170 lines
2.4 KiB
Plaintext
170 lines
2.4 KiB
Plaintext
w_roodir_remaining dw ROOTDIR_TOT_SECTORS
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w_cur_sector_num dw 0
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;
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; fat12_read_file(u16 segment, u16 offset, uintptr (ds:)filename)
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;
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fat12_read_file:
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push bp
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mov bp,sp
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push bp
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; reset the drive
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xor ah, ah
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xor dl, dl
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int 13h
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mov word [w_cur_sector_num], ROOTDIR_SEC_NUM
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.loop_rootdir:
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cmp word [w_roodir_remaining], 0
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jz .not_found
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dec word [w_roodir_remaining]
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mov ax, [ss:bp+4]
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mov es, ax
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mov bx, [ss:bp+6]
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mov ax, [w_cur_sector_num]
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mov cl, 1
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call read_sector
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mov si, [ss:bp+8]
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mov di, [ss:bp+6]
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cld
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mov dx, 10h
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.loop_find_file:
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cmp dx, 0
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jnz .loop_find_file_ctn
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; We traversed all entires in the root dir
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add word [w_cur_sector_num], 1
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jmp .loop_rootdir
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.loop_find_file_ctn:
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dec dx
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mov cx, 11
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.loop_strcmp:
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cmp cx, 0
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jz .found
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dec cx
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lodsb
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cmp al, byte [es:di]
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jnz .loop_strcmp_diff
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inc di
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jmp .loop_strcmp
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.loop_strcmp_diff:
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and di, 0FFE0h
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add di, 20h
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mov si, [ss:bp+8]
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jmp .loop_find_file;
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.found:
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mov ax, ROOTDIR_TOT_SECTORS
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and di, 0FFE0h
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add di, 01Ah
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mov cx, word [es:di]
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push cx
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add cx, ax
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add cx, SECTOR_DELTA
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mov ax, [ss:bp+4]
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mov es, ax
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mov bx, [ss:bp+6]
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mov ax, cx
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.loop_readfile:
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mov cl, 1
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call read_sector
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pop ax
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push word [ss:bp+4]
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call read_fat_entry
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add sp,2
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cmp ax, 0FFFh
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jz .end
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push ax
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mov dx, ROOTDIR_TOT_SECTORS
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add ax, dx
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add ax, SECTOR_DELTA
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add bx, [BPB_BytsPerSec]
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jmp .loop_readfile
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.not_found:
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mov ax, 1
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.end:
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mov sp,[bp-2]
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pop bp
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ret
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read_sector:
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push bp
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mov bp, sp
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sub esp, 2
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mov byte [bp-2], cl
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push bx
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mov bl, [BPB_SecPerTrk]
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div bl
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inc ah
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mov cl, ah
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mov dh, al
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shr al, 1
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mov ch, al
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and dh, 1
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pop bx
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mov dl, [BS_DrvNum]
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.retry:
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mov ah, 2
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mov al, byte [bp-2]
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int 13h
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jc .retry
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add sp, 2
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pop bp
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ret
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b_is_odd_cluster db 0
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read_fat_entry:
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push bp
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mov bp, sp
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push es
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push bx
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push ax
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mov ax, [ss:bp+4]
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sub ax, 0100h
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mov es, ax
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pop ax
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mov byte [b_is_odd_cluster], 0
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mov bx, 3
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mul bx
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mov bx, 2
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div bx
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cmp dx, 0
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jz .even
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mov byte [b_is_odd_cluster], 1
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.even:
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xor dx, dx
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mov bx, [BPB_BytsPerSec]
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div bx
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push dx
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mov bx, 0
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add ax, FAT1_SECTOR_NUM
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mov cl, 2
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call read_sector
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pop dx
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add bx, dx
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mov ax, [es:bx]
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cmp byte [b_is_odd_cluster], 1
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jnz .end
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shr ax, 4
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.end:
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and ax, 0FFFh
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pop bx
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pop es
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pop bp
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ret
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