You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
260 lines
4.9 KiB
260 lines
4.9 KiB
;
|
|
; SYS_SIZE is the number of clicks (16 bytes) to be loaded.
|
|
; 0x3000 is 0x30000 bytes = 196kB, more than enough for current
|
|
; versions of linux
|
|
;
|
|
SYSSIZE = 0x3000
|
|
;
|
|
; bootsect.s (C) 1991 Linus Torvalds
|
|
;
|
|
; bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
|
|
; iself out of the way to address 0x90000, and jumps there.
|
|
;
|
|
; It then loads 'setup' directly after itself (0x90200), and the system
|
|
; at 0x10000, using BIOS interrupts.
|
|
;
|
|
; NOTE; currently system is at most 8*65536 bytes long. This should be no
|
|
; problem, even in the future. I want to keep it simple. This 512 kB
|
|
; kernel size should be enough, especially as this doesn't contain the
|
|
; buffer cache as in minix
|
|
;
|
|
; The loader has been made as simple as possible, and continuos
|
|
; read errors will result in a unbreakable loop. Reboot by hand. It
|
|
; loads pretty fast by getting whole sectors at a time whenever possible.
|
|
|
|
.globl begtext, begdata, begbss, endtext, enddata, endbss
|
|
.text
|
|
begtext:
|
|
.data
|
|
begdata:
|
|
.bss
|
|
begbss:
|
|
.text
|
|
|
|
SETUPLEN = 4 ; nr of setup-sectors
|
|
BOOTSEG = 0x07c0 ; original address of boot-sector
|
|
INITSEG = 0x9000 ; we move boot here - out of the way
|
|
SETUPSEG = 0x9020 ; setup starts here
|
|
SYSSEG = 0x1000 ; system loaded at 0x10000 (65536).
|
|
ENDSEG = SYSSEG + SYSSIZE ; where to stop loading
|
|
|
|
; ROOT_DEV: 0x000 - same type of floppy as boot.
|
|
; 0x301 - first partition on first drive etc
|
|
ROOT_DEV = 0x306
|
|
|
|
entry start
|
|
start:
|
|
mov ax,#BOOTSEG
|
|
mov ds,ax
|
|
mov ax,#INITSEG
|
|
mov es,ax
|
|
mov cx,#256
|
|
sub si,si
|
|
sub di,di
|
|
rep
|
|
movw
|
|
jmpi go,INITSEG
|
|
go: mov ax,cs
|
|
mov ds,ax
|
|
mov es,ax
|
|
; put stack at 0x9ff00.
|
|
mov ss,ax
|
|
mov sp,#0xFF00 ; arbitrary value >>512
|
|
|
|
; load the setup-sectors directly after the bootblock.
|
|
; Note that 'es' is already set up.
|
|
|
|
load_setup:
|
|
mov dx,#0x0000 ; drive 0, head 0
|
|
mov cx,#0x0002 ; sector 2, track 0
|
|
mov bx,#0x0200 ; address = 512, in INITSEG
|
|
mov ax,#0x0200+SETUPLEN ; service 2, nr of sectors
|
|
int 0x13 ; read it
|
|
jnc ok_load_setup ; ok - continue
|
|
mov dx,#0x0000
|
|
mov ax,#0x0000 ; reset the diskette
|
|
int 0x13
|
|
j load_setup
|
|
|
|
ok_load_setup:
|
|
|
|
; Get disk drive parameters, specifically nr of sectors/track
|
|
|
|
mov dl,#0x00
|
|
mov ax,#0x0800 ; AH=8 is get drive parameters
|
|
int 0x13
|
|
mov ch,#0x00
|
|
seg cs
|
|
mov sectors,cx
|
|
mov ax,#INITSEG
|
|
mov es,ax
|
|
|
|
; Print some inane message
|
|
|
|
mov ah,#0x03 ; read cursor pos
|
|
xor bh,bh
|
|
int 0x10
|
|
|
|
mov cx,#24
|
|
mov bx,#0x0007 ; page 0, attribute 7 (normal)
|
|
mov bp,#msg1
|
|
mov ax,#0x1301 ; write string, move cursor
|
|
int 0x10
|
|
|
|
; ok, we've written the message, now
|
|
; we want to load the system (at 0x10000)
|
|
|
|
mov ax,#SYSSEG
|
|
mov es,ax ; segment of 0x010000
|
|
call read_it
|
|
call kill_motor
|
|
|
|
; After that we check which root-device to use. If the device is
|
|
; defined (!= 0), nothing is done and the given device is used.
