_OS _code_

[bits 16]           ; tell assembler that working in real mode(16 bit mode)
[org 0x7c00]        ; organize from 0x7C00 memory location where BIOS will load us

start:              ; start label from where our code starts

    xor ax,ax           ; set ax register to 0
    mov ds,ax           ; set data segment(ds) to 0
    mov es,ax           ; set extra segment(es) to 0
    mov bx,0x8000

    mov ax,0x13         ;clears the screen
    int 0x10            ;call bios video interrupt

    mov ah,02           ;clear the screen with big font
    int 0x10            ;interrupt display

    ;set cursor to specific position on screen
    mov ah,0x02         ; set value for change to cursor position
    mov bh,0x00         ; page
    mov dh,0x06         ; y cordinate/row
    mov dl,0x09         ; x cordinate/col
    int 0x10

    mov si, start_os_intro              ; point start_os_intro string to source index
    call _print_DiffColor_String        ; call print different color string function

    ;set cursor to specific position on screen
    mov ah,0x02
    mov bh,0x00
    mov dh,0x10
    mov dl,0x06
    int 0x10

    mov si,press_key                    ; point press_key string to source index
    call _print_GreenColor_String       ; call print green color string function

    mov ax,0x00         ; get keyboard input
    int 0x16            ; interrupt for hold & read input

    ;/////////////////////////////////////////////////////////////
    ; load second sector into memory

    mov ah, 0x02                    ; load second stage to memory
    mov al, 1                       ; numbers of sectors to read into memory
    mov dl, 0x80                    ; sector read from fixed/usb disk
    mov ch, 0                       ; cylinder number
    mov dh, 0                       ; head number
    mov cl, 2                       ; sector number
    mov bx, _OS_Stage_2             ; load into es:bx segment :offset of buffer
    int 0x13                        ; disk I/O interrupt

    jmp _OS_Stage_2                 ; jump to second stage


    ;/////////////////////////////////////////////////////////////
    ; declaring string datas here
    start_os_intro db 'Welcome to My OS!',0
    press_key db '>>>> Press any key <<<<',0

    login_username db 'Username : ',0
    login_password db 'Password : ',0

    display_text db '! Welcome to my Operating System !', 0

    os_info db 10, 'My Operating System, 16-Bit, version=1.0.0',13,0

    press_key_2 db 10,'Press any key to go to graphics view',0

    window_text db 10,'Graphics in OS......', 0
    hello_world_text db 10,10, '    Hello World!',0
    login_label db '#] Login please....(ESC to skip login)', 0


    ;/////////////////////////////////////////////////////////////
    ; defining printing string functions here

    ;****** print string without color

print_string:
    mov ah, 0x0E            ; value to tell interrupt handler that take value from al & print it

.repeat_next_char:
    lodsb                ; get character from string
    cmp al, 0                    ; cmp al with end of string
    je .done_print               ; if char is zero, end of string
    int 0x10                     ; otherwise, print it
    jmp .repeat_next_char        ; jmp to .repeat_next_char if not 0

.done_print:
    ret                         ;return

;****** print string with different colors

_print_DiffColor_String:
        mov bl,1                ;color value
    mov ah, 0x0E

.repeat_next_char:
    lodsb
    cmp al, 0
    je .done_print
    add bl,6               ;increase color value by 6
    int 0x10
    jmp .repeat_next_char

.done_print:
    ret

;****** print string with green color

_print_GreenColor_String:
    mov bl,10
    mov ah, 0x0E

.repeat_next_char:
    lodsb
    cmp al, 0
    je .done_print
    int 0x10
    jmp .repeat_next_char

.done_print:
    ret

;****** print string with white color

_print_WhiteColor_String:
    mov bl,15
    mov ah, 0x0E

.repeat_next_char:
    lodsb
    cmp al, 0
    je .done_print
    int 0x10
    jmp .repeat_next_char

.done_print:
    ret

;****** print string with yellow color

_print_YellowColor_String:
    mov bl,14
    mov ah, 0x0E

.repeat_next_char:
    lodsb
    cmp al, 0
    je .done_print
    int 0x10
    jmp .repeat_next_char

