mirror of https://github.com/FDOS/kernel.git
393 lines
12 KiB
NASM
393 lines
12 KiB
NASM
; +--------+
|
|
; | |
|
|
; | |
|
|
; |--------| 4000:0000
|
|
; | |
|
|
; | FAT |
|
|
; | |
|
|
; |--------| 2000:0000
|
|
; |BOOT SEC|
|
|
; |RELOCATE|
|
|
; |--------| 1FE0:0000
|
|
; | |
|
|
; | |
|
|
; | |
|
|
; | |
|
|
; |--------|
|
|
; |BOOT SEC|
|
|
; |ORIGIN | 07C0:0000
|
|
; |--------|
|
|
; | |
|
|
; | |
|
|
; | |
|
|
; |--------|
|
|
; |KERNEL |
|
|
; |LOADED |
|
|
; |--------| 0060:0000
|
|
; | |
|
|
; +--------+
|
|
|
|
;%define MULTI_SEC_READ 1
|
|
|
|
|
|
segment .text
|
|
|
|
%define BASE 0x7c00
|
|
|
|
org BASE
|
|
|
|
Entry: jmp short real_start
|
|
nop
|
|
|
|
; bp is initialized to 7c00h
|
|
%define bsOemName bp+0x03 ; OEM label
|
|
%define bsBytesPerSec bp+0x0b ; bytes/sector
|
|
%define bsSecPerClust bp+0x0d ; sectors/allocation unit
|
|
%define bsResSectors bp+0x0e ; # reserved sectors
|
|
%define bsFATs bp+0x10 ; # of fats
|
|
%define bsRootDirEnts bp+0x11 ; # of root dir entries
|
|
%define bsSectors bp+0x13 ; # sectors total in image
|
|
%define bsMedia bp+0x15 ; media descrip: fd=2side9sec, etc...
|
|
%define sectPerFat bp+0x16 ; # sectors in a fat
|
|
%define sectPerTrack bp+0x18 ; # sectors/track
|
|
%define nHeads bp+0x1a ; # heads
|
|
%define nHidden bp+0x1c ; # hidden sectors
|
|
%define nSectorHuge bp+0x20 ; # sectors if > 65536
|
|
%define xsectPerFat bp+0x24 ; Sectors/Fat
|
|
%define xrootClst bp+0x2c ; Starting cluster of root directory
|
|
%define drive bp+0x40 ; Drive number
|
|
|
|
times 0x5a-$+$$ db 0
|
|
|
|
%define LOADSEG 0x0060
|
|
|
|
%define FATSEG 0x2000
|
|
|
|
%define fat_sector bp+0x48 ; last accessed sector of the FAT
|
|
|
|
%define loadsegoff_60 bp+loadseg_off-Entry ; FAR pointer = 60:0
|
|
%define loadseg_60 bp+loadseg_seg-Entry
|
|
|
|
%define fat_start bp+0x5e ; first FAT sector
|
|
%define data_start bp+0x62 ; first data sector
|
|
%define fat_secmask bp+0x66 ; number of clusters in a FAT sector - 1
|
|
%define fat_secshift bp+0x68 ; fat_secmask+1 = 2^fat_secshift
|
|
|
|
;-----------------------------------------------------------------------
|
|
; ENTRY
|
|
;-----------------------------------------------------------------------
|
|
|
|
real_start: cld
|
|
cli
|
|
sub ax, ax
|
|
mov ds, ax
|
|
mov bp, 0x7c00
|
|
|
|
mov ax, 0x1FE0
|
|
mov es, ax
|
|
mov si, bp
|
|
mov di, bp
|
|
mov cx, 0x0100
|
|
rep movsw ; move boot code to the 0x1FE0:0x0000
|
|
jmp word 0x1FE0:cont
|
|
|
|
loadseg_off dw 0
|
|
loadseg_seg dw LOADSEG
|
|
|
|
cont: mov ds, ax
|
|
mov ss, ax
|
|
lea sp, [bp-0x20]
|
|
sti
|
|
mov [drive], dl ; BIOS passes drive number in DL
|
|
|
|
; call print
|
|
; db "Loading ",0
|
|
|
|
; Calc Params
|
|
; Fat_Start
|
|
mov si, word [nHidden]
|
|
mov di, word [nHidden+2]
|
|
add si, word [bsResSectors]
|
|
adc di, byte 0
|
|
|
|
mov word [fat_start], si
|
|
mov word [fat_start+2], di
|
|
; Data_Start
|
|
mov al, [bsFATs]
|
|
cbw
|
|
push ax
|
|
mul word [xsectPerFat+2]
|
|
add di, ax
|
|
pop ax
|
|
mul word [xsectPerFat]
|
|
add ax, si
|
|
adc dx, di
|
|
mov word[data_start], ax
|
|
mov word[data_start+2], dx
|
|
; fat_secmask
|
|
mov ax, word[bsBytesPerSec]
|
|
shr ax, 1
|
|
shr ax, 1
|
|
dec ax
|
|
mov word [fat_secmask], ax
|
|
; fat_secshift
|
|
; cx = temp
|
|
; ax = fat_secshift
|
|
xchg ax, cx ; cx = 0 after movsw
|
|
inc cx
|
|
secshift: inc ax
|
|
shr cx, 1
|
|
cmp cx, 1
|
|
jne secshift
|
|
mov byte [fat_secshift], al
|
|
dec cx
|
|
|
|
; FINDFILE: Searches for the file in the root directory.
