Hi folks,
I need to utilize a known-to-work FAT16/32 library for reading SD cards. I'm seeing peculiar boot record data that doesn't make any sense to me. I'm hoping somebody here has preceded me in getting SD cards readable with FAT FS libraries.
We've used both dosfs and fat_io (both free to use from the web) with success on USB flash drives and rotating magnetic drives. Now the simple process of interfacing to SD cards shows problems in the volume boot record (VBR) sector address held in the master boot record (MBR). Specifically, the VBR start sector is sector 8192 for all three FAT32 SD card samples we're using but no valid VBR exists at that sector. Our single FAT16 SD card sample indicates the correct VBR start sector (sector 39) because we can read all files and directories on it.
An important data point is that I've been able to find a valid VBR at sector 16 for all my FAT32 cards. Sector 16 just happens to be the sector at byte address 8192 (just a coincidence or significant?). If I redirect the VBR read mechanism to sector 16, I get additional API usage failures.
Is there some sort of important differences with SD cards that I need to take into account for FAT32 file systems?
Thanks = John Speth