90 lines
1.9 KiB
NASM
90 lines
1.9 KiB
NASM
; diskbuf needs to be defined
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; User-accessible part of FCB (12 bytes)
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fcb_drv: equ 0 ; 1 byte, 1=A: 2=B: 3=C:
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fcb_fn: equ 1 ; 8 bytes
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fcb_ext: equ 9 ; 3 bytes
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; Drive & FS data (6 bytes)
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fcb_spt: equ 12 ; byte sectors per track
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fcb_nos: equ 13 ; byte number of sides/heads
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fcb_ss: equ 14 ; byte sector size: 0=128, 1=256, 2=512, ...
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fcb_cs: equ 15 ; byte cluster size: 0=128, 1=256, 2=512, ...
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fcb_co: equ 16 ; word start sector for theoretical cluster 0
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; Read/Write pointer (6 bytes)
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fcb_left: equ 18 ; word number of bytes left to read from diskbuf
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fcb_off: equ 20 ; dword offset in disk (not in file)
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; Link to directory item (4 bytes)
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fcb_ds: equ 24 ; dword offset of directory item
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fcb_end: equ 32
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fcb_open_rootdir:
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mov dl, 0x01
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mov [bx], dl
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dec dl
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; Setup default data
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; Default 2 heads, 9 sectors
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mov word [bx+fcb_spt], 0x0209
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xor ax, ax
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lea di, [bx+fcb_ss]
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; Sector & Cluster size 128 bytes
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mov cx, (fcb_end - fcb_ss)
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rep stosb
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; load first sector
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call drive_read
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; copy sector size
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mov ax, [diskbuf + 0x0B]
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; ... save as number of valid bytes in diskbuf
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mov WORD [bx+fcb_left], ax
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call log2
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sub ax, 7
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; ... save as sector size
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mov byte [bx+fcb_ss], al
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; copy cluster size
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xor ah, ah
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mov al, [diskbuf + 0x0D]
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call log2
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add al, [bx+fcb_ss]
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mov byte [bx+fcb_cs], al
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; copy sectors per track
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mov al, [diskbuf + 0x18]
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mov byte [bx+fcb_spt], al
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; copy number of heads/sides
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mov al, [diskbuf + 0x1A]
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mov byte [bx+fcb_nos], al
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ret
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fcb_get_sector_mask:
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push cx
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xor ax, ax
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not ax
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mov cl, [bx+fcb_ss]
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add cl, 7
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shl ax, cl
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pop cx
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ret
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fcb_getc:
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push bx
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call fcb_get_sector_mask
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not ax
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and ax, [bx+fcb_off]
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xchg ax, bx
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add bx, diskbuf
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mov al, [bx]
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pop bx
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add word [bx+fcb_off], 1
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adc word [bx+fcb_off+2], 0
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dec word [bx+fcb_left]
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ret
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