fat.c

来自「51环境下的FAT及FAT32文件系统源码」· C语言 代码 · 共 62 行

#include "common.h"
#include "fat.h"
#include "tpbulk.h"
#include "usb.h"
////////////////////////////////////////
extern SYS_INFO_BLOCK xdata DeviceInfo;
extern FILE_INFO xdata ThisFile;
unsigned int FatSectorPointer=-1;
extern UINT8 xdata FATBUF[512];

////////////////////////////////////////
unsigned int ThisFatSecNum(unsigned int clusterNum)
{
   unsigned int temp;
   temp=clusterNum*2;
   temp=temp/DeviceInfo.BPB_BytesPerSec;
   temp=temp+DeviceInfo.FatStartSector;
   return temp;
}

unsigned long FirstSectorofCluster(unsigned int clusterNum)
{
	unsigned long temp;
	temp=clusterNum-2;
	temp=temp*DeviceInfo.BPB_SecPerClus;
	temp=temp+DeviceInfo.FirstDataSector;
	return temp;
}

unsigned int ThisFatEntOffset(unsigned int clusterNum)
{
	unsigned int temp1,temp2;
	temp1=2*clusterNum;
	temp2=temp1/DeviceInfo.BPB_BytesPerSec;
	temp1=temp1-temp2*DeviceInfo.BPB_BytesPerSec;
	return temp1;
}

unsigned int GetNextClusterNum(unsigned int clusterNum)
{
	unsigned int xxgFatSecNum,xxgFatEntOffset;
	
	xxgFatSecNum=ThisFatSecNum(clusterNum);
	xxgFatEntOffset=ThisFatEntOffset(clusterNum);

	if(FatSectorPointer!=xxgFatSecNum)
	{	
		
		if(!RBC_ReadOneSec(xxgFatSecNum, FATBUF))
			return 0xFFFF;
		FatSectorPointer=xxgFatSecNum;
	}
	

	///////////////////////////////////////////////////
	clusterNum=FATBUF[xxgFatEntOffset+1];
	clusterNum=clusterNum<<8;
	clusterNum+=FATBUF[xxgFatEntOffset];	
	return clusterNum;
}