From 4c537c2ca993e6a980955cfaf1c6dab9788a7f22 Mon Sep 17 00:00:00 2001 From: pumnflqv2 Date: Sun, 26 Jun 2022 21:30:47 +0800 Subject: [PATCH] ADD file via upload --- boot/bootsect.s | 260 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 260 insertions(+) create mode 100644 boot/bootsect.s diff --git a/boot/bootsect.s b/boot/bootsect.s new file mode 100644 index 0000000..711f103 --- /dev/null +++ b/boot/bootsect.s @@ -0,0 +1,260 @@ +! +! 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: