org 0x7c00                                              ; starting memory address

; CONSTANTS 
    newline equ 0x0a
    carriageReturn equ 0x0d 
    teletype_function equ 0x0e
    printInterrupt equ 0x10 


start:                                                  ; start lable
    cli                                                 ; clearing interrupts
    xor ax,ax                                           ; setting ax operation to 0, using xor save a byte
    mov ds,ax                                           ; setting the data segment to 0
    mov es,ax                                           ; setting the extra segment to 0
    mov ss,ax                                           ; setting the stack segment to 0
    mov sp,0x7c00                                       ; setting the stack pointer to the starting address
    sti                                                 ; restarting the interrupts
    
    mov si,stage1msg                                    ; moving the source index to the first message


; LOOP TO PRINT THE FIRST message
print_loop1:                                            ; loop to print the first message on the screen
    lodsb                                               ; load the byte from the si to al register then move to the next one
    cmp al,0                                            ; comparing if al=0 
    je new_line                                         ; if al=0 then go to the new line label
    mov ah,teletype_function                            ; bios teletype function loaded into the ah register
    int printInterrupt                                  ; interrupt to print to the screen
    jmp print_loop1                                     ; repeat until 0 is encountered

; NEW LINE
new_line:                                               ; to print the newline
    mov al,newline                                      ; ascii value for line feed function: linebereak to print the message in another line
    mov ah,teletype_function                            ; bios teletype function
    int printInterrupt                                  ; printing to the screen
    mov al,carriageReturn                               ; ascii value for the carriage return: ensures that the cursor is set to the beginning of the new line
    mov ah,teletype_function                            ; bios teletype function
    int printInterrupt                                  ; usdsed to print to the screen

; reading stage 2 from the disk
    mov ah,0x02                                         ; bios read sector, telling the bios to rread from the specified source
    mov al,8                                            ; number of sections to read from the dis, each section is of 512 bytes
    mov ch,0                                            ; specifying which ring of the disk should the data be read from
    mov cl,2                                            ; specifying the section to be read from, sections start from 1 not 0 all the way to 63
    mov dh,0                                            ; which plate to read from, which head to read from
    mov dl,0x00                                         ; specifing the type of drive 0x00 is floppy disk , 0x80 is hard disk, 0x01 is floppy disk 2
    mov bx,0x8000                                       ; read and write location, bios sees this and starts reading from this location
    int 0x13                                            ; interrupt that lets the bios read the file from the above parameters
    jc bootloader_loop                                  ; if failed to read the disk go to the inifnite loop instead of crashing


stage2_jump:
    jmp 0x0000:0x8000                                   ; actual jump segment offset memory location


; LOOP TO KEEP THE BOOTLOADER RUNNING 
bootloader_loop:                                        ; bootloader loop 
    jmp $                                               ; jumping back to the current memory address i.e the bootloader_loop

    stage1msg db "STAGE 1 BOOTLOADER LOADED",0          ; the first message to print to the screen
    times 510 - ( $- $$ ) db 0                          ; setting the remaining bits of the first stage to 0
    dw 0xaa55                                           ; final verification boot signature