.done_print:
    ret


    ;///////////////////////////////////////////
    ; boot loader magic number
    times ((0x200 - 2) - ($ - $$)) db 0x00     ;set 512 bytes for boot sector which are necessary
    dw 0xAA55                                  ; boot signature 0xAA & 0x55


;////////////////////////////////////////////////////////////////////////////////////////

_OS_Stage_2 :

    mov al,2                    ; set font to normal mode
    mov ah,0                    ; clear the screen
    int 0x10                    ; call video interrupt

    mov cx,0                    ; initialize counter(cx) to get input

    ;***** print login_label on screen
    ;set cursor to specific position on screen
    mov ah,0x02
    mov bh,0x00
    mov dh,0x00
    mov dl,0x00
    int 0x10

    mov si,login_label              ; point si to login_username
    call print_string               ; display it on screen

    ;****** read username

    ;set cursor to specific position on screen
    mov ah,0x02
    mov bh,0x00
    mov dh,0x02
    mov dl,0x00
    int 0x10

    mov si,login_username          ; point si to login_username
    call print_string              ; display it on screen

_getUsernameinput:

    mov ax,0x00             ; get keyboard input
    int 0x16                ; hold for input

    cmp ah,0x1C             ; compare input is enter(1C) or not
    je .exitinput           ; if enter then jump to exitinput

    cmp ah,0x01             ; compare input is escape(01) or not
    je _skipLogin           ; jump to _skipLogin

    mov ah,0x0E             ;display input char
    int 0x10

    inc cx                  ; increase counter
    cmp cx,5                ; compare counter reached to 5
    jbe _getUsernameinput   ; yes jump to _getUsernameinput
    jmp .inputdone          ; else jump to inputdone

.inputdone:
    mov cx,0                ; set counter to 0
    jmp _getUsernameinput   ; jump to _getUsernameinput
    ret                     ; return

.exitinput:
    hlt


    ;****** read password

    ;set x y position to text
    mov ah,0x02
    mov bh,0x00
    mov dh,0x03
    mov dl,0x00
    int 0x10

    mov si,login_password               ; point si to login_username
    call print_string                   ; display it on screen

_getPasswordinput:

    mov ax,0x00
    int 0x16

    cmp ah,0x1C
    je .exitinput

    cmp ah,0x01
    je _skipLogin

    inc cx

    cmp cx,5
    jbe _getPasswordinput

    jmp .inputdone

.inputdone:
    mov cx,0
    jmp _getPasswordinput
    ret
.exitinput:
    hlt

;****** display display_text on screen

    ;set x y position to text
    mov ah,0x02
    mov bh,0x00
    mov dh,0x08
    mov dl,0x12
    int 0x10

    mov si, display_text        ;display display_text on screen
    call print_string

    ;set x y position to text
    mov ah,0x02
    mov bh,0x00
    mov dh,0x9
    mov dl,0x10
    int 0x10

    mov si, os_info     ;display os_info on screen
    call print_string

    ;set x y position to text
    mov ah,0x02
    mov bh,0x00
    mov dh,0x11
    mov dl,0x11
    int 0x10

    mov si, press_key_2     ;display press_key_2 on screen
    call print_string

    mov ah,0x00
    int 0x16


;//////////////////////////////////////////////////////////////////

_skipLogin:

    ;/////////////////////////////////////////////////////////////
    ; load third sector into memory

    mov ah, 0x03                    ; load third stage to memory
    mov al, 1
    mov dl, 0x80
    mov ch, 0
    mov dh, 0
    mov cl, 3                       ; sector number 3
    mov bx, _OS_Stage_3
    int 0x13

    jmp _OS_Stage_3

;////////////////////////////////////////////////////////////////////////////////////////

_OS_Stage_3:

    mov ax,0x13              ; clears the screen
    int 0x10

;//////////////////////////////////////////////////////////
; drawing window with lines

    push 0x0A000                ; video memory graphics segment
    pop es                      ; pop any extar segments from stack
    xor di,di                   ; set destination index to 0
    xor ax,ax                   ; set color register to zero

