Storage

MMC/SD FAT16 FAT free clusters calculate

Hello there,

maybe someone can tell me where is my mistake when I calculate free clusters in FAT table.
I have read tons info about FAT16, but anyway something wrong in my code. I compare my results with results giving WinHex or simple Win. So my code :

.........
ptrInt = &DataBuffer[0x0B];
BytesPerSector = *ptrInt;

SectorsPerCluster = DataBuffer[0x0D];

ptrInt = &DataBuffer[0x0E];
ReservedSectors = *ptrInt;

NumberFats = DataBuffer[0x10];

ptrInt = &DataBuffer[0x16];
SectorsPerFat = *ptrInt;

ptrLong = &DataBuffer[0x20];
NumberSectors = *ptrLong;

ptrInt = &DataBuffer[0x1C];
HidenSectors = *ptrInt;


FirstFatSector = HidenSectors + ReservedSectors;
LastFatSector = FirstFatSector + SectorsperFat;
Root_Dir_Start = ReservedSectors + NumberFats * SectorsPerFat;
First_Data_Sector = Root_Dir_Start + 32;
Usable_Clusters = (NumberSectors - (First_Data_Sector + 1)) / SectorsPerCluster; // Total available clusters
Capacity = BytesPerSector * SectorsPerCluster * Usable_Clusters;

there any problems - formulas works great,
but there I'm stuck :

Sector = FirstFatSector;
freeClusters = 0;

while( Sector < LastFatSector )
{
Mmc_Read_Sector(Sector, DataBuffer);

for(i=0; i<256; i++) // i - FAT entries. 256 - in FAT any entry is 2 bytes long, so 512/2 = 256
{
if((DataBuffer [i*2]== 0x00) && (DataBuffer [(i*2)+ 1]== 0x00))
freeClusters++;
}
Sector++;
}

......

result ==> freeClusters = 61450 - a little to big!

but WinHex show me another value - 61243.

So I'll be deeply thankful

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