB flash, so I thought I'd start a "Problems Booting From USB Flash" page in the wiki.

Looks good! One thing bothers me though.

Some firmware vendors have decided that USB flash devices should also be able to emulate CD, and support the El Torito specification for USB flash devices.

Do you have any proof for this statement?

[Brendan]

Hi,

Some firmware vendors have decided that USB flash devices should also be able to emulate CD, and support the El Torito specification for USB flash devices.

Do you have any proof for this statement?

I don't have proof and can't remember where I saw it mentioned. I may have got this around the wrong way (some USB flash devices emulate USB CD devices).


Cheers,

Brendan

[Octocontrabass]

I've only ever heard of hybrid ISOs being bootable when written to a USB flash drive. I think the statement on El Torito in the article should be removed until someone can make a more compelling argument.

[MichaelPetch]

Code: Select all

(510 bytes of code)
dw 55AAH
(more code)

This is only an addendum to the other answers regarding booting USB media. But the first thing that struck me is that your boot signature is incorrect. Expressed as a word the boot signature is actually dw 0AA55h or two individual bytes db 55h, 0AAh