SO78264246

org 0x7C00
bits 16

mov ax, 0
mov es, ax
mov ds, ax
mov ss, ax
mov sp, 0x7c00 ; Stack will grow down below the bootloader.
mov [bdv], dl

jmp main


; lbaRead
; Reads sectors using LBA
; bx: LBA Address
; ax: Number of sectors
; dl: Drive number
lbaRead:
    ; Save AX and BX
    mov [snm], ax
    push bx

    ; Read the Disk Geometry
    mov ah, 8
    mov di, 0
    int 0x13
    ; Error Handling
    jc err
    ; continue
    ; Int 0x13/ah=8 can set ES to non zero segment
    ; set ES back to 0
    mov ax, 0
    mov es, ax

    inc dh
    mov [hct], dh
    and cl, 0x3F
    mov [spt], cl

    ; Restore BX clobbered by previous int 13h
    pop bx

    ; Convert LBA to CHS
    ; Calculate temporary value (tmp) and sector
    mov dx, 0
    mov ax, bx
    mov bx, [spt]
    div bx
    inc dl
    mov [sct], dl
    ; Calculate Head and Cylinder
    mov dx, 0
    mov bx, [hct]
    div bx
    mov [hed], dl
    mov [cyl], ax

    ; Read the disk
    mov ah, 0x02
    mov al, [snm]
    mov ch, [cyl]
    mov cl, [sct]
    mov dh, [hed]
    mov dl, [bdv]
    mov bx, 0x7E00
    int 0x13
    ; Error handling
    jc err
    ret

main:
    pusha
    mov bx, 1
    mov ax, 1
    call lbaRead
    popa

    mov ah, 0x0E
    mov al, [0x7E00]
    int 0x10
    jmp $

err:
    mov ah, 0x0B
    mov bl, 0x4
    int 0x10
    jmp $

; Variables for CHS conversion
tmp: dw 0
sct: db 0
hed: db 0
cyl: dw 0
spt: dw 0
hct: dw 0
bdv: db 0
snm: dw 0

; Pad to 512 bytes and add 0x55AA cap
times 510-($-$$) db 0
db 0x55, 0xaa