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flat assembler > OS Construction > cpm-86 in 32 bit protected mode to 64 bit real mode

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connor



Joined: 07 Jun 2016
Posts: 38
Location: sj ca
USING THE FOLLOWING CODE BELOW, How would i add 64 bit real mode?

Code:
;
; P-MODE Version 0.0
; Demonstration Of 32-Bit Protected Mode Under 'CP/M-86 For The IBM'
; Freeware from Kirk Lawrence
;
;     To assemble:   ASM86 P-MODE $ SZ PZ
;                   GENCMD P-MODE
;
cseg                                    ;start of code segment
        org     100h                    ;leave room for base page
        jmp     start                   ;go start the program
;
cpu_err db      13,10,'P-MODE Version 0.0'
        db      13,10,'Freeware from Kirk Lawrence'
        db      13,10,10,'-> Sorry, a 386 or higher processor is required.'
        db      13,10,07,'$'
vid_adr dw      0B800h
cls     db      27,'n',27,'E$'
bottom  db      27,'Y',54,32,27,'m$'
msg1    db      '    Greetings from Protected Mode!    '
msg2    db      ' Press any key to return to Real Mode '
;
; Make sure we have a 386 or higher processor.
;
start:
        pushf                           ;save flags
        xor     ah,ah                   ;clear high byte
        push    ax                      ;push AX onto the stack
        popf                            ;pop this value into the flag register
        pushf                           ;push flags onto the stack    
        pop     ax                      ;...and get flags into AX
        and     ah,0F0h                 ;try to set the high nibble
        cmp     ah,0F0h                 ;the high nibble is never 0F0h on a
        je      no_386                  ;80386! 
        mov     ah,70h                  ;now try to set NTIOPL    
        push    ax
        popf
        pushf
        pop     ax
        and     ah,70h                  ;if they couldn't be modified, there
        jz      no_386                  ;is no 80386 installed
        popf                            ;restore the flags
;
; Check for TTL monochrome video.  If found, set the appropriate address.
;
        int     11h                     ;call BIOS equipment check
        and     ax,30h                  ;test the return in AX
        cmp     ax,30h                  ;do we have TTL monochrome video?
        jne     clr_sc                  ;no, so assume color
        mov     vid_adr,0B000h          ;set monochrome video address
;
; Clear the screen.
;
clr_sc:
        mov     dx,offset cls           ;point DX to 'clear screen' sequence
        call    prt_str                 ;print it
;
; Set the Extra Segment to the video address.
;
        mov     ax,vid_adr
        mov     es,ax
;
; Enter protected mode.
;
        cli                             ;interrupts off
        db      00Fh, 020h, 0C0h        ;mov eax,cr0
        db      00Ch, 001h              ;or al,1
        db      00Fh, 022h, 0C0h        ;mov cr0,eax
;
; We're now in protected mode.  Print a message to the screen.
;
        mov     bx,1646                 ;set screen location in BX
        mov     si,offset msg1          ;point SI to the screen message
        mov     cx,38                   ;set counter CX to length of scrn msg
        mov     ah,95                   ;screen attribute in AH
        call    put_2_scrn              ;go write to video memory
;
        mov     bx,1966                 ;set screen location in BX
        mov     si,offset msg2          ;point SI to the screen message
        mov     cx,38                   ;set counter CX to length of scrn msg
        mov     ah,14                   ;screen attribute in AH
        call    put_2_scrn              ;go write to video memory
;
; Wait for user keypress.
;
get_key:
        mov     dx,60h
        in      al,dx
        shl     al,1
        jc      get_key
;
; Return to real mode.
;
        db      024h, 0FEh              ;or al,not 1
        db      00Fh, 022h, 0C0h        ;mov eax,cr0
        sti                             ;interrupts on
;
; Place the cursor at the bottom of the screen and exit.
;
        mov     dx,offset bottom        ;point DX to the positioning sequence
        call    prt_str                 ;print it
exit:
        xor     cx,cx                   ;function 0 - reset system
        int     224                     ;call BDOS services
;
; Processor error-handling routine.
;
no_386:
        mov     dx,offset cpu_err       ;point to CPU error message
        call    prt_str                 ;print it
        jmp     exit                    ;go exit
;
; Routine to write a text string directly to video memory.
;
; Input:  AH = screen attribute
;         BX = physical location on the screen
;         CX = loop counter value
;         SI = start of text string
;
put_2_scrn:
        lodsb                           ;load a byte of the message into AL 
        mov     es: byte ptr [bx],al    ;move it to the screen
        inc     bx                      ;increment BX
        mov     es: byte ptr [bx],ah    ;move attribute to the screen
        inc     bx                      ;increment BX
        loop    put_2_scrn              ;repeat if CX > 0
        ret                             ;return
;
; Print string routine.
;
prt_str:
        mov     cl,9                    ;function 9 - print string
        int     224                     ;call BDOS services
        ret                             ;return
end    
Edit by revolution: Added code tags

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Post 25 Jun 2018, 03:49
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 15984
Location: Qo'noS
I'm not sure that 64 bit real mode is a thing. In long mode you have to enable paging and set up a page table. The CPU enforces this.
Post 25 Jun 2018, 12:07
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CandyMan



Joined: 04 Sep 2009
Posts: 284
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop
where you define GDT and IDT?
Post 25 Jun 2018, 17:00
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connor



Joined: 07 Jun 2016
Posts: 38
Location: sj ca
i don't know what a page table, GDT or IDT is

all I want is some ideas and brainstorming.

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Post 26 Jun 2018, 04:05
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CandyMan



Joined: 04 Sep 2009
Posts: 284
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop
protected mode is not the same like real mode. you must define segment descriptors in Global Descriptor Table (GDT) and interupts and exceptions in Interrupt Descriptor Table (IDT). without it your program will be suspended or a computer will reset. additionally one should check (smsw instruction) whether we are in the real mode or can already in virtual. in long mode a paging is necessary.
that's all it isn't so difficult, a little reading documentation requires.
see also:
https://patater.com/gbaguy/x86asm.htm
http://www.cs.virginia.edu/~evans/cs216/guides/x86.html
https://wiki.osdev.org/GDT_Tutorial
http://prodebug.sourceforge.net/pmtut.html
https://www.codeproject.com/Articles/45788/The-Real-Protected-Long-mode-assembly-tutorial-for
Post 26 Jun 2018, 08:28
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