@echo off
set qemu=qemu-system-x86_64.exe
if not exist %SystemRoot%\SysWOW64 set qemu=qemu.exe
cd ..
%qemu% -L . -localtime -hda bootstrap32\bootstrap32.img    

  @echo off
  echo Requires a non partitioned FAT32 formatted flash drive.

  set drive=
  set /p drive=bootstrap32 flash drive letter:

  set format=N
  set /p format=Do you want to format drive %drive%:? (Y/N)
  if not %format%==Y (
    if not %format%==y (
      goto :next
    )
  )
  dd\dd.exe --filter=removable if=/dev/zero od=%drive%: bs=512 count=1 2>NUL
  echo Remove and re-insert the flash drive.
  echo (Ignore Windows message to format the drive!)
  pause

  format %drive%: /FS:FAT32 /Q

:next
  dd\dd.exe id=%drive%: of=temp bs=512 count=1 2>NUL

  dd\dd.exe if=bootstrap32.img of=temp bs=1 skip=48 seek=48 count=4 2>NUL
  dd\dd.exe if=bootstrap32.img of=temp bs=1 skip=90 seek=90 count=422 2>NUL
  dd\dd.exe if=bootstrap32.img of=temp bs=512 skip=1 seek=1 count=31 2>NUL

  dd\dd.exe --filter=removable if=/dev/zero od=%drive%: bs=512 count=1 2>NUL
  echo Remove and re-insert the flash drive.
  echo (Ignore Windows message to format the drive!)
  pause

  dd\dd.exe --filter=removable if=temp od=%drive%: 2>NUL
  del temp >NUL
  copy /Y root\*.* %drive%:
  pause    

KERNEL  BIN
12345678123    

what would be the correct method of taking control of the PIT and its interrupt?
Obviously, I need to use the timer interrupt yet I want the floppy BIOS calls to remain functional.

Secondly, what tool do you use to create an image of the USB disk?

running bootstrap32.cmd prepares the physical medium, but I would like to test using QEMU rather
than hardware.

Also this bootloader/bootstrap32.cmd does not work on my hardware. When booting with only the USB
device connected, it errors,

and if there is any other boot device connected (but on a lower boot order) it just boots that instead.
Im not sure if that is due to my hardware, or a failure of bootstrap32.cmd

I want to avoid BIOS usage

what drive number can be used al int 13h to point to usb device?

Thank's Dex, I want to avoid BIOS usage, despite a bunch of technical documentation about USB interface i am not able to implement any working code to acces mass storage device... I am completely lost. Have you any example?
On the other hand... what drive number can be used al int 13h to point to usb device?
Thank's again

Your better of using bootstrap32, because the work that is needed to code a usb stack is a lot,
thats why a book has been written about it.

Probably a good idea to get rid of A20 code from Fat32 VBR

and add support for LBA

and switch to reading disk one sector(512b) per one int13h call (for legacy reasons)

and remove protected mode switch

I am just saying that you made all the mistakes that a beginner makes inside MBR or VBR. Especially
when you have second stage bootloader.

It's only a legacy issue that the PC starts up in real mode. There's no reason why the PC can't startup in PM32
with BIOS access. Of course, that's the path taken by EUFI.