comment % support file for putting the CPU into flat real mode support file for gate A20 switching % ;---------------------------------------------------------------------------- ; MASSiVE Flat Real mode routines ; (Version 1.0B) ; by ; NiX/MASSiVE ; Butterfly/MASSiVE ; ; You may use this sourcecode for free, we don't accept anything in return. ; But we would really like it if you greet us, or send your newest productions ; to us. ; ; This is a beta version, only providing you with the essential routines and ; some examples, just real plain flat-real-mode. More special things will be ; available in a next version. ; ; Read the DOC for more information. .386P ; 386 Code ofcourse... ;--------------------------------------------------------------------------- ; Descriptors and stuff used for setting up FRM mem32_GDT dw 4 dup(0) Code16GDT = 8 dw 0ffffh,0ffh,9a00h,0 Data16GDT = 16 dw 0ffffh,0ffh,9200h,0 Data32GDT = 24 dw 0ffffh,0ffh,9200h,8fh GDTptr label fword dw offset GDTptr-1-offset Mem32_GDT dd offset Mem32_GDT ; Absolute adress GDTtable dw 0 ;------------------------------------------------------------------------- ; This routine sets DS, ES, FS and GS to a 4Gigabyte limit. ; To do this it swaps to PM for a little while, this is not possible in V86 ; mode. If computer is in V86 mode the carry will be set on return, and you ; are still in RM. ; Crashes segment registers!!! Set4Gig: mov eax,cr0 ; Check for V86 mode ror eax,1 ; jc flat_error ; If carry set get out of here. mov ax,cs ; Set up GDT for this code segment mov ds,ax movzx eax,ax shl eax,4 add dword ptr ds:GDTptr+2,eax lgdt fword ptr ds:GDTptr mov ax,cs and eax,65535 shl eax,4 mov word ptr ds:Mem32_GDT[Code16GDT+2],ax mov word ptr ds:Mem32_GDT[Data16GDT+2],ax ror eax,16 mov byte ptr ds:Mem32_GDT[Code16GDT+4],al mov byte ptr ds:Mem32_GDT[Data16GDT+4],al mov byte ptr ds:Mem32_GDT[Code16GDT+7],ah mov byte ptr ds:Mem32_GDT[Data16GDT+7],ah cli ; No ints ; Beam us to PMODE!! mov eax,cr0 or al,1 mov cr0,eax db 0eah ; Far jump to PMODE label dw offset Pmode dw Code16GDT ; We're in PMODE!! Pmode: mov ax,Data32GDT ;mov ds,ax ; Set them all to 4Gig ;mov es,ax ;leave ES and DS alone, cuz old 8088 programs mov fs,ax ;may rely on old memory wrapping techniques! mov gs,ax ; Beaming out! mov eax,cr0 and al,0feh mov cr0,eax db 0eah ; Far jump to Rmode label. dw offset Rmode dw Code ; Back in the real world! Rmode: clc ; No carry, everything went OK sti ; Ints Back on. mov ax,cs ; set CS=DS mov ds,ax xor ax,ax ; Set segment register to 0 mov gs,ax ; Leave4Gig: ret flat_error: push cs pop ds mov dx,offset V86Mess mov ah,9 int 21h mov ax,4c03h ; errorlevel 3=v86mode int 21h V86mess db "Error: V86 Mode present!",CR,LF,"$" ;----------------------------------------------------------------------------- ; Enables the A20 adress line. This is needed to adress the memory above 1Mb. ; Do this at the start of your program and everytime another program has been ; active. In an interrupt routine this means you should do it everytime the ; routine is being called, don't worry, it doesn't takes much time. EnableA20: mov al,0D1h out 64h, al call A20wait mov al,0DFh out 60h, al call A20wait mov al,0FFh out 64h,al call A20wait ret A20Wait: in al,64h jmp $+2 and al,2 jnz A20wait ret ;copies 0:0->512k to 2mb area. define this address via declaration!! ;eax, ecx, esi, edi are destroyed. put512high proc near mov ecx, (512*1024) / 4 mov edi, DOS_START ; copy to 2mb xor esi, esi cli copyhloop: mov eax, gs:[esi] mov gs:[edi], eax add edi, 4 add esi, 4 loop copyhloop ; save SS:SP mov ax, sp shl eax, 16 mov ax, ss mov gs:[edi], eax add edi, 4 mov gs:[edi], bp sti ret put512high endp ;copies 0:0->512k to 2mb area. define this address via declaration!! ;eax, ecx, esi, edi are destroyed. put512low proc near mov ecx, (512*1024) / 4 mov esi, DOS_START ; copy to 2mb xor edi, edi cli copylloop: mov eax, gs:[esi] mov gs:[edi], eax add esi, 4 add edi, 4 loop copylloop sti ret put512low endp ;--------------------------------------------------------------------------- ;swaps 0:0->512 with 2mb area ;kills all upper 16 bits of all registers. _swap512k macro local swaploop shl eax, 16 ; save ax shl ebx, 16 ; save bx shl edx, 16 ; save dx mov dx, cx ; save cx shl ebp, 16 ; save bp mov bp, si ; save si mov fs, di ; save di (fs is never used) mov ecx, (512*1024) / 2 mov edi, DOS_START xor esi, esi cli swaploop: mov ax, gs:[esi] mov bx, gs:[edi] mov gs:[edi], ax mov gs:[esi], bx add edi, 2 add esi, 2 loop swaploop mov di, fs ; restore di mov si, bp ; restore si shr ebp, 16 ; restore bp mov cx, dx ; restore cx shr edx, 16 ; restore dx shr ebx, 16 ; restore bx shr eax, 16 ; restore ax sti endm ;---------------------------- ;check_himem ;checks if himem.sys is loaded, abort with error message if so. ; ; check_himem proc near mov ax, 4300h ; installation check int 2fh ; al=80h if installed. cmp al, 80h jz himemerr ret himemerr: push cs pop ds mov dx,offset himemerrmsg mov ah, 9 int 21h mov ax, 4c02h ; errorlevel 2=himem int 21h himemerrmsg db "Error: This program does not work with Himem.sys " db "installed.",CR,LF,"Boot clean and try again!",CR,LF,"$" check_himem endp ;-------------------------------------------------------------------------- check_2mb proc near mov ax, 8800h int 15h ; returns extended size in k cmp ax, 1*1024 ; requires 1mb extended mem jb mem_error ret mem_error: push cs pop ds mov dx,offset need2mbmsg mov ah, 9 int 21h mov ax, 4c04h ; errorlevel 4=memsize int 21h need2mbmsg db "Error: This program requiresd at least 2mb.",CR,LF,"$" check_2mb endp ;-------------------------------------------------------------------------- ;tweak reported memory size to 512k instead of 640 change_base_size proc near mov word ptr gs:[413h],512 ret change_base_size endp