126 lines
1.7 KiB
NASM
126 lines
1.7 KiB
NASM
section .bss
|
|
|
|
clus resw 1
|
|
|
|
section .text
|
|
|
|
; Set cluster for next operations
|
|
; IN dx cluster number
|
|
setclus mov [clus], dx
|
|
ret
|
|
|
|
; get ptr to single byte in fat table
|
|
; IN dx position byte in fat table
|
|
; OUT bx ptr to byte in dskbuf
|
|
_fat1 push dx
|
|
mov ax, dx
|
|
xor dx, dx
|
|
mov cl, 9
|
|
shr ax, cl
|
|
add ax, [bpb+BPBRSC]
|
|
adc dx, 0
|
|
call map
|
|
pop dx
|
|
mov bx, dx
|
|
and bx, 0x1FF
|
|
add bx, dskbuf
|
|
ret
|
|
|
|
; get ptr to word in fat table
|
|
_fat2 push dx
|
|
mov ax, dx
|
|
xor dx, dx
|
|
mov cl, 8
|
|
shr ax, cl
|
|
add ax, [bpb+BPBRSC]
|
|
adc dx, 0
|
|
call map
|
|
pop dx
|
|
mov bl, dl
|
|
mov bh, 0
|
|
add bx, bx
|
|
add bx, dskbuf
|
|
ret
|
|
|
|
; read value from fat table
|
|
; index given with setclus
|
|
; OUT bx value
|
|
; carry set if EOF marker
|
|
rdfat mov dx, [clus]
|
|
mov ax, dx
|
|
shr ax, 1
|
|
add dx, ax
|
|
call _fat1
|
|
push word [bx]
|
|
inc dx
|
|
call _fat1
|
|
mov si, bx
|
|
pop bx
|
|
mov bh, [si]
|
|
test word [clus], 1
|
|
jz l001
|
|
mov cl, 4
|
|
shr bx, cl
|
|
l001 and bx, 0xFFF
|
|
cmp bx, 0xFF0
|
|
cmc
|
|
ret
|
|
|
|
; set value in FAT table
|
|
; IN dx value
|
|
wrfat and dh, 0x0F
|
|
push dx
|
|
; DX = index * 1.5
|
|
mov dx, [clus]
|
|
mov ax, dx
|
|
shr dx, 1
|
|
add dx, ax
|
|
call _fat1
|
|
pop ax
|
|
test [clus], 1
|
|
jnz l004
|
|
; even, first byte full
|
|
mov [bx], al
|
|
push ax
|
|
call dirty
|
|
; DX = index * 1.5
|
|
mov dx, [clus]
|
|
mov ax, dx
|
|
shr dx, 1
|
|
add dx, ax
|
|
inc dx
|
|
call _fat1
|
|
pop ax
|
|
mov al, [bx]
|
|
and al, 0xF0
|
|
or al, ah
|
|
mov [bx], al
|
|
call dirty
|
|
jmp l005
|
|
; odd, second byte full
|
|
l004: mov ch, [bx]
|
|
; concat existing and our nib
|
|
and ch, 0x0F
|
|
mov cl, 4
|
|
shl ax, cl
|
|
or al, ch
|
|
; write back lower 4 bits
|
|
mov [bx], al
|
|
call dirty
|
|
push ax
|
|
; re-calculate offset
|
|
mov ax, dx
|
|
shr dx, 1
|
|
add dx, ax
|
|
inc dx
|
|
; map second byte
|
|
call _fat1
|
|
pop ax
|
|
; write higher 8 bits
|
|
mov [bx], ah
|
|
call dirty
|
|
l005: ret
|
|
|
|
; wrfat from above, FAT16 flavour
|
|
wf16: ret
|