rulimine/stage1/hdd/disk.asm

; *****************************
;     Reads bytes from disk
; *****************************

; IN:
; EAX = Start address to load low 32
; EBP = Start address to load high 32
; DL = Drive number
; ES = Buffer segment
; BX = Buffer offset
; ECX = Byte count

; OUT:
; Carry if error

read_sectors:
    pusha

    mov si, .da_struct

    mov word  [si],    16
    mov word  [si+2],  1
    mov word  [si+4],  bx
    mov word  [si+6],  es

    push dx
    push si

    push eax
    push ebp

    ; Get bytes per sector
    mov ah, 0x48
    mov si, .drive_params
    mov word [si], 30       ; buf_size
    int 0x13
    jc .done
    mov bp, word [si+24]    ; bytes_per_sect

    ; ECX byte count to CX sector count
    mov ax, cx
    shr ecx, 16
    mov dx, cx
    xor cx, cx
    div bp
    test dx, dx
    setnz cl
    add cx, ax

    pop edx
    pop eax

    pop si

    ; EBP:EAX address to EAX LBA sector
    div ebp
    mov dword [si+8],  eax
    mov dword [si+12], 0

    pop dx

  .loop:
    mov ah, 0x42

    clc
    int 0x13
    jc .done

    add word  [si+4], bp
    inc dword [si+8]
    adc dword [si+12], 0

    loop .loop

  .done:
    popa
    ret

  .da_struct:    equ 0x8000
  .drive_params: equ 0x8010