Prev: Free FAT12/FAT16/FAT32 filesystem (C)
Next: USB CY7C67300 chip HPI
From: Peter Sommerfeld on 11 Jan 2006 14:05
Hi guys,

I am finding that reading the raw data off an SD in my embedded, that
the boot sector is not actually at address 0, but differs from card to
card (ie. my 64 MB has the boot sector at 4E00, and my 128 MB at C600).

Everything else before this is read as 0's.

I am not using any of the secure stuff on the card, just plain-old SPI.
I verifed I am reading the exact values vs. WinHex on a PC and card
reader.

Can anyone provide insight into this? Is there some non-readable secure
stuff on SD cards before the boot sector? Any ideas where I get more
info on this? (I have tons of info on the FAT field descriptions, etc
already).

Thanks!

-- Pete

From: larwe on 11 Jan 2006 14:28
> I am finding that reading the raw data off an SD in my embedded, that
> the boot sector is not actually at address 0, but differs from card to
> card (ie. my 64 MB has the boot sector at 4E00, and my 128 MB at C600).

What boot sector are you talking about - the DOS boot sector (first
sector of the FAT volume) or the MBR?

From: psommerfeld on 11 Jan 2006 15:20
It's the one where the 1st byte is EB and offset 3 in the sector has
the string "MSDOS5.0" on my FAT32-formatted card. I apolozige for not
knowing the correct term, but it must be the DOS boot sector?

-- Pete

From: larwe on 11 Jan 2006 15:25

> It's the one where the 1st byte is EB and offset 3 in the sector has
> the string "MSDOS5.0" on my FAT32-formatted card. I apolozige for not
> knowing the correct term, but it must be the DOS boot sector?

That's the LBR. Removable flash media are formatted as hard disks. They
have an MBR (partition table) at sector 0. If you formatted the card on
Windows the MBR is probably set up so that the first partition is at
cylinder 0 head 1 sector 1 (i.e. you lose the first track on the disk).

Look at my DOSFS code for information on the MBR format and C code to
work out the start of the partition. http://www.zws.com/products/dosfs/

From: Maxim S. Shatskih on 11 Jan 2006 18:21
The card can have the MBR partition table. In this case, the boot sector is
usually sector 63.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim(a)storagecraft.com
http://www.storagecraft.com

"Peter Sommerfeld" <psommerfeld(a)gmail.com> wrote in message
news:1137006351.757006.163310(a)g43g2000cwa.googlegroups.com...
> Hi guys,
>
> I am finding that reading the raw data off an SD in my embedded, that
> the boot sector is not actually at address 0, but differs from card to
> card (ie. my 64 MB has the boot sector at 4E00, and my 128 MB at C600).
>
> Everything else before this is read as 0's.
>
> I am not using any of the secure stuff on the card, just plain-old SPI.
> I verifed I am reading the exact values vs. WinHex on a PC and card
> reader.
>
> Can anyone provide insight into this? Is there some non-readable secure
> stuff on SD cards before the boot sector? Any ideas where I get more
> info on this? (I have tons of info on the FAT field descriptions, etc
> already).
>
> Thanks!
>
> -- Pete
>

 |  Next  |  Last
Pages: 1 2 3 4 5 6
Prev: Free FAT12/FAT16/FAT32 filesystem (C)
Next: USB CY7C67300 chip HPI