!! 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.textbegtext:.databegdata:.bssbegbss:.textSETUPLEN = 4				! nr of setup-sectorsBOOTSEG  = 0x07c0			! original address of boot-sectorINITSEG  = 0x9000			! we move boot here - out of the waySETUPSEG = 0x9020			! setup starts hereSYSSEG   = 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 etcROOT_DEV = 0x306entry _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,INITSEGgo:	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_setupok_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_definedundef_root:	jmp undef_rootroot_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 trackhead:	.word 0			! current headtrack:	.word 0			! current trackread_it:	mov ax,es	test ax,#0x0fffdie:	jne die			! es must be at 64kB boundary	xor bx,bx		! bx is starting address within segmentrp_read:	mov ax,es	cmp ax,#ENDSEG		! have we loaded all yet?	jb ok1_read	retok1_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,#9ok2_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 trackok4_read:	mov head,ax	xor ax,axok3_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_readread_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	retbad_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	retsectors:	.word 0msg1:	.byte 13,10	.ascii "Loading system ..."	.byte 13,10,13,10.org 508root_dev:	.word ROOT_DEVboot_flag:	.word 0xAA55.textendtext:.dataenddata:.bssendbss: