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A few notes about my code:
1) This is just a tester, so it's not that efficient.
2) I'm using DEBUG.EXE to compile this, hence the hard-coded addresses.
3) Because I'm hard-coding addresses, you'll see a lot of NOP padding so that if I change the program later it won't be such a pain to go through the entire program and changing all the addresses manually.
4) This program sets A20 and then checks to see how much memory is present in the system. I know Windows will block it at some point, but at least it will work in a sense.
jmp 01f0 ; ;DATA ;0103 - MEMSTATUS (0:continue, 1:stop) db 0 ;0104 - EnableAddrLine db "Enabling A20 Line...$" ;0119 - OK db "OK",0d,0a,"$" ;011E - Error db "ERROR!$" ;0125 - Memory db "Total Memory:$" ;0133 - KB db "KB$" ;0136 - Press any key db 0d,0a,"Press any key...$" nop ;014A - Text buffer, 16 chars db "$$$$$$$$$$$$$$$$" ;015A - Waiting for command ready db 0d,0a,"Waiting for controller ready signal...$" ;0183 - Waiting for data db 0d,0a,"Waiting for controller to return data...$" ;01AE - RESERVED FOR EXPANSION db "#RESERVED#" ; ;END OF DATA - 01B7 ; ;-------------------------------------------------- ;VOID INTTOASCII(DWORD) @ 01B8 ;dumps decimal representation of DWORD to buffer ;-------------------------------------------------- ;EAX = number to convert db 66 pop ax ;EDX = 0, carries the modulus db 66 xor dx,dx ;set [BX] to point to end of buffer mov bx,0158 ;set ECX = 0ah, force DIV into 32-bit mode db 66 mov cx,000a dw 0000 ;01C6 - div loop db 66 div cx ;edx contains remainder, we're interested in DL ;convert num to char, works only in bases <= 10 add dl,30 ;store char in buffer mov [bx],dl ;point to previous char in buffer dec bx ;is EAX = 0? db 66 or ax,ax jnz 01c6 ;we're done, EAX = 0. ;01D4 - fill rest of buffer with spaces. cmp bx,014a jz 01df mov byte ptr [bx],20 jmp 01d4 ;01DC - return ret ; ; ;-------------------------------------------------- ;VOID GPFAULTHANDLE(VOID) @ 01E0 ;-------------------------------------------------- mov byte ptr [0103],1 iret nop nop nop nop nop nop nop nop nop nop ; ; ;--------------------------------------------------- ;VOID MAIN(VOID) @ 01F0 ;--------------------------------------------------- ;print loading string mov ah,09 mov dx,0104 int 21h ;;;;;;print wait for ready message mov ah,09 mov dx,015a int 21h nop ;disable interrupts cli ;0200 - wait for controller to be ready for input xor ax,ax in al,64 and ax,2 jz 0200 ;controller is ready. send read status command mov al,0d out 64,al ;;;;;;print wait for data message sti mov ah,09 mov dx,0183 int 21h cli nop nop ;0218 - wait for controller output xor ax,ax in al,64 and ax,1 jz 0218 ;controller is ready. read status xor ax,ax in al,60 ;save status on stack push ax ;;;;;;print wait for ready message sti mov ah,09 mov dx,015a int 21h cli nop ;0230 - wait for controller to be ready for input xor ax,ax in al,64 and ax,2 jz 0230 ;controller is ready. send write status command mov al,d1 out 64,al ;;;;;;print wait for data message sti mov ah,09 mov dx,0183 int 21h cli nop nop ;0248 - wait for controller output xor ax,ax in al,64 and ax,1 jz 0248 ;controller is ready, set A20 enable bit and write pop ax or al,2 out 60,al ;check to see if it was set - read back status. ;;;;;;print wait for ready message sti mov ah,09 mov dx,015a int 21h cli ;0260 - wait for controller to be ready for input xor ax,ax in al,64 and ax,2 jz 0260 ;controller is ready. send read status command. mov al,0d out 64,al ;;;;;;print wait for data message sti mov ah,09 mov dx,0183 int 21h cli nop nop ;0278 - wait for controller output xor ax,ax in al,64 and ax,1 jz 0278 ;controller is ready. read status. xor ax,ax in al,60 ;check to see if A20 is enabled and al,2 jnz 02a0 ; ;0289 ;error occurred. print and quit. ;print error message. sti mov ah,09 mov dx,011e int 21h ;print press any key message mov dx,0136 int 21h ;pause mov ah,00 int 16h ;exit mov ax,4cff int 21h nop ; ;02A0 ;no error occurred. ;print OK message. sti mov ah,09 mov dx,0119 int 21h ;do memcheck. ;hook general protection fault interrupt 0dh ;get original interrupt vector ;returned in ES:BX mov ax,350d int 21h ;save to stack push bx push es ;reset vector to handler at DS:01E0 mov ax,250d mov dx,01e0 int 21h ;begin memcheck db 66 xor bx,bx nop nop nop nop nop nop ;02C0 - memcheck loop cmp byte ptr [0103],1 jz 02ce db 67 mov dl,[bx] db 66 inc bx jmp 02c0 ;02CE - end memcheck loop ;divide by 1024 to get KB mov cl,0a db 66 shr bx,cl ;get decimal string of memory size db 66 push bx call 01b8 ;print memory size string mov ah,09 mov dx,0125 int 21h ;print decimal number representing memory size mov dx,014a int 21h ;print KB string mov dx,0133 int 21h ;pause mov ah,00 int 16h ;reset old interrupt vector pop dx pop ds mov ax,250d int 21h ;exit mov ax,4c00 int 21h ;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;end of program at 02F9 nop nop nop nop nop nop nop nop ;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;padded so it's exactly 0x200 ;bytes long.
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