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Hi all,

New to the forum (and to OS coding really) except for writing a pmode system for DOS so many years ago I can hardly remember

I've started working on an OS purely for interest sake and have gone with a 2 stage boot-loader design.

Sofar all the bits of it have come together under bochs nicely (using floppy image).

I just wanted to find out if A) there are any "code" differences one should take into account when booting from a USB device, or CD for that matter.

I thought I'd take the time now to test what I have sofar on a few real machines and setups, starting with a USB boot on my laptop.
I've written the 1st and 2nd stage loaders to a USB memory stick but I'm not having any joy in getting it to boot.. All i get is either a flashing cursor (not even executing/loading the 1st stage) or a message that the media is not bootable.

I'm running an AMI bios in this laptop, are there any known problems with it booting of USB?

Lots of questions.. Thanks for any help in advance!

If youre pc is able to boot an usb device it should not be a problem. The only thing you have to take into account is that your bios might use a different approach to accessing the drive. A floppy in general has 2 heads, 18 sectors and 2880 tracks or something a like. When using an usb device i found out that is is up to the bios to assign values for the head/sector/track. I tested on three different machines and got three different results. Best thing to do is read them with int 0x10 function 8 (GetDriveParameters). Then you can use those parameters for reading the drive. This is what i do and it works perfectly. It will automatically run on harddisk and floppy.

Thanks for the info. I will use those returned values when reading the 2nd stage loader.

My problem though seems to be happening before I even do anything (code wise).

The bios will load the 1st sector (1st stage loader automatically), but it doesn't I just get a non-bootable media error come up sometimes and others a blank screen with a flashing cursor. The 1st stage loader has the 55aa end signature marker, works under bochs etc.

So I was wondering if certain AMI bioses which are supposed to be able to boot from usb, don't work properly

my greatest obsticle regarding usb boting has been getting the actual bootsector onto the usb device. I tryed rawrite, but couldnt find any useable parameters, itryed other stuff too, but eventually the only solution to my problem was copy/paste using a lowlevel hex editor i found (by the way i havent been able to find it again and i need it!).
I could choose to open the first sector of any device and then it was just a matter of pasting the binarys and save.

I would like another solution to that problem.

what about using dd?

Zacariaz wrote:my greatest obsticle regarding usb boting has been getting the actual bootsector onto the usb device. I tryed rawrite, but couldnt find any useable parameters, itryed other stuff too, but eventually the only solution to my problem was copy/paste using a lowlevel hex editor i found (by the way i havent been able to find it again and i need it!).
I could choose to open the first sector of any device and then it was just a matter of pasting the binarys and save.

I would like another solution to that problem.

If you use cygwin or linux you could use dd. It works but can be dangerous, using dd wrong can result in a very clean harddisk .

I only use usb stick with led indication:

then use: dd if=/dev/sdf of=/dev/null to check if the device i address is indeed the usb stick. otherwise try sdb, sdc, sdd, sde etc. when i have located the correct device i use dd of=/dev/sdf if=bin/drive.img where sdf is the device found with the above check.

Hey,

I wrote a program for this purpose, I can send you a copy of it if you like, just send me your email addy.

It basically uses win i/o low level device names like \\.\F: to access a logical device sector by sector.

The little app I made can read/write between devices and files so it's also useful for capturing sectors from disks... works with usb/floppy/hdisk.