|
|
; Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
|
|
; on the number of sectors that the BIOS reports currently.
|
|
|
|
seg cs
|
|
mov ax,root_dev
|
|
cmp ax,#0
|
|
jne root_defined
|
|
seg cs
|
|
mov bx,sectors
|
|
mov ax,#0x0208 ; /dev/ps0 - 1.2Mb
|
|
cmp bx,#15
|
|
je root_defined
|
|
mov ax,#0x021c ; /dev/PS0 - 1.44Mb
|
|
cmp bx,#18
|
|
je root_defined
|
|
undef_root:
|
|
jmp undef_root
|
|
root_defined:
|
|
seg cs
|
|
mov root_dev,ax
|
|
|
|
; after that (everyting loaded), we jump to
|
|
; the setup-routine loaded directly after
|
|
; the bootblock:
|
|
|
|
jmpi 0,SETUPSEG
|
|
|
|
; This routine loads the system at address 0x10000, making sure
|
|
; no 64kB boundaries are crossed. We try to load it as fast as
|
|
; possible, loading whole tracks whenever we can.
|
|
;
|
|
; in: es - starting address segment (normally 0x1000)
|
|
;
|
|
sread: .word 1+SETUPLEN ; sectors read of current track
|
|
head: .word 0 ; current head
|
|
track: .word 0 ; current track
|
|
|
|
read_it:
|
|
mov ax,es
|
|
test ax,#0x0fff
|
|
die: jne die ; es must be at 64kB boundary
|
|
xor bx,bx ; bx is starting address within segment
|
|
rp_read:
|
|
mov ax,es
|
|
cmp ax,#ENDSEG ; have we loaded all yet?
|
|
jb ok1_read
|
|
ret
|
|
ok1_read:
|
|
seg cs
|
|
mov ax,sectors
|
|
sub ax,sread
|
|
mov cx,ax
|
|
shl cx,#9
|
|
add cx,bx
|
|
jnc ok2_read
|
|
je ok2_read
|
|
xor ax,ax
|
|
sub ax,bx
|
|
shr ax,#9
|
|
ok2_read:
|
|
call read_track
|
|
mov cx,ax
|
|
add ax,sread
|
|
seg cs
|
|
cmp ax,sectors
|
|
jne ok3_read
|
|
mov ax,#1
|
|
sub ax,head
|
|
jne ok4_read
|
|
inc track
|
|
ok4_read:
|
|
mov head,ax
|
|
xor ax,ax
|
|
ok3_read:
|
|
mov sread,ax
|
|
shl cx,#9
|
|
add bx,cx
|
|
jnc rp_read
|
|
mov ax,es
|
|
add ax,#0x1000
|
|
mov es,ax
|
|
xor bx,bx
|
|
jmp rp_read
|
|
|
|
read_track:
|
|
push ax
|
|
push bx
|
|
push cx
|
|
push dx
|
|
mov dx,track
|
|
mov cx,sread
|
|
inc cx
|
|
mov ch,dl
|
|
mov dx,head
|
|
mov dh,dl
|
|
mov dl,#0
|
|
and dx,#0x0100
|
|
mov ah,#2
|
|
int 0x13
|
|
jc bad_rt
|
|
pop dx
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
ret
|
|
bad_rt: mov ax,#0
|
|
mov dx,#0
|
|
int 0x13
|
|
pop dx
|
|
pop cx
|
|
pop bx
|
|
pop ax
|
|
jmp read_track
|
|
|
|
/*
|
|
* This procedure turns off the floppy drive motor, so
|
|
* that we enter the kernel in a known state, and
|
|
* don't have to worry about it later.
|
|
*/
|
|
kill_motor:
|
|
push dx
|
|
mov dx,#0x3f2
|
|
mov al,#0
|
|
outb
|
|
pop dx
|
|
ret
|
|
|
|
sectors:
|
|
.word 0
|
|
|
|
msg1:
|
|
.byte 13,10
|
|
.ascii "Loading system ..."
|
|
.byte 13,10,13,10
|
|
|
|
.org 508
|
|
root_dev:
|
|
.word ROOT_DEV
|
|
boot_flag:
|
|
.word 0xAA55
|
|
|
|
.text
|
|
endtext:
|
|
.data
|
|
enddata:
|
|
.bss
|
|
endbss:
|