185 lines
3.0 KiB
NASM
185 lines
3.0 KiB
NASM
fcb1 equ 0x5C
|
|
|
|
org 0x100
|
|
jmp main
|
|
|
|
%include "scan.inc"
|
|
%include "print.inc"
|
|
|
|
drvnum db 0
|
|
track dw 39
|
|
|
|
main mov di, 0x81
|
|
mov al, 0x20
|
|
mov ch, 0
|
|
mov cl, [0x80]
|
|
repe scasb
|
|
repne scasb
|
|
test cx, cx
|
|
jnz rddrv
|
|
call putsh
|
|
db "BIOS drive number not specified", 0x0A, 0x0D, 0
|
|
int 0x20
|
|
rddrv mov si, di
|
|
call lodnum
|
|
mov dx, ax
|
|
test dx, ~0x83
|
|
jnz drverr
|
|
mov byte [drvnum], dl
|
|
test dl, 0x80
|
|
jz floppy
|
|
call drverr
|
|
|
|
drverr call putsh
|
|
db "Failed to access drive", 0x0A, 0x0D, 0
|
|
int 0x20
|
|
|
|
; read bios parameter block
|
|
floppy mov ax, 0x0201
|
|
mov cx, 0x0001
|
|
mov dh, 0
|
|
mov bx, prog
|
|
int 0x13
|
|
jc drverr
|
|
|
|
mov ax, [prog+0x016]
|
|
cmp ax, 12
|
|
jbe .gok
|
|
call putsh
|
|
db "Unsupported FAT size", 0x0A, 0x0D, 0
|
|
int 0x20
|
|
.gok nop
|
|
|
|
; calculate start of cluster area
|
|
mov ax, [prog+0x011] ; number of dir entries
|
|
mov cl, 5
|
|
shl ax, cl
|
|
mov bx, [prog+0x0B] ; bytes per sector
|
|
div bx
|
|
mov cx, ax
|
|
mov ax, [prog+0x016] ; logical sectors per fat
|
|
mov bl, [prog+0x010] ; number of fats
|
|
mov bh, 0
|
|
mul bx
|
|
add ax, cx
|
|
add ax, [prog+0x00E] ; reserved sectors
|
|
mov si, ax
|
|
|
|
; calculate sector offset of target track
|
|
mov ax, [prog+0x018] ; sectors per track
|
|
mul word [prog+0x01A] ; number of heads
|
|
mul word [track]
|
|
|
|
; calculate cluster offset of target track -> SI
|
|
sub ax, si
|
|
mov bl, [prog+0x00D] ; sectors per cluster
|
|
mov bh, 0
|
|
xor dx, dx
|
|
div bx
|
|
mov si, ax
|
|
|
|
; calculate cluster length of target track -> DI
|
|
mov ax, [prog+0x018] ; sectors per track
|
|
add ax, dx ; remainder
|
|
; add sectors per cluster minus one
|
|
add ax, bx
|
|
dec ax
|
|
; divide by sectors per cluster and floor
|
|
xor dx, dx
|
|
div bx
|
|
mov di, ax
|
|
|
|
; load fat table
|
|
call debug
|
|
|
|
ret
|
|
|
|
; TODO:
|
|
; calculate offset into fat table
|
|
; check that all relevant clusters are 0 or 0xFFF7
|
|
; set all relevant clusters to 0xFFF7
|
|
; track is now available for direct writing
|
|
|
|
; set up boot code
|
|
mov di, prog
|
|
mov ax, 0x7FEB
|
|
stosw
|
|
mov byte [di], 0x80
|
|
add di, 0x7F - b_ld + b_rst
|
|
mov si, b_rst
|
|
mov cx, b_end - b_rst
|
|
rep movsb
|
|
|
|
; write back bootsector
|
|
mov ax, 0x0301
|
|
mov cx, 0x0001
|
|
mov dh, 0
|
|
mov bx, prog
|
|
int 0x13
|
|
jc drverr
|
|
|
|
mov dx, fcb1
|
|
mov ah, 0xF
|
|
int 0x21
|
|
test al, al
|
|
jz .fok
|
|
.ferr call putsh
|
|
db "Failed to read input file", 0x0A, 0x0D, 0
|
|
ret
|
|
.fok mov si, prog
|
|
; apply our target address
|
|
.rloop mov dx, si
|
|
mov ah, 0x1A
|
|
int 0x21
|
|
; increment address for next iteration
|
|
add si, 0x80
|
|
; do a read
|
|
mov dx, fcb1
|
|
mov ah, 0x14
|
|
int 0x21
|
|
; success: continue
|
|
cmp al, 0
|
|
jz .rloop
|
|
; eof: break
|
|
cmp al, 1
|
|
jz .cok
|
|
; segment wrap: fail
|
|
cmp al, 2
|
|
jz .ferr
|
|
; we assume al=3: eof
|
|
.cok nop
|
|
mov ax, si
|
|
sub ax, args
|
|
add ax, 0x1FF
|
|
mov cl, 9
|
|
shr ax, cl
|
|
call debug
|
|
|
|
ret
|
|
|
|
; code to copy into boot sector
|
|
b_rst mov ah, 0
|
|
int 0x13
|
|
b_ld mov ax, 0x60
|
|
mov ds, ax
|
|
mov es, ax
|
|
mov ss, ax
|
|
xor sp, sp
|
|
mov ax, 0x0208 ; read, 8 sectors
|
|
b_len equ $ - 2
|
|
mov cx, 0x2701 ; track 39, sector 1
|
|
b_trck equ $ - 1
|
|
b_strt equ $ - 2
|
|
mov dh, 0 ; head 0
|
|
xor bx, bx ; es:bx=0x60:0
|
|
int 0x13
|
|
jc b_rst
|
|
mov byte [4], dl
|
|
jmp 0x60:0x100
|
|
b_end equ $
|
|
|
|
align 2
|
|
psp equ $
|
|
args equ psp + 0x80
|
|
prog equ psp + 0x100
|