rdos/kernel/fcb.asm

90 lines
1.9 KiB
NASM
Raw Normal View History

2019-10-14 19:59:48 +02:00
; diskbuf needs to be defined
2019-10-08 19:54:39 +02:00
; User-accessible part of FCB (12 bytes)
fcb_drv: equ 0 ; 1 byte, 1=A: 2=B: 3=C:
fcb_fn: equ 1 ; 8 bytes
fcb_ext: equ 9 ; 3 bytes
2019-10-08 19:54:39 +02:00
2019-10-12 20:33:26 +02:00
; Drive & FS data (6 bytes)
fcb_spt: equ 12 ; byte sectors per track
fcb_nos: equ 13 ; byte number of sides/heads
fcb_ss: equ 14 ; byte sector size: 0=128, 1=256, 2=512, ...
fcb_cs: equ 15 ; byte cluster size: 0=128, 1=256, 2=512, ...
fcb_co: equ 16 ; word start sector for theoretical cluster 0
2019-10-12 20:33:26 +02:00
; Read/Write pointer (6 bytes)
fcb_left: equ 18 ; word number of bytes left to read from diskbuf
fcb_off: equ 20 ; dword offset in disk (not in file)
2019-10-12 20:33:26 +02:00
; Link to directory item (4 bytes)
fcb_ds: equ 24 ; dword offset of directory item
2019-10-12 20:33:26 +02:00
fcb_end: equ 32
2019-10-12 20:33:26 +02:00
2019-10-14 19:59:48 +02:00
fcb_open_rootdir:
2019-10-12 20:33:26 +02:00
mov dl, 0x01
mov [bx], dl
2019-09-29 23:25:29 +02:00
dec dl
2019-10-14 19:59:48 +02:00
; Setup default data
; Default 2 heads, 9 sectors
mov word [bx+fcb_spt], 0x0209
2019-10-08 19:54:39 +02:00
xor ax, ax
2019-10-14 19:59:48 +02:00
lea di, [bx+fcb_ss]
; Sector & Cluster size 128 bytes
mov cx, (fcb_end - fcb_ss)
2019-10-12 20:33:26 +02:00
rep stosb
2019-10-08 19:54:39 +02:00
; load first sector
call drive_read
2019-10-12 20:33:26 +02:00
; copy sector size
2019-10-08 19:54:39 +02:00
mov ax, [diskbuf + 0x0B]
; ... save as number of valid bytes in diskbuf
mov WORD [bx+fcb_left], ax
2019-10-08 19:54:39 +02:00
call log2
2019-10-12 20:33:26 +02:00
sub ax, 7
; ... save as sector size
2019-10-08 19:54:39 +02:00
mov byte [bx+fcb_ss], al
2019-10-12 20:33:26 +02:00
; copy cluster size
xor ah, ah
2019-10-08 19:54:39 +02:00
mov al, [diskbuf + 0x0D]
call log2
2019-10-12 20:33:26 +02:00
add al, [bx+fcb_ss]
2019-10-08 19:54:39 +02:00
mov byte [bx+fcb_cs], al
; copy sectors per track
2019-10-08 19:54:39 +02:00
mov al, [diskbuf + 0x18]
mov byte [bx+fcb_spt], al
; copy number of heads/sides
2019-10-08 19:54:39 +02:00
mov al, [diskbuf + 0x1A]
mov byte [bx+fcb_nos], al
2019-09-29 23:25:29 +02:00
2019-10-12 20:33:26 +02:00
ret
fcb_get_sector_mask:
push cx
xor ax, ax
not ax
mov cl, [bx+fcb_ss]
add cl, 7
shl ax, cl
pop cx
ret
fcb_getc:
push bx
call fcb_get_sector_mask
not ax
and ax, [bx+fcb_off]
xchg ax, bx
add bx, diskbuf
mov al, [bx]
pop bx
add word [bx+fcb_off], 1
adc word [bx+fcb_off+2], 0
dec word [bx+fcb_left]
2019-09-29 14:23:39 +02:00
ret