; first_stage.asm
[org 0x7C00]
SECOND_STAGE_ADDRESS equ 0x7E00 ; Just after the first stage

; Basic setup
cli
xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax
mov sp, 0x7C00

; Print debug message: "F" for First stage
mov ah, 0x0E
mov al, 'F'
int 0x10

; Print newline
mov al, 0x0D
int 0x10
mov al, 0x0A
int 0x10

; Save boot drive number
mov [0x7C1E], dl

; Print debug message: "L" for Loading second stage
mov ah, 0x0E
mov al, 'L'
int 0x10

; Load the second stage
mov ah, 0x02                    ; BIOS read function
mov al, 2                       ; Number of sectors to read
mov ch, 0                       ; Cylinder 0
mov cl, 2                       ; Sector 2 (1-indexed)
mov dh, 0                       ; Head 0
mov dl, [0x7C1E]                ; Drive number
mov bx, SECOND_STAGE_ADDRESS    ; Where to load the second stage

int 0x13                        ; BIOS interrupt to read sectors
jc error                        ; If carry flag was set, there was an error

; Print debug message: "S" for Switching to second stage
mov ah, 0x0E
mov al, 'S'
int 0x10

; Jump to second stage
jmp SECOND_STAGE_ADDRESS

error:
; Print E for error
mov ah, 0x0E
mov al, 'E'
int 0x10
jmp $

BOOT_DRIVE db 0

times 510-($-$$) db 0
dw 0xAA55