; File: boot.asm
; Stage 1 Bootloader (Master Boot Record - exactly 512 bytes)
; Job: Load Stage 2 from disk and jump to it

[org 0x7c00]
[bits 16]

STAGE2_OFFSET equ 0x7e00    ; Load stage2 right after boot sector

start:
    ; Set up segments
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov sp, 0x7c00
    
    ; IMPORTANT: Save boot drive number (BIOS passes it in DL)
    push dx

    ; Clear screen
    mov ah, 0x00
    mov al, 0x03
    int 0x10

    ; Print loading message
    mov si, msg_loading
    call print_string

    ; Load Stage 2 from disk
    ; Read 5 sectors (sectors 2-6) - gives us 2.5KB for Stage 2
    pop dx                  ; Restore boot drive
    push dx                 ; Save it again for stage 2
    mov bx, STAGE2_OFFSET   ; Destination
    mov dh, 5               ; Number of sectors
    ; DL already has drive number
    call load_disk

    ; Jump to Stage 2 (DL still has boot drive number)
    pop dx                  ; Pass drive number to stage 2 in DL
    jmp STAGE2_OFFSET

; ============================================================
; LOAD DISK - Read sectors using BIOS INT 0x13
; ============================================================
load_disk:
    push dx
    
    mov ah, 0x02        ; Read function
    mov al, dh          ; Number of sectors
    mov ch, 0           ; Cylinder 0
    mov cl, 2           ; Start at sector 2
    mov dh, 0           ; Head 0
    
    int 0x13
    jc disk_error
    
    pop dx
    cmp al, dh
    jne disk_error
    ret

disk_error:
    mov si, msg_error
    call print_string
    jmp $

; ============================================================
; PRINT STRING
; ============================================================
print_string:
    pusha
    mov ah, 0x0e
.loop:
    lodsb
    test al, al
    jz .done
    int 0x10
    jmp .loop
.done:
    popa
    ret

; ============================================================
; DATA
; ============================================================
msg_loading: db '[STAGE1] Loading SoraOS...', 0x0D, 0x0A, 0
msg_error:   db '[ERROR] Disk read failed!', 0x0D, 0x0A, 0

; ============================================================
; BOOT SIGNATURE
; ============================================================
times 510-($-$$) db 0
dw 0xAA55