boot2.asm

Jazmyn is a 32-bit, protected mode, multitasking OS which runs on i386 & above CPU`s. Its complete

;******************     Second stage boot loader      ***********************

.386p           ;we have a 386

code_seg segment use16
assume cs:code_seg

jmp start

        DESC struc                                      ;descriptor structure
                L15_L0    dw 0                          ;limit 15...0
                B15_B0    dw 0                          ;base 15...0
                B23_B16   db 0                          ;base 23...16
                ACCESS    db 0                          ;P,DPL,DT,DATA|CODE,EXPAND-DOWN|CONFIRMING,W|R,A
                LIM_FLAGS db 0                          ;G,DEF|BIG,RES,AV,limit 19...16
                B31_B24   db 0                          ;base 31...24
        DESC ends

        DESC0 DESC <0,0,0,0,0,0>                        ;dummy descriptor
        DESC1 DESC <0ffffh,0000h,00h,9ah,0cfh,00h>      ;flat code
        DESC2 DESC <0ffffh,0000h,00h,92h,0cfh,00h>      ;flat data
        DESC3 DESC <0ffffh,2000h,00h,9ah,0cfh,00h>      ;kernel code     
        DESC4 DESC <007ffh,1000h,00h,92h,040h,00h>      ;IDT memory
        DESC5 DESC <0ffffh,0C000h,09h,9ah,0cfh,00h>     ;load.com code

        GDT_LIMIT dw $-DESC0-1

        a20failed       db      'A-20 enabling failed!',13,10,0
        rebootmsg       db      13,10,'Press any key to reboot',13,10,0
        KERNEL_SECTORS  equ     81
        KERNEL_BASE     equ     200h
        sect_to_read    dw      18
        head            db      ?
        track           db      ?

        gdt_lim dw ?
        gdt_bse dd 00001800h

display proc near
prnt:
        lodsb
        or      al,al
        jz      over
        mov     ah,0eh
        mov     bx,0007
        int     10h
        jmp     prnt
over:
        ret
display endp

key macro
        mov     ah,0
        int     16h
endm

wait_for_buf_empty proc near
wait_empty:
        in      al,64h                                  ;test 1st bit of status port
        test    al,2                                    ;input reg has data for 8042
        jnz     wait_empty
        ret
wait_for_buf_empty endp


wait_for_data proc near
wait_data:                                              ;test 0th bit of status port
        in      al,64h
        test    al,1
        jz      wait_data
        ret
wait_for_data endp

enable_a20 proc near
        call    wait_for_buf_empty
        mov     al,0d0h                                 ;read output port--the output reg should be
        out     64h,al                                  ;empty. we get data in 0x60
        call    wait_for_data
        xor     ax,ax
        in      al,60h
        push    ax                                      ;save output port
        call    wait_for_buf_empty
        mov     al,0d1h                                 ;write to output port
        out     64h,al                                  ;next byte written to 0x60 goes to  o/p port
        call    wait_for_buf_empty
        pop     ax
        or      al,00000010b                            ;set 1st bit -- A-20 gate
        out     60h,al
        call    wait_for_buf_empty
        mov     al,0d0h                                 ;read o/p port
        out     64h,al
        call    wait_for_data
        in      al,60h                                  ;test for 1st bit (A-20 enabled?)
        test    al,2
        jz      failure
        mov     al,1                                    ;al=1 success
        jmp     a20over
failure:
        mov     al,0                                    ;al=0 failure
a20over:
        ret
enable_a20 endp

make32 macro seg,off
        mov     eax,0
        mov     ebx,0
        mov     ax,seg
        mov     bx,off
        shl     eax,4
        add     eax,ebx
endm

init_pic proc near
        ;0th bit-icw4 required,4th bit clr-Edge triggering
        ;with edge-trigger,IRQ is indicated by transition
        ;of signal from low to high(standard).

        mov     al,00010001b
        out     20h,al                                  ;icw1 master
        out     0a0h,al                                 ;icw1 slave
        mov     dx,21h

        mov     al,018h                                 ;master PIC -> 0x18 - 0x1F (24 - 31)
        out     dx,al                                   ;icw2 parent

        mov     al,020h                                 ;slave PIC -> 0x20 - 0x27  (32 - 39)
        out     0a1h,al                                 ;icw2 slave

        mov     al,0100b
        out     dx,al                                   ;icw3 master,IRQ2 is connected to slave
        mov     al,2
        out     0a1h,al                                 ;icw3 slave,master IRQ to which slave is connected
        mov     al,1                                    ;0th bit-8086 mode
        out     dx,al                                   ;icw4 master
        out     0a1h,al                                 ;icw4 slave
        mov     al,011111011b 
        out     dx,al                                   ;ocw1 master,mask IRQ0-IRQ7 except IRQ2
        or      al,0100b
        out     0a1h,al                                 ;ocw1 slave,MASK IRQ8-IRQ15
        ret
init_pic endp

diskmotoroff proc near
        mov     dx,03f2h                                ;Digital Output Register
        in      al,dx
        and     al,0fh                                  ;clear motor-on bits
        out     dx,al                                   ;output to DOR
        ret
diskmotoroff endp

dispnum macro a
        mov     al,a
        mov     ah,0eh
        mov     bx,0007
        int     10h
endm

disph proc near
        mov     cl,4
        mov     ch,8
disph1:
        rol     eax,cl
        push    eax
        and     al,0fh
        add     al,30h
        cmp     al,'9'
        jbe     disph2
        add     al,7
disph2:
        dispnum al
        pop     eax
        dec     ch
        jnz     disph1
        ret
disph endp
        
set_gdt proc near
        mov     si,offset DESC0
        mov     ax,180h
        mov     es,ax
        mov     di,0
        mov     ax,GDT_LIMIT
        inc     ax
        mov     cx,ax
        cld                                             ;increment si & di
        rep     movsb                                   ;move string from ds:si to es:di,times-cx
        mov     ax,GDT_LIMIT
        mov     gdt_lim,ax
        ret
set_gdt endp

start:
        push    cs
        pop     ds                                      ;initialize ds
        cli                                             ;setup stack
        mov     ax,5000h
        mov     ss,ax
        mov     sp,0ffffh
        sti


;        call    diskmotoroff                            ;BIOS does not turn off motor in pmode
        in      al,070h                                 ;Mask NMI, this is necessary before moving to protected mode
        or      al,080h
        out     070h,al
        cli
        call    enable_a20                              ;enable A-20       
        .if al == 0
                mov     si,offset a20failed
                call    display
                mov     si,offset rebootmsg
                call    display
                key
                jmp     last
        .endif
        call    init_pic                                ;initialize PIC
        call    set_gdt
        lgdt    fword ptr gdt_lim                       ;load GDTR
        mov     eax,cr0
        or      al,1
        mov     cr0,eax                                 ;set pmode bit of cr0

        mov     ax,010h
        mov     ds,ax
        mov     es,ax
        mov     fs,ax
        mov     gs,ax
        mov     ss,ax
        mov     esp,9ffffh

	db	0eah
        dw      0000h
        dw      028h
last:
        db      0eah                                    ;if something goes wrong, reboot
        dw      0000h
        dw      0ffffh

        org     512                                    ;span one complete track
code_seg ends
end