|
|
;
|
|
; Returns:
|
|
; DX:AX = first cluster of file
|
|
|
|
mov word [fat_sector], cx ; CX is 0 after "dec"
|
|
mov word [fat_sector + 2], cx
|
|
|
|
mov ax, word [xrootClst]
|
|
mov dx, word [xrootClst + 2]
|
|
ff_next_cluster:
|
|
push dx ; save cluster
|
|
push ax
|
|
call convert_cluster
|
|
jc boot_error ; EOC encountered
|
|
|
|
ff_next_sector:
|
|
push bx ; save sector count
|
|
|
|
les bx, [loadsegoff_60]
|
|
call readDisk
|
|
push dx ; save sector
|
|
push ax
|
|
|
|
mov ax, [bsBytesPerSec]
|
|
|
|
; Search for KERNEL.SYS file name, and find start cluster.
|
|
ff_next_entry: mov cx, 11
|
|
mov si, filename
|
|
mov di, ax
|
|
sub di, 0x20
|
|
repe cmpsb
|
|
jz ff_done
|
|
|
|
sub ax, 0x20
|
|
jnz ff_next_entry
|
|
pop ax ; restore sector
|
|
pop dx
|
|
pop bx ; restore sector count
|
|
dec bx
|
|
jnz ff_next_sector
|
|
ff_find_next_cluster:
|
|
pop ax ; restore current cluster
|
|
pop dx
|
|
call next_cluster
|
|
jmp short ff_next_cluster
|
|
ff_done:
|
|
|
|
mov ax, [es:di+0x1A-11] ; get cluster number
|
|
mov dx, [es:di+0x14-11]
|
|
c4:
|
|
sub bx, bx ; ES points to LOADSEG
|
|
c5: push dx
|
|
push ax
|
|
push bx
|
|
call convert_cluster
|
|
jc boot_success
|
|
mov di, bx
|
|
pop bx
|
|
c6:
|
|
call readDisk
|
|
dec di
|
|
jnz c6
|
|
pop ax
|
|
pop dx
|
|
call next_cluster
|
|
jmp short c5
|
|
|
|
boot_error:
|
|
xor ah,ah
|
|
int 0x16 ; wait for a key
|
|
int 0x19 ; reboot the machine
|
|
|
|
; input:
|
|
; DX:AX - cluster
|
|
; output:
|
|
; DX:AX - next cluster
|
|
; CX = 0
|
|
; modify:
|
|
; DI
|
|
next_cluster:
|
|
push es
|
|
mov di, ax
|
|
and di, [fat_secmask]
|
|
|
|
mov cx, [fat_secshift]
|
|
cn_loop:
|
|
shr dx,1
|
|
rcr ax,1
|
|
dec cx
|
|
jnz cn_loop ; DX:AX fat sector where our
|
|
; cluster resides
|
|
; DI - cluster index in this
|
|
; sector
|
|
|
|
shl di,1 ; DI - offset in the sector
|
|
shl di,1
|
|
add ax, [fat_start]
|
|
adc dx, [fat_start+2] ; DX:AX absolute fat sector
|
|
|
|
push bx
|
|
mov bx, FATSEG
|
|
mov es, bx
|
|
sub bx, bx
|
|
|
|
cmp ax, [fat_sector]
|
|
jne cn1 ; if the last fat sector we
|
|
; read was this, than skip
|
|
cmp dx,[fat_sector+2]
|
|
je cn_exit
|
|
cn1:
|
|
mov [fat_sector],ax ; save the fat sector number,
|
|
mov [fat_sector+2],dx ; we are going to read
|
|
call readDisk
|
|
cn_exit:
|
|
pop bx
|
|
mov ax, [es:di] ; DX:AX - next cluster
|
|
mov dx, [es:di + 2] ;
|
|
pop es
|
|
ret
|
|
|
|
|
|
boot_success:
|
|
mov bl, [drive]
|
|
jmp far [loadsegoff_60]
|
|
|
|
; Convert cluster to the absolute sector
|
|
;input:
|
|
; DX:AX - target cluster
|
|
;output:
|
|
; DX:AX - absoulute sector
|
|
; BX - [bsSectPerClust]
|
|
;modify:
|
|
; CX
|
|
convert_cluster:
|
|
cmp dx,0x0fff
|
|
jne c3
|
|
cmp ax,0xfff8
|
|
