makedos4g.txt

該程序可以將DOS的工作模式進行轉變,由實模式進入保護模式.想了解計算机底層的人一定會喜歡,呵呵!

#include <dos.h>

////////////////////////////////////////////////////////////////

//          4G Memory Access

//  This Program Can Access 4G Bytes in DOS Real

//Mode,Needn't in Protection Mode It Works.

//  The Program Enter 32 Bit Flat Mode a moment and

//Only Load FS a 32 Bit Flat Mode Selector,Then Return

//Real Mode.

//  Used The FS Can Access All 4G Memory till It be

//reloaded.

//          

///////////////////////////////////////////////////////////////

 

unsigned long   GDT_Table[]=

{   0,  0,                         //NULL   - 00H

0x0000FFFF, 0x00CF9A00,     //Code32 - 08H Base=0 

//Limit=4G-1 Size=4G

    0x0000FFFF, 0x00CF9200      //Data32 - 10H Base=0 

//Limit=4G-1 Size=4G

};

 

//Save The IDTR before Enter Protect Mode.

unsigned char   OldIDT[6]={0};  

 

//NULL The IDTR,IDTR's Limit=0 will disable all 

//Interrupts,include NMI.

unsigned char   pdescr_tmp[6]={0};  

 

#define KeyWait()   {while(inportb(0x64)&2);}

void        A20Enable(void)

{

        KeyWait();

        outportb(0x64,0xD1);

        KeyWait();

        outportb(0x60,0xDF);    //Enable A20 with 8042.

        KeyWait();

        outportb(0x64,0xFF);

        KeyWait();

}

 

 

void        LoadFSLimit4G(void)

{

A20Enable();                //Enable A20

    

//**************************************

    //*       Disable ints & Null IDT      *

    //**************************************

    asm {

            CLI                //Disable inerrupts

            SIDT    OldIDT      //Save OLD IDTR

            LIDT    pdescr_tmp  //Set up empty IDT.Disable any

//interrupts,

        }                   //Include NMI.

    //***************************************

    //*     Load GDTR       *

    //***************************************

    asm { 

 

//The right Code is Real,But BC++'s Linker NOT Work 

//with 32-bits Code.

        db  0x66        //32 bit Operation Prefix in 16 Bit DOS.

        MOV CX,DS   //MOV   ECX,DS

        db  0x66        //Get Data segment physical Address

        SHL CX,4        //SHL   ECX,4

        MOV word ptr pdescr_tmp[0],(3*8-1)  

        //MOV   word ptr pdescr_tmp[0],(3*8-1)

        db  0x66

        XOR AX,AX   //XOR   EAX,EAX

        MOV AX,offset GDT_Table

//MOV   AX,offset GDT_Table

        db  0x66

        ADD AX,CX   //ADD   EAX,ECX

        MOV word ptr pdescr_tmp[2],AX

                    //GDTR Base high16 bits

        db  0x66

        SHR AX,16   //SHR   EAX,16

        MOV word ptr pdescr_tmp[4],AX   

                    //GDTR Base high16 bits

        LGDT    pdescr_tmp  //Load GDTR

}

    //**************************************

    //*  Enter 32 bit Flat Protected Mode  *

    //**************************************

    //  Set CR0 Bit-0 to 1 Enter 32 Bit Protection

    //Mode,And NOT Clear machine perform cache,It Meaning

    //the after Code HAD Ready To RUN in 32 Bit Flat Mode,

    //Then Load Flat Selector to FS and Description into it's

    //Shadow register,After that,ShutDown Protection Mode

    //And ReEnter Real Mode immediately.

    //  The FS holds Base=0 Size=4G Description and

    //it can Work in Real Mode as same as Pretect Mode,

    //untill FS be reloaded.

    //  In that time All the other Segment Registers are

    //Not Changed,except FS.(They are ERROR Value holded in CPU).

    asm {

        MOV DX,0x10                 //The Data32 Selector

        db  0x66,0x0F,0x20,0xC0     //MOV   EAX,CR0

        db  0x66

        MOV BX,AX                   //MOV   EBX,EAX

        OR  AX,1

        db  0x66,0x0F,0x22,0xC0     //MOV   CR0,EAX

//Set Protection enable bit

JMP Flush

        }               //Clear machine perform cache.

    Flush:              //Now In Flat Mode,But The 

//CS is Real Mode Value.

    asm {                    //And it's attrib is 16-Bit Code 

//Segment.

        db  0x66

        MOV AX,BX           //MOV   EAX,EBX

        db  0x8E,0xE2           //MOV   FS,DX   //Load FS now

        db  0x66,0x0F,0x22,0xC0     

                        //MOV   CR0,EAX

        //Return Real Mode.Now FS's Base=0 Size=4G

        LIDT        OldIDT          

        //LIDT  OldIDT Restore IDTR

        STI                 //STI       Enable INTR

        }

}

//With FS can Access All 4G Memory Now.But if FS be reloaded 

//in Real Mode It's Limit will Be Set to FFFFh(Size=64K),

//then Can not used it

// to Access 4G bytes Memory Again,Because FS is Segment:Offset

//Memory type after that.

//If Use it to Access large than 64K will generate Execption 0D.

//unsigned char ReadByte(unsigned long Address)

{

    asm db  0x66

    asm mov di,word ptr Address //MOV   EDI,Address

    asm db  0x67                    //32 bit Address Prefix

    asm db  0x64                    //FS:

    asm mov al,byte ptr [BX]        //=MOV AL,FS:[EDI]

    return  _AL;

}

unsigned char   WriteByte(unsigned long Address)

{

    asm db  0x66

    asm mov di,word ptr Address //MOV   EDI,Address

    asm db  0x67                    //32 bit Address Prefix

    asm db  0x64                    //FS:

    asm mov byte ptr [BX],al        //=MOV FS:[EDI],AL

    return  _AL;

}

///////////////// Don't Touch Above Code /////////////

#include <stdio.h>

/////////////////////////////////////////////////////////////

//ゴ