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