;=----------------------------------------------------------------------------=;
;                          GNU GPL OS/K                                        ;
;                                                                              ;
;   Authors: spectral`                                                         ;
;            NeoX                                                              ;
;                                                                              ;
;   Desc:   Master Boot Record for OS/K                                        ;
;                   (x86_64 architecture only)                                 ;
;=----------------------------------------------------------------------------=;


[BITS 16]                           ; real mode
[ORG 0x7C00]                        ; address where the BIOS/UEFI CSM is loading us

    jmp 0x0000:Start                ; far-jump to avoid loading address issues with older BIOSes
                                        ;   some older BIOSes could load bootloader.bin at 0x7C00:0x0000
                                        ;   while newer ones would load it at 0x0000:0x7C00...
                                        ;   here the far-jump sets CS to 0

bootdb  db     'GNUOS/K '                ;Fabricant + n°série Formatage
sizec   dw      512                      ;octet/secteur
db      1                        ;secteur/cluster
reserv  dw      1                        ;secteur reserv‚
nbfat   db      2                        ;nb de copie de la FAT
nbfit   dw      224                      ;taille rep racine
allclu  dw      2880                     ;nb secteur du volume si < 32 még
db      0F0h                     ;Descripteur de média
fatsize dw      9                        ;secteur/FAT
nbtrack dw      18                       ;secteur/piste       
head    dw      2                        ;nb de tˆteb de lecture/écriture
hidden  dd      0                        ;nombre de secteur cach‚s
dd      0                        ;si nbsecteur = 0 nbsect                                       ; the number of sectors
bootdrv db      0                        ;Lecteur de d‚marrage
bootsig db      0                        ;NA
db      29h                      ;boot signature 29h
bootsig2 dd     01020304h                ;no de serie
pope    db      'COS2000    '            ;nom de volume
db      'FAT12   '               ;FAT
				
;; DATA
Bootdrv     db  0x00
Starting    db  0x0A, 0x0D, 0x07, " GNU GPL OS/K ", 0x0A, 0x0D, 0x0A, 0x0D, 0
NoLongMode  db  0x0A, 0x0D, "ERROR: Your computer is not designed for x64 OS", 0
A20ERR      db  0x0A, 0x0D, "ERROR: Failed to enable A20 line!", 0
SwErr       db  0x0A, 0x0D, "ERROR: Loading failed!", 0
Init        db  0x09, " Checking CPUID", 0
EnA20       db  0x09, " Enabling A20 line", 0
Switch      db  0x09, " Loading Second Stage", 0
Pass        db  " OK", 0x0A, 0x0D, 0

%define SECOND_STAGE 0x100
;; INCLUDES
%include "boot/mbr.inc"             ; for Is64Bits
%include "boot/common.inc"          ; for PrintB

Start:   
    pushad
    pushfd
    pushf
    mov [Bootdrv], dl               ; dl contains the boot drive. Saving it.
        
    ;; hello world
    push si
    mov si, Starting
    call PrintB
    
    ;; compatibility check
    mov si, Init
    call PrintB
    pop si
     
    call Is64bits                   ; in mbr.inc
    jc ErrorNo64
    
    push si 
    mov si, Pass
    call PrintB
    
    ;; enabling A20
    mov si, EnA20
    call PrintB
    pop si 
    
    in al, 0x92
    or al, 2
    out 0x92, al
    jc A20Fail
    
    push si 
    mov si, Pass
    call PrintB
    
    
    ;; switch to second stage
    mov si, Switch
    call PrintB
    pop si
    ;; Reset floppy drive and load second stage
    call LoadSec                    ; Loading from boot disk
    jc SwFail
            
    popf
    popfd
    popad
    mov ax, [Bootdrv]
    push ax 
    jmp dword SECOND_STAGE:0000           ; Jumping to second stage loader.
    ;;END OF MBR

;;----------------------------------------------------------------------------;;
A20Fail:
    mov si, A20ERR
    call PrintB
    jmp Die
SwFail:
    mov si, SwErr
    call PrintB
    jmp Die
ErrorNo64:
    mov si, NoLongMode
    call PrintB
Die:
    cli
    hlt                             ; die nooooow
    jmp Die
End:
    times 510-($-$$) db 144         ; NOP until 510
    dw 0xAA55                       ; magic word