section .text

; ax: start_sector (lower)
; bl: start_sector (upper)
; cx: sector_count
; dh: drive
; es: buffer_address (upper)
; di: buffer_address (lower)
load_sectors:
    
.prolog:
    push ax
    push bx
    push cx
    push dx
    
    xor si, si          ; current sector index
    
; sets the arguments for the first run of '.load_data'
; which loads until the first CHS - cylinder boundary
.set_first_load_args:
    
    ; the first read only reads up to the next cylinder boundary,
    ; but potentially less (if not that many sectors have been requested)
    
    ; TODO================================================================================
    mov bx, sp
    add bx, 4
    mov cx, [bx]        ; get sector count
    sub cx, si          ; cx = num_missing_sectors
    
    
    mov bx, sp
    mov bx, [bx]
    cmp cx, bx
    js .load_data       ; if there are more sectors needed after the
                        ; next cylinder boundary
    ; if not that many sectors are needed, just read as
    ; many sectors as are needed in total
    mov cx, bx
    
    jmp .load_data
    
    
    
; sets the arguments for a run of '.load_data' after the
; first one; aligned on a CHS - cylinder boundary
.set_load_args:
    
    mov bx, sp
    add bx, 4
    mov cx, [bx]
    sub cx, si          ; cx = num_missing_sectors
    
    cmp cx, 64
    js .load_data
    ; if this goes here, there are more than 64 sectors missing
    ; -> clamp them to 64 so they can be loaded.
    mov cl, 64
    jmp .load_data      ; redundant
    
; loads at most 64 sectors from the disk into the main memory
; ax: scratchpad
; bx: start_sector (low part)
; ch: start_sector (high part)
; cl: num_sectors
.load_data:
    
    mov bx, sp
    
    mov ah, 0x02
    mov al, cl
    mov dl, [bx]        ; drive
    mov dh, bh          ; head
    mov cl, ch          ; sector
    mov ch, bl          ; cylinder
    mov bx, di          ; buffer address (lower)
    int 0x13
    
.continue_if_needed:
    
    ; check if there still are sectors missing to load
    mov bx, sp
    add bx, 4
    mov cx, [bx]        ; sector_count
    
    cmp si, cx
    js .set_load_args
    
    
    
.epilog:
    
    pop dx
    pop cx
    pop bx
    pop ax
    
    ret