    ;//////////////////////////////////////////////
    ;******drawing top line of our window
    mov ax,0x02                 ; set color to green

    mov dx,0                    ; initialize counter(dx) to 0

    add di,320                  ; add di to 320(next line)
    imul di,10                  ;multiply by 10 to di to set y cordinate from where we need to start drawing

    add di,10                   ;set x cordinate of line from where to be drawn

_topLine_perPixel_Loop:

    mov [es:di],ax              ; move value ax to memory location es:di

    inc di                      ; increment di for next pixel
    inc dx                      ; increment our counter
    cmp dx,300                  ; comprae counter value with 300
    jbe _topLine_perPixel_Loop  ; if <= 300 jump to _topLine_perPixel_Loop

    hlt                         ; halt process after drawing

    ;//////////////////////////////////////////////
    ;******drawing bottm line of our window
    xor dx,dx
    xor di,di
    add di,320
    imul di,190         ; set y cordinate for line to be drawn
    add di,10           ;set x cordinate of line to be drawn

    mov ax,0x01         ; blue color

_bottmLine_perPixel_Loop:

    mov [es:di],ax

    inc di
    inc dx
    cmp dx,300
    jbe _bottmLine_perPixel_Loop
    hlt

    ;//////////////////////////////////////////////
    ;******drawing left line of our window
    xor dx,dx
    xor di,di
    add di,320
    imul di,10           ; set y cordinate for line to be drawn

    add di,10            ; set x cordinate for line to be drawn

    mov ax,0x03          ; cyan color

_leftLine_perPixel_Loop:

    mov [es:di],ax

    inc dx
    add di,320
    cmp dx,180
    jbe _leftLine_perPixel_Loop

    hlt

    ;//////////////////////////////////////////////
    ;******drawing right line of our window
    xor dx,dx
    xor di,di
    add di,320
    imul di,10           ; set y cordinate for line to be drawn

    add di,310           ; set x cordinate for line to be drawn

    mov ax,0x06          ; orange color

_rightLine_perPixel_Loop:

    mov [es:di],ax

    inc dx
    add di,320
    cmp dx,180
    jbe _rightLine_perPixel_Loop

    hlt

    ;//////////////////////////////////////////////
    ;******drawing line below top line of our window
    xor dx,dx
    xor di,di

    add di,320
    imul di,27           ; set y cordinate for line to be drawn

    add di,11            ; set x cordinate for line to be drawn

    mov ax,0x05         ; pink color

_belowLineTopLine_perPixel_Loop:

    mov [es:di],ax

    inc di
    inc dx
    cmp dx,298
    jbe _belowLineTopLine_perPixel_Loop

    hlt

    ;***** print window_text & X char

    ;set cursor to specific position
    mov ah,0x02
    mov bh,0x00
    mov dh,0x01         ; y cordinate
    mov dl,0x02         ; x cordinate
    int 0x10

    mov si,window_text              ; point si to window_text
    call _print_YellowColor_String

    hlt

    ;set cursor to specific position
    mov ah,0x02
    mov bh,0x00
    mov dh,0x02           ; y cordinate
    mov dl,0x25           ; x cordinate
    int 0x10

    mov ah,0x0E
    mov al,0x58           ; 0x58=X
    mov bh,0x00
    mov bl,4              ; red color
    int 0x10

    hlt

    ;set cursor to specific position
    mov ah,0x02
    mov bh,0x00
    mov dh,0x02           ; y cordinate
    mov dl,0x23           ; x cordinate
    int 0x10

    mov ah,0x0E
    mov al,0x5F           ; 0x58=X
    mov bh,0x00
    mov bl,9              ; red color
    int 0x10

    hlt

    ;set cursor to specific position
    mov ah,0x02
    mov bh,0x00
    mov dh,0x05   ; y cordinate
    mov dl,0x09    ; x cordinate
    int 0x10

    mov si,hello_world_text
    call _print_DiffColor_String

    hlt

    ;set cursor to specific position
    mov ah,0x02
    mov bh,0x00
    mov dh,0x12   ; y cordinate
    mov dl,0x03  ; x cordinate
    int 0x10

    mov si,display_text
    call _print_WhiteColor_String

    hlt


    ; add how much memory we need
    times (1024 - ($-$$)) db 0x00