;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;Copyrights(C) 2005, 2006 by Sohail Qayum Malik<sohail@stupidcomputing.com>;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;bootblok.asm(The boot-sector code).                                       ;;
;;Written by, Sohail Qayum Malik<sohail@stupidcomputing.com>                ;;
;;                                                                          ;;
;;DL    = drive-id of the device we booted from.                            ;;
;;DH    = head-number of the device we booted from.                         ;;
;;ES:SI = in case of HD boot the segmented address of the partition table's ;;
;;        active partition table entry.                                     ;;
;;                                                                          ;;
;;This programm will load the secondry boot code at 0x1000:0000.            ;;
;;The secondry boot programm will transfer it self high, then execution     ;;
;;will be in the high memory area.                                          ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


SPOFFSET                        equ             7c00h
;LOADOFFSET                      equ             7c3eh


SECTORSSEGMENT                  equ             0000h
SECTORSOFFSET                   equ             7e00h

KERNELSEGMENT                   equ             1000h
KERNELOFFSET                    equ             0000h
;KERNELOFFSET1                   equ             0100h


;KERNELSEGMENT                   equ             0ffffh
;KERNELOFFSET                    equ             00010h



CR                              equ             0dh
LF                              equ             0ah
EOL                             equ             00h


;Okhey we are at 0000:7c00, the first 62 bytes are the DOS specific bytes
;so our code starts at the following location counter.
org     7c3eh


        ;Jump to the _start
        jmp             _start                  

;DATA

logo            db      CR,LF,'Booting YAN....',EOL
MHLT            db      CR,LF,CR,LF,'System halted.',EOL
KSR             db      CR,LF,"Secondry boot loader's sector ID's read.",EOL
KCR             db      CR,LF,'Loading secondry boot loader low.',CR,LF,EOL
shit            db      '*',EOL
MA20            db      CR,LF,'A20 line enabled.',EOL

rderr           db      CR,LF,"Read error ",EOL
errno           db      "00 ",EOL


_enableA20:
        pusha
        cli
        mov     cx, 05h
        _attempt:
                call    _commandwait
                mov     al, 0d0h
                out     64h, al

                call    _datawait
                xor     ax, ax
                in      al, 60h
                push    ax

                call    _commandwait
                mov     al, 0d1h
                out     64h, al

                call    _commandwait
                pop     ax
                or      al, 00000010b
                out     60h, al

                call    _commandwait
                mov     al, 0d0h
                out     64h, al

                call    _datawait
                xor     ax, ax
                in      al, 60h
                bt      ax, 1
                jc      _success
                loop    _attempt
                jmp     _fail
                retn

        _success:
                sti
                popa
                xor     ax, ax
                mov     si, MA20
                call    _print
                retn

        _fail:
                jmp    _badKarma

;See if 8042 is ready for command at port 64h or data at 60h.
_commandwait:
        xor     ax, ax
        in      al, 64h
        bt      ax, 1
        jc      _commandwait
        retn

;See if 8042 has data for us.
_datawait
        xor     ax, ax
        in      al, 64h
        bt      ax, 0
        jnc     _datawait
        retn



_error:
        mov     si, errno + 1
        prnum:        
                mov     al, ah
                and     al, 0fh
                cmp     al, 0ah
                jb      digit
                add     al, 07h
        digit:
                add     [si], al
                dec     si
                mov     cl, 04h
                shr     ah, cl
                jnz     prnum
        retn

_print   :

        lodsb
        or              al, al
        jz              _stop
        mov             ah, 0eh
        mov             bx, 0007h
        int             10h
        ;Jump to _print
        jmp             _print


_stop:        
        retn


_start:

        cli
        xor             ax, ax
        mov             ss, ax
        mov             ds, ax
        mov             sp, SPOFFSET    
        sti

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
        ;Lets save the registers that were set before us.
        push            es
        push            si
        push            dx
        mov             bp, sp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
        
        ;The booting message.
        mov             si, logo                ;The logo.
        call            near    _print          ;call _print

        call            _enableA20

        ;Lets load the sector ID's of the kernel file.
        mov             ax, SECTORSSEGMENT
        mov             es, ax
        mov             bx, SECTORSOFFSET
        mov             ah, 02h                 ;Service number.
        mov             al, 01h                 ;Number of sectors to read.
        mov             ch, 00h                 ;Track number.
        mov             cl, 02h                 ;Starting sector number.
        mov             dh, 00h                 ;Head number.
        int             13h
        jc              _handleErrors
        mov             si, KSR
        call            near    _print

        ;Lets load the kernel.
        mov             si, KCR
        call            near    _print
        ;Load the sector count.
        mov             cx, [_seclow]
        mov             si, SECTORSOFFSET       
        mov             ax, KERNELSEGMENT
        mov             es, ax
        mov             bx, KERNELOFFSET
;        mov             bx, KERNELOFFSET1


_loadKernel:
                push    cx
                mov     ah, 02h
                mov     al, 01h
                mov     cx, [si]
                mov     dh, [si + 02h]
                int     13h
                jc      _handleErrors
                pop     cx
                add     si, 03h
                add     bx, 0200h
                push    bx
                push    si
                mov     si, shit
                call    near    _print
                pop     si
                pop     bx
        loop            _loadKernel

        pop             dx
        pop             si
        pop             es

        mov             ax, KERNELSEGMENT
        mov             ds, ax


;        db      0eah, 10h, 00h, 0ffh, 0ffh        
;_humps:        
        db      0eah, 00h, 00h, 00h, 10h
;        db       0eah, 00h, 01h, 00h, 10h
;        db      0eah, 00h, 00h, 00h, 10h

_handleErrors:
;        push    si
        call    near    _error
        mov     si, rderr
        call    near    _print
        mov     si, errno
        call    near    _print
;        pop     si
        

        ;We should not reach this area, if we do then print the message and halt.
_badKarma:   
        mov             si, MHLT
        call            near    _print
_hold:

        hlt
        jmp             _hold


;More Data.
;Total number of sectors to be read from the following sectors.
;This value should be orgin at 1 to max.
_seclow         dw      0002h