//###########################################################
// File: fat.c
//
// For FAT12, FAT16 and FAT32
// FAT32 not tested yet
// Only for first Partition
// Only for drives with 512 bytes per sector (the most)
//
// Based on a White Paper from MS
// FAT: General Overview of On-Disk Format
// Version 1.03, December 6, 2000
//
// MBR MasterBootRecord
// PC intern 4
// M.Tischer
// Data Becker
//
// Organisation of a FAT formatted drive:
// ======================================
// MBR including Partitiontable's
// Hidden Sectors
//
// First Partition
// Bootsector 1
// Reserved Sectors
// FAT1
// FAT2
// ...
// FATn
// RootDirectory (not used if FAT32)
// Data Region
//
// Second Partition
// Bootsector 2
// Reserved Sectors
// .....
//
//#########################################################################
// Last change: 09.05.2004
//#########################################################################
// holger.klabunde@t-online.de
// http://home.t-online.de/home/holger.klabunde/homepage.htm
//#########################################################################
// Compiler: AVR-GCC 3.2
//#########################################################################
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#include "dos.h"

unsigned char dirbuf[BYTE_PER_SEC];   //buffer for directory sectors
unsigned char iob[BYTE_PER_SEC];      //file i/o buffer

#ifdef USE_FATBUFFER
 unsigned char fatbuf[BYTE_PER_SEC];   //buffer for FAT sectors
#endif

unsigned long FirstDataSector; 
unsigned long FirstRootSector; 

unsigned long FATFirstSector;  
unsigned char FATtype;         
#ifdef USE_FAT32
 unsigned long FAT32RootCluster;
#endif

#ifdef USE_FATBUFFER
 unsigned long FATCurrentSector;
 #ifdef DOS_WRITE
 unsigned char FATStatus; // only for FAT write buffering
 #endif
#endif

unsigned char secPerCluster;


#ifdef USE_FAT32
 unsigned long FirstDirCluster;
#else
 unsigned int FirstDirCluster;
#endif

unsigned long RootDirSectors;

//use some global variables for file access
#ifdef USE_FAT32
 unsigned long FileFirstCluster;     //first cluster of file
 unsigned long FileCurrentCluster;   //actual cluster in use
#else
 unsigned int FileFirstCluster;     //first cluster of file
 unsigned int FileCurrentCluster;   //actual cluster in use
#endif

unsigned long FileCurrentSector;    //sector with last data read/written
unsigned long File1stClusterSector;//  1st sector of cluster in use
unsigned long FileClusterCount;     //clusters read (not really)
unsigned long FileBytePerCluster;   //bytes per cluster
unsigned long FileDirSector;        //sector with dir entry of file
unsigned char FileDirOffset;        //offset to file entry in FileDirSector
unsigned long FileSize;
unsigned long FilePosition;         //actual position when reading file         
unsigned char FileFlag;		    //read or write
unsigned char FileAttr;		    //file attribute
unsigned char FileName[8];
unsigned char FileExt[3];

#ifdef USE_FAT32
 unsigned long endofclusterchain; //value for END_OF_CLUSTERCHAIN 
 unsigned long maxcluster;	 // last usable cluster+1
#else
 unsigned int endofclusterchain; //value for END_OF_CLUSTERCHAIN 
 unsigned int maxcluster;	 // last usable cluster+1
#endif

unsigned long maxsect;           // last sector on drive

#ifdef USE_FATBUFFER
//############################################################
void UpdateFATBuffer(unsigned long newsector)
//############################################################
{
 if(newsector!=FATCurrentSector) // do we need to update the FAT buffer ?
  {
#ifdef DOS_WRITE
   if(FATStatus>0)
    {
     WriteSector(FATCurrentSector,fatbuf); // write the old FAT buffer
     FATStatus=0; // flag FAT buffer is save
    } 
#endif
   ReadSector(newsector,fatbuf); //read FAT sector
   FATCurrentSector=newsector;
  } 
}
#endif

//############################################################
// get next clusternumber of fat cluster chain
#ifdef USE_FAT32
 unsigned long GetNextClusterNumber(unsigned long cluster)
#else
 unsigned int GetNextClusterNumber(unsigned int cluster)
#endif
//############################################################
{
#ifdef USE_FAT12
 unsigned int tmp, secoffset;
 unsigned long fatoffset;
#endif

 union Convert *cv;

 if(cluster<maxcluster) //we need to check this ;-)
  {

#ifdef USE_FAT12
   if(FATtype==FAT12)
    {
     //FAT12 has 1.5 Bytes per FAT entry
     fatoffset= (cluster * 3) >>1 ; //multiply by 1.5 (rounds down)
     secoffset = fatoffset % BYTE_PER_SEC; //we need this for later
     fatoffset= fatoffset / BYTE_PER_SEC; //sector offset from FATFirstSector
 
