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Re: USB Booting
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cordata51
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Jan 26 07 12:11 AM
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Hi
I mentioned early about the test bootsector i created when investigating booting from a usb memory stick using hard drive emulation. I posted the file over here
http://board.flatassembler.net/topic.php?p=51973#51973
@wmraim - sorry to hear that it did not work for you. Perhaps you are in the same position i am in. That is my laptop only supports booting from USB using Hard Drive Emulation. If you feel upto it, give that test bootsector a try and lemme know if you get anything out of it. If you do try it, aftr loading it and booting into it, you should notice the light blinking on your PenDrive indicating it is accually reading from the usb device and not somewhere else. Also if it does work, then you should also see in the first page of the memory dump the string "Operating System Missing"!
@Madis731 - Hi madis, its been awhile since i checked out your detailed writeup on bootsector testing and im feeling a little lazy right now to look it over again, but.... depending on how your media is formatted, i dont know many utilities other then DD that have direct access to media devices. I think it is possible that if you do not have the media setup properly, some of these other utilities may not be capable of overwriting the MBR that exists on your flash memory device. I know from experience that Hex Workshop does not have access to the MBR, and i doubt any other hex editing style progra will either. Another thing to be aware of is that in order to accomplish booting from a usb device, your motherboard needs to 1st understand how to control the USB Controller, 2nd needs to be capable of reading and writing to a standardized flash memory device (not all devices follow the standard rules and therefore some may never work), 3rd the motherboard needs to know how to remap Interupt 0x13 request to the USB memory device.
The 3rd is the one problem most people have in that most motherboards only provide hard drive emulation, others only floppy emulation. Also when you mentioned some third party bootsectors, some bootsectors (like the Fat32 bootsector created for menuet) directly access the IDE controler through the i/o ports Instead of using interupt 0x13 and therefore bypass completely the bios calls that the motherboards attempt to remap the usb to.
Finally, when you say
QUOTE
@cordata51: The DD utility writes the image as raw as any other utility and it doesn't change the outcome "Operating system missing".
I really dont fully understand what you mean by "raw". The "Operating System Missing" message comes from the code in the Master Boot Record (MBR) when it fails to find a valid signature (0xAA55 at offset 0x510) or an active partition, if you get my test bootloader working youll see that message in the mbr. I suppose its possible that your motherboard manufacturer coded that same message into there bios, but i think its highly unlikely. The MBR is that secret header contained on the first sector of every drive (excluding floppy disks) which contains information about each partition on the drive, and not many programs that i am aware of can gain access to that sector from within windows, DD is an exception. Check here at some links about that message.....
http://support.microsoft.com/kb/80304
http://home.teleport.com/~brainy/fat32.htm
If your really interested in seeing the MBR on the USB flash and dont want to or cant get the test boot sector working, i used the following DD command to dump the entire memory space from my USB flash drive....
dd if=\\?\Device\Harddisk2\Partition0 of=c:\temp\usb2.img bs=1M
you may have to change the HarddiskX number to get the proper device from your pc. and the MBR will be the first 512 bytes of data in that dump.
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