Possible issue in "__Lib_FAT32_Driver" of the Fat32 library

[Dany]

Hi,

Concerning the Fat32 library usage:

There is a possible error in the outcome of routine "FAT32_Dev_SectorCount" in unit "__Lib_FAT32_Driver" of the Fat32 example in the mP PIC mpkg file:

Code excerpt:

Code: Select all

   if (1 = ((csdbuf[0] and 0xC0) shr 6)) then
    begin
        size := 0;                             size := size shl 8;
        size := size + (csdbuf[7] and 0x3F);   size := size shl 8;
        size := size + csdbuf[8];              size := size shl 8;
        size := size + csdbuf[9];              size := size shl 0;

        // size is in 0.5MB, get size in sectors (assumed 512 bytes sector size)
        size := size * 1024;  // <--- must be: Size := (Size+1) * 1024
    end

See comment in above code.
The outcome of the unchanged routine will always be 1024 sectors (0.5 MB) too less.

Thanks in advance for changing this!

[dejan.odabasic]

Hello,

Here are the results of 8GB card I tested:

SD_Card_details.png (114.29 KiB) Viewed 4435 times

Best regards.

[Dany]

Hi,

Thanks for your reply.

Well, the difference is only 0.5 Mb on 8 Gb... and I see that the PC calculations are the same as the drivers calculation...

Anyway, I got the info from the "SD Specification Part1, Physical Layer Simplified Specification" document, see https://www.sdcard.org/downloads/pls/.

Extract of the content:

C_SIZE
This field is expanded to 22 bits and can indicate up to 2 TBytes (It is the same as the maximum
memory space specified by a 32-bit block address.)
This parameter is used to calculate the user data area capacity in the SD memory card (not include the
protected area). The user data area capacity is calculated from C_SIZE as follows:
memory capacity = (C_SIZE+1) * 512KByte

That was the reason for my reaction on the "__Lib_FAT32_Driver" code... Perhaps the document is wrong?

p.s. I weakened the title of the post.

[dejan.odabasic]

Hello,

It's just a matter of difference in specification version.
Explanation that you found is covered with following code:

SD card.png (37.4 KiB) Viewed 4416 times

Best regards.

[Dany]

It's just a matter of difference in specification version.
Explanation that you found is covered with following code:

The specification version used for 8Gb cards is the version 2.0. You point in your code to version 1.x.