[BITS 16]
[ORG 0x7C00]

    ; Initialize segment registers
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov sp, 0x7C00

    ; Reset disk system
    mov ah, 0
    int 0x13
    
    ; Load FAT32 BPB
    mov si, bpb_oem_name
    mov di, 0x7E00
    mov cx, bpb_size
    rep movsb

    ; Read FAT32 root directory
    mov ax, [bpb_reserved_sectors]
    mov [dapack.lba_start], ax
    
    mov ah, 0x42
    mov si, dapack
    int 0x13
    jc error

    ; Find kernel file
    mov si, kernel_name
    mov di, 0x8000
    mov cx, 11      ; FAT32 8.3 filename length
    
find_kernel:
    push cx
    push si
    push di
    rep cmpsb
    pop di
    pop si
    pop cx
    je found_kernel
    
    add di, 32      ; Move to next directory entry
    cmp di, 0x8200  ; Check if we've reached the end of the sector
    jl find_kernel
    
    ; Kernel not found
    mov si, err_no_kernel
    call print
    jmp $

found_kernel:
    ; Get cluster number
    mov ax, [di + 20]  ; High word
    shl eax, 16
    mov ax, [di + 26]  ; Low word
    
    ; Load kernel
    mov [cluster], eax
    call load_cluster
    
    ; Jump to kernel
    jmp 0x8000

error:
    mov si, err_disk
    call print
    jmp $

print:
    lodsb
    or al, al
    jz .done
    mov ah, 0x0E
    int 0x10
    jmp print
.done:
    ret

load_cluster:
    ; Convert cluster to LBA
    sub eax, 2
    mul dword [sectors_per_cluster]
    add eax, [first_data_sector]
    
    mov [dapack.lba_start], eax
    mov ah, 0x42
    mov si, dapack
    int 0x13
    ret

align 4
dapack:
    db 0x10   ; Size of packet
    db 0      ; Reserved
    dw 1      ; Number of sectors
    dw 0x8000 ; Offset
    dw 0      ; Segment
    dq 0      ; LBA

cluster:      dd 0
sectors_per_cluster: dd 8
first_data_sector:  dd 0

kernel_name:  db "KERNEL  BIN"
err_disk:     db "Disk error", 0
err_no_kernel: db "No kernel", 0

bpb_oem_name:         times 8 db 0
bpb_bytes_per_sector: dw 512
bpb_sectors_per_cluster: db 8
bpb_reserved_sectors: dw 32
bpb_size: equ $ - bpb_oem_name

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