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theesemtheesem wrote:Hi,

As I understand You have already verified that all these machines boot from USB without problems, it's just Your code that does not seem to work. I'm not an expert in this, since my kernel is multiboot compliant and I use grub to boot it, but what comes to mind ist that possibly the drive number You are using is wrong? What is Your setup in bochs/qemu? Do You have any other hdd images set up? What is the setup in the "real" machines? Do these have any hard drives at all, or is it just the usb stick?

I cans see that Your drive number is hardcoded to 0x80. Maybe it would be better to grab the boot drive number from the BIOS? There is no guarantee that USB devices will be numbered starting from 0x80 even if no other hard drives are present.

Cheers,
Andrew

theesemtheesem wrote:Hi,

As I said I am no expert with bootsector code, but possibly You are making some assumptions about the "disk" geometry that are not necessarily true. Remember that booting from USB uses an emulation layer in the BIOS and You can't assume what the stick is emulated as. The way You invoke qemu makes Your image the first ATA hard drive, so obviously it should be handled as a hard drive. But that does not need to be true with real hardware bioses.

Have a look at this: http://board.flatassembler.net/topic.php?t=12389

The guy uses the int 13 / function 08h to get the emulated drives parameters and goes from there.

Can You print the stored value of dl to see what actually gets passed from the BIOS?

Cheers,
Andrew

DavidCooper wrote:Are you sure you've put your code at the right place on the flash drive? I'm wondering if you've copied it all to the start of a partition instead of to the beginning of the physical drive - that would explain why it works as a disk image when your code certainly is placed at the start of the file, but not on the flash drive where an MBR may be running first before handing control to your code at the start of a partition which will then load in the MBR again and display random garbage from that.

If this turns out to be what's going on, don't wipe out the MBR, but retain it and learn how to use it properly - it's much more reliable to boot a flash drive via an MBR rather than sticking your VBR there, so keep your code at the start of a partition. You'll need to work out which sector is the first of the partition and adjust your DAP to line up on that sector.

dd bs=512 if=extendedDrive of=\\.\T:
dd bs=512 count=3 seek=3 if=loadKernel of=\\.\T:

dd bs=4096 count=16384 if=\\.\T: of=O:\OS_DISK_IMAGE\fubuki

GB80CPU wrote: I've read somewhere the alignment of the DAP might be important. It should be in memory at location 0x7DE0, 16 byte alignment. Is this really important?

        mov si, 0
        mov di, 0
        mov ax, 0x1000
        mov ds, ax
        mov ax, 0xB800
        mov es, ax
        mov cx, 80
        mov bl, 0x02
.loop:
        movsb
        mov [es:di], bl
        inc di
        loop .loop

loadSecondStage:
        xor ax, ax  ;; Should be redundant.
        mov ds, ax
 
        xor ah, ah
        mov dl, [driveNumber]
        int 0x13
        jc fail
 
        xor ax, ax
        mov ds, ax
 
        mov ah, 0x42
        mov dl, [driveNumber]
        mov si, DAP
        int 0x13
        jc fail

GB80CPU wrote:

Code: Select all

dd bs=512 if=extendedDrive of=\\.\T:
dd bs=512 count=3 seek=3 if=loadKernel of=\\.\T:

dd bs=4096 count=16384 if=\\.\T: of=O:\OS_DISK_IMAGE\fubuki

	dd if=mbr of=/dev/sdb seek=0 conv=sync
	dd if=system of=/dev/sdb seek=1 conv=sync

dd.exe bs=512 count=16384 if=\\.\PHYSICALDRIVEn of=output

bwat wrote:

GB80CPU wrote:

Code: Select all

dd bs=512 if=extendedDrive of=\\.\T:
dd bs=512 count=3 seek=3 if=loadKernel of=\\.\T:

dd bs=4096 count=16384 if=\\.\T: of=O:\OS_DISK_IMAGE\fubuki

You probably want to give the "conv=sync" option to dd like I do in my installation:

Code: Select all

	dd if=mbr of=/dev/sdb seek=0 conv=sync
	dd if=system of=/dev/sdb seek=1 conv=sync

DavidCooper wrote:No need to feel stupid - it's a common mistake, and one I've made myself. As for using dd, I've never dared to in case I trash the internal hard drive, so I just stick to using HxD to write to flash drives so that it can be done without any risk.