;
; 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