#ifdef USE_FATBUFFER
     UpdateFATBuffer(FATFirstSector + fatoffset);
     if(secoffset == (BYTE_PER_SEC-1)) //if this is the case, cluster number is
                                   //on a sector boundary. read the next sector too
      {
       tmp=(unsigned int)fatbuf[BYTE_PER_SEC-1]; //keep first part of cluster number
       UpdateFATBuffer(FATFirstSector + fatoffset +1 ); //read next FAT sector
       tmp+=(unsigned int)fatbuf[0] << 8; //second part of cluster number
      }
     else
      {
       cv=(union Convert *)&fatbuf[secoffset];
       tmp=cv->ui;
      } 
#else //#ifdef USE_FATBUFFER
     ReadSector(FATFirstSector + fatoffset,dirbuf); //read FAT sector
     if(secoffset == (BYTE_PER_SEC-1)) //if this is the case, cluster number is
                                   //on a sector boundary. read the next sector too
      {
       tmp=(unsigned int)dirbuf[BYTE_PER_SEC-1]; //keep first part of cluster number
   
       ReadSector(FATFirstSector + fatoffset +1,dirbuf ); //read next FAT sector

       tmp+=(unsigned int)dirbuf[0] << 8; //second part of cluster number
      }
     else
      {
       cv=(union Convert *)&dirbuf[secoffset];
       tmp=cv->ui;
      } 
#endif //#ifdef USE_FATBUFFER

     if(cluster & 0x01) tmp>>=4; //shift to right position
     else               tmp&=0xFFF; //delete high nibble

     return (tmp);
    }//if(FATtype==FAT12)
#endif //#ifdef USE_FAT12

#ifdef USE_FAT16
   if(FATtype==FAT16)
    {
     //two bytes per FAT entry
#ifdef USE_FATBUFFER
     UpdateFATBuffer(FATFirstSector + (cluster * 2) / BYTE_PER_SEC);
     cv=(union Convert *)&fatbuf[(cluster * 2) % BYTE_PER_SEC];
#else //#ifdef USE_FATBUFFER
     ReadSector(FATFirstSector + (cluster * 2) / BYTE_PER_SEC, dirbuf);
     cv=(union Convert *)&dirbuf[(cluster * 2) % BYTE_PER_SEC];
#endif //#ifdef USE_FATBUFFER

     return(cv->ui);
    }//if(FATtype==FAT16)
#endif //#ifdef USE_FAT16

#ifdef USE_FAT32
   if(FATtype==FAT32)
    {
     //four bytes per FAT entry
#ifdef USE_FATBUFFER
     UpdateFATBuffer(FATFirstSector + (cluster * 4) / BYTE_PER_SEC);
     cv=(union Convert *)&fatbuf[(cluster * 4) % BYTE_PER_SEC];
#else //#ifdef USE_FATBUFFER
     ReadSector(FATFirstSector + (cluster * 4) / BYTE_PER_SEC, dirbuf);
     cv=(union Convert *)&dirbuf[(cluster * 4) % BYTE_PER_SEC];
#endif //#ifdef USE_FATBUFFER

     return( cv->ul & 0x0FFFFFFF );
    }//if(FATtype==FAT32) 
#endif //#ifdef USE_FAT32
  }
  
// return 0; //this means free cluster. don't do it
 return DISK_FULL; //return impossible cluster number
}

//###########################################################
//first datacluster is cluster 2 !
#ifdef USE_FAT32
 unsigned long GetFirstSectorOfCluster(unsigned long n)
#else
 unsigned long GetFirstSectorOfCluster(unsigned int n)
#endif
//###########################################################
{
 return (((n - 2) * secPerCluster) + FirstDataSector);
}

#ifdef DOS_WRITE
//###########################################################
#ifdef USE_FAT32
 unsigned long AllocCluster(unsigned long currentcluster)
#else
 unsigned int AllocCluster(unsigned int currentcluster)
#endif
//###########################################################
{
#ifdef USE_FAT32
 unsigned long cluster;
#else
 unsigned int cluster;
#endif

// do this if you want to search from beginning of FAT
// cluster=FindFreeCluster(0); //get next free cluster number
 cluster=FindFreeCluster(currentcluster); // get next free cluster number
 if(cluster!=DISK_FULL && cluster<=maxcluster) // disk full ?
  {
    // insert new cluster number into chain
    // currentcluster=0 means: this is a new cluster chain
    if(currentcluster>0) WriteClusterNumber(currentcluster,cluster);

   // mark end of cluster chain
#ifdef USE_FAT12
   if(FATtype==FAT12) WriteClusterNumber(cluster,0xFFF); 
#endif
#ifdef USE_FAT16
   if(FATtype==FAT16) WriteClusterNumber(cluster,0xFFFF); 
#endif
#ifdef USE_FAT32
   if(FATtype==FAT32) WriteClusterNumber(cluster,0x0FFFFFFF); 
#endif
  }

 return cluster;
}
#endif //DOS_WRITE

#ifdef DOS_WRITE
//###########################################################
// go through the FAT to find a free cluster
#ifdef USE_FAT32
 unsigned long FindFreeCluster(unsigned long currentcluster)
#else
 unsigned int FindFreeCluster(unsigned int currentcluster)
#endif
//###########################################################
{
#ifdef USE_FAT32
 unsigned long cluster;
#else
 unsigned int cluster;
#endif

 cluster=currentcluster+1; // its a good idea to look here first
                           // maybe we do not need to search the whole FAT
                           // and can speed up free cluster search
                           // if you do not want this call FindFreeCluster(0)