Where should I discuss SD/MMC FAT issues?


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    Quote Originally Posted by JD123 View Post
    I found the file size information in the directory listing at offset 28 and this falls into what I was expecting based on that I've read. Problem is that the file size information is a 4 byte Dword and FAT specs call for the 4 bytes to START at offset 28. In reality, I would have thought that the "10" for the file size would have been in offset 31 (LSByte of the 4 bytes). I'm trying to figure out where I place the additional 3 bytes of the file size information. I can't find anything to support that the file size should be written low byte first and that wouldn't make sense anyway. So, I'm thinking that there's something wrong with my understanding of where the bytes are stored.
    Isn't the file size in FAT32 stored at 2 different places? And both of them have to be identical? I forget...it's been awhile since I read the FAT32 documentation...

    I'll have no choice but to add RAM to my hardware.
    I built an MP3 player awhile back based off an 18F4620 reading from CF cards in IDE mode. Had enough ram to buffer 6 complete sectors with room left over for a load of variables.
    Also, if that's not enough, look into the F-RAM options. Serial EEPROM just like a 24C256 type, but it's ram, read/write just as fast, not slow writes/fast reads like eeprom, and practically unlimited lifetime.

    understand the offset location and data style (MSB or LSB first) of the file size data I'd appreciate reading your thoughts.
    Keep track of your little and big ENDIAN formats according to the FAT32 documentation. I don't know how many times that sort of thing tripped me up bad...

    EDIT: Just dug out the FAT32 doc file.
    Is the file you're basing your FAT32 code from called 'fatgen103.doc'?
    If so, that file has a few issues in itself, wrong places for some values, some values omitted, and so on...
    gain, it's been awhile. I'll see if I can't dig up the specifics.
    Last edited by skimask; - 12th March 2008 at 17:03.

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