fat32_base.c

FAT32代码

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
//					        FAT32 File IO Library
//								    V2.0
// 	  							 Rob Riglar
//						    Copyright 2003 - 2007
//
//   					  Email: [e-mail]
//
//-----------------------------------------------------------------------------
//
// This file is part of FAT32 File IO Library.
//
// FAT32 File IO Library is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// FAT32 File IO Library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with FAT32 File IO Library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
#include "FAT32_Definitions.h"
#include "FAT32_Base.h"
#include "FAT32_Table.h"

//-----------------------------------------------------------------------------
// FAT32_FindLBABegin: This function is used to find the LBA Address of the first
// volume on the disc. Also checks are performed on the signature and identity
// codes to make sure the partition is FAT32.
//-----------------------------------------------------------------------------
BOOL FAT32_FindLBABegin(BYTE *buffer, UINT32 *lbaBegin)
{	
	if (buffer==NULL)
		return FALSE;

	// Load MBR (LBA 0) into the 512 byte buffer
	if (!FAT_ReadSector(0, buffer))
		return FALSE;
	
	// Make Sure 0x55 and 0xAA are at end of sector
	if (GET_16BIT_WORD(buffer, Signature_Position)!=Signature_Value) 
		return FALSE;
		
	// TODO: Verify this 

	// Check the partition type code
	switch(buffer[PARTITION1_TYPECODE_LOCATION])
	{
	case 0x0B: break;
	case 0x06: break;
	case 0x0C: break;
	case 0x0E: break;
	case 0x0F: break;
	case 0x05: break;
	default:
		if (buffer[PARTITION1_TYPECODE_LOCATION] > 0x06)
			return FALSE;
		break;
	}

	// Read LBA Begin for FAT32 File system is located for partition
	*lbaBegin=GET_32BIT_WORD(buffer, PARTITION1_LBA_BEGIN_LOCATION);

  	// Return the LBA address of FAT table
	return TRUE;			
}
//-----------------------------------------------------------------------------
// FAT32_LBAofCluster: This function converts a cluster number into a sector / 
// LBA number.
//-----------------------------------------------------------------------------
UINT32 FAT32_LBAofCluster(UINT32 Cluster_Number)
{
	return ((FAT32.cluster_begin_lba + ((Cluster_Number-2)*FAT32.SectorsPerCluster)));
}
//-----------------------------------------------------------------------------
// FAT32_Init: Uses FAT32_FindLBABegin to find the LBA for the volume, 
// and loads into memory some specific details of the partitionw which are used 
// in further calculations.
//-----------------------------------------------------------------------------
BOOL FAT32_Init(void)
{
	BYTE buffer[512];

	BYTE Number_of_FATS;
	UINT16 Reserved_Sectors;
	UINT32 LBA_BEGIN;
	UINT32 FATSz;
	UINT32 RootDirSectors;
	UINT32 TotSec;
	UINT32 DataSec;
	UINT32 CountofClusters;

	FAT32_InitFatBuffer();

	// Check Volume 1 and find LBA address
	if (FAT32_FindLBABegin(buffer, &LBA_BEGIN))
	{
		FAT32.lba_begin = LBA_BEGIN;

		// Load Volume 1 table into sector buffer
		if (!FAT_ReadSector(LBA_BEGIN, buffer))
			return FALSE;

		// Make sure there are 512 bytes per cluster
		if (GET_16BIT_WORD(buffer, 0x0B)!=0x200) 
			return FALSE;

		// Load Parameters of FAT32	 
		FAT32.SectorsPerCluster = buffer[BPB_SecPerClus];
		Reserved_Sectors = GET_16BIT_WORD(buffer, BPB_RsvdSecCnt);
		Number_of_FATS = buffer[BPB_NumFATs];
		FAT32.fat_sectors = GET_32BIT_WORD(buffer, BPB_FAT32_FATSz32);
		FAT32.RootDir_First_Cluster = GET_32BIT_WORD(buffer, BPB_FAT32_RootClus);
		FAT32.fs_info_sector = GET_16BIT_WORD(buffer, BPB_FAT32_FSInfo);

		// First FAT LBA address
		FAT32.fat_begin_lba = LBA_BEGIN + Reserved_Sectors;

		// The address of the first data cluster on this volume
		FAT32.cluster_begin_lba = FAT32.fat_begin_lba + (Number_of_FATS * FAT32.fat_sectors);

		if (GET_16BIT_WORD(buffer, 0x1FE)!=0xAA55) // This signature should be AA55
			return FALSE;

		// Calculate the root dir sectors
		RootDirSectors = ((GET_16BIT_WORD(buffer, BPB_RootEntCnt) * 32) + (GET_16BIT_WORD(buffer, BPB_BytsPerSec) - 1)) / GET_16BIT_WORD(buffer, BPB_BytsPerSec);
		
		if(GET_16BIT_WORD(buffer, BPB_FATSz16) != 0)
			FATSz = GET_16BIT_WORD(buffer, BPB_FATSz16);
		else
			FATSz = GET_32BIT_WORD(buffer, BPB_FAT32_FATSz32);  

		if(GET_16BIT_WORD(buffer, BPB_TotSec16) != 0)
			TotSec = GET_16BIT_WORD(buffer, BPB_TotSec16);
		else
			TotSec = GET_32BIT_WORD(buffer, BPB_TotSec32);

		DataSec = TotSec - (GET_16BIT_WORD(buffer, BPB_RsvdSecCnt) + (buffer[BPB_NumFATs] * FATSz) + RootDirSectors);

		CountofClusters = DataSec / FAT32.SectorsPerCluster;

		if(CountofClusters < 4085) 
			// Volume is FAT12 
			return FALSE;
		else if(CountofClusters < 65525) 
			// Volume is FAT16
			return FALSE;

		return TRUE;
	 }
	 else
		return FALSE;
}