jb c3 ; if cluster is EOC (carry is set), do ret
|
|
stc
|
|
ret
|
|
c3:
|
|
mov cx, dx ; sector = (cluster - 2)*clussize +
|
|
; + data_start
|
|
sub ax, 2
|
|
sbb cx, byte 0 ; CX:AX == cluster - 2
|
|
mov bl, [bsSecPerClust]
|
|
sub bh, bh
|
|
xchg cx, ax ; AX:CX == cluster - 2
|
|
mul bx ; first handle high word
|
|
; DX must be 0 here
|
|
xchg ax, cx ; then low word
|
|
mul bx
|
|
add dx, cx ; DX:AX target sector
|
|
add ax, [data_start]
|
|
adc dx, [data_start + 2]
|
|
ret
|
|
|
|
; prints text after call to this function.
|
|
|
|
print_1char:
|
|
xor bx, bx ; video page 0
|
|
mov ah, 0x0E ; else print it
|
|
int 0x10 ; via TTY mode
|
|
print: pop si ; this is the first character
|
|
print1: lodsb ; get token
|
|
push si ; stack up potential return address
|
|
cmp al, 0 ; end of string?
|
|
jne print_1char ; until done
|
|
ret ; and jump to it
|
|
|
|
;input:
|
|
; DX:AX - 32-bit DOS sector number
|
|
; ES:BX - destination buffer
|
|
;output:
|
|
; ES:BX points one byte after the last byte read.
|
|
; DX:AX - next sector
|
|
;modify:
|
|
; ES if DI * bsBytesPerSec >= 65536, CX
|
|
|
|
readDisk:
|
|
read_next: push dx
|
|
push ax
|
|
;
|
|
; translate sector number to BIOS parameters
|
|
;
|
|
|
|
;
|
|
; abs = sector offset in track
|
|
; + head * sectPerTrack offset in cylinder
|
|
; + track * sectPerTrack * nHeads offset in platter
|
|
;
|
|
xchg ax, cx
|
|
mov al, [sectPerTrack]
|
|
mul byte [nHeads]
|
|
xchg ax, cx
|
|
; cx = nHeads * sectPerTrack <= 255*63
|
|
; dx:ax = abs
|
|
div cx
|
|
; ax = track, dx = sector + head * sectPertrack
|
|
xchg ax, dx
|
|
; dx = track, ax = sector + head * sectPertrack
|
|
div byte [sectPerTrack]
|
|
; dx = track, al = head, ah = sector
|
|
mov cx, dx
|
|
; cx = track, al = head, ah = sector
|
|
|
|
; the following manipulations are necessary in order to
|
|
; properly place parameters into registers.
|
|
; ch = cylinder number low 8 bits
|
|
; cl = 7-6: cylinder high two bits
|
|
; 5-0: sector
|
|
mov dh, al ; save head into dh for bios
|
|
xchg ch, cl ; set cyl no low 8 bits
|
|
ror cl, 1 ; move track high bits into
|
|
ror cl, 1 ; bits 7-6 (assumes top = 0)
|
|
inc ah ; sector offset from 1
|
|
or cl, ah ; merge sector into cylinder
|
|
|
|
mov ax, 0x0201
|
|
mov dl, [drive]
|
|
int 0x13
|
|
|
|
pop ax
|
|
pop dx
|
|
jnc read_ok ; jump if no error
|
|
xor ah, ah ; else, reset floppy
|
|
int 0x13
|
|
jmp short read_next
|
|
read_ok:
|
|
add bx, word [bsBytesPerSec]
|
|
|
|
jnc no_incr_es ; if overflow...
|
|
|
|
mov cx, es
|
|
add ch, 0x10 ; ...add 1000h to ES
|
|
mov es, cx
|
|
|
|
no_incr_es:
|
|
add ax,byte 1
|
|
adc dx,byte 0
|
|
ret
|
|
|
|
times 0x01f1-$+$$ db 0
|
|
|
|
filename db "KERNEL SYS",0,0
|
|
|
|
sign dw 0xAA55
|