Preparing for rewriting load_sectors
This commit is contained in:
Eric-Paul Ickhorn
parent
6d9ad157fb
commit
4887c61303
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@ -1,6 +1,203 @@
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section .text
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initialize_video_mode:
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.prolog:
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push ax
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; set the video mode correctly
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xor ah, ah ; bios-function (set video mode)
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mov al, 3 ; video mode with 80x25 characters
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int 0x10
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.epilog:
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pop ax
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ret
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; cx: len_buffer
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; si: buffer
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; dl: start_x NOTE: Will contain the end of the text on-screen
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; dh: start_y NOTE: Will contain the end of the text on-screen
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print_string:
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.prolog:
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push di
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push cx
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push bx
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push ax
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xor di, di ; character index
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.printing_loop:
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.set_cursor_position:
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mov ah, 0x02
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mov bh, 0
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int 0x10
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.write_character:
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push cx ; save len_buffer
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; get the current character
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mov bx, si
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add bx, di
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mov al, [bx]
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; al now contains the current character
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; set the other needed interrupt values
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mov ah, 0x0a ; wanted function (write character at cursor position)
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mov bh, 0 ; page number
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mov cx, 1 ; repetitions of character
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int 0x10 ; call bios basic draw functions
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pop cx ; restore len_buffer
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inc dl ; go to next column
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; go to a new line if needed
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cmp dl, 80
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jb .no_new_line_needed
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xor dl, dl
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inc dh ; increase column
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.no_new_line_needed:
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inc di ; go to next character
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; go further if the string-printing hasn't been finished
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cmp di, cx
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jb .printing_loop
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.epilog:
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pop ax
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pop bx
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pop cx
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pop di
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ret
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; ds: source
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; es: destination
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; dx: len_to_copy
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mem_copy:
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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 cx, cx
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mov di, dx
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; ax: first region's value
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; bx: address at index
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; cx: byte_index
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; dx: second region's value
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.loop:
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; retrieve the source byte at the current index
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mov bx, cx
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mov dx, [bx]
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; swap the two segments
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; here, ax and bx are used differently.
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mov ax, es
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mov bx, ds
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mov ds, ax
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mov es, bx
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mov [bx], cx
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; swap the two segments back
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mov ax, es
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mov bx, ds
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mov ds, ax
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mov es, bx
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inc cx
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; if the end has NOT been reached
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cmp cx, di
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jb .loop ; => continue
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ret
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; ds: region_1
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; es: region_2
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; dx: len_regions
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; ax: result
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mem_equals:
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push bx
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push cx
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push dx
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push di
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xor cx, cx
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mov di, dx
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; ax: first region's value
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; bx: address at index
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; cx: byte_index
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; dx: second region's value
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.loop:
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mov bx, cx
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mov dx, [bx]
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; swap the two segments
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; here, ax and bx are used differently.
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mov ax, es
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mov bx, ds
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mov ds, ax
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mov es, bx
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mov bx, cx
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mov ax, [bx]
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cmp ax, dx
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; swap the two segments back
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mov ax, es
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mov bx, ds
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mov ds, ax
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mov es, bx
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; jump accordingly to the comparison above
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jne .not_equal
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inc cx
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cmp cx, di ; if the loop needs to continue
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jb .loop ; (if the end is NOT reached yet)
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; it goes here if the two regions are completely equal
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pop di
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pop dx
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pop cx
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pop bx
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mov ax, 1
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ret
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.not_equal:
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pop di
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pop dx
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pop cx
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pop bx
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mov ax, 0
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ret
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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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@ -14,28 +211,40 @@ load_sectors:
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push bx
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push cx
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push dx
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push si
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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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; calculate the distance (in sectors) to the next cylinder boundary
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; get the index of the current cylinder
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and ax, 0b00111111 ; extract only the sector index
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mov bx, 64 ; get the maximum number of sectors + 1
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sub bx, ax ; invert the result; 1 becomes 63; 63 becomes 1
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cmp ax, 63
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jne .is_not_on_full_cylinder_boundary
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; if it's indeed on a full cylinder boundary, the first_read-part is unimportant
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mov ax, 0
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set_load_args
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.is_not_on_full_cylinder_boundary:
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; cx still contains the entry-point's wanted sector_count
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; ax now contains the distance to the next cylinder boundary
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cmp cx, ax
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jbe .load_data
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; it gets here if there are more sectors needed after the
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; next cylinder boundary
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; if the number of sectors
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; which are wanted (sector_count) is above the
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; distance to the 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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@ -53,22 +262,26 @@ load_sectors:
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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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cmp cx, 63
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jbe .add_num_missing_sectors_to_sector_index
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; if this goes here, there are more than 63 sectors
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; still missing to be loaded
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; -> clamp them to 63 so they can be loaded.
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mov cl, 63
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jmp .load_data
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.add_num_missing_sectors_to_sector_index:
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add si, cx
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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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; bx: start_sector (high part)
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; ch: start_sector (low 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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@ -86,12 +299,13 @@ load_sectors:
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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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jb .set_load_args
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.epilog:
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pop si
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pop dx
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pop cx
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pop bx
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