-/* This file is derived from source code used in MIT's 6.828
- course. The original copyright notice is reproduced in full
- below. */
-
-/*
- * Copyright (C) 1997 Massachusetts Institute of Technology
- *
- * This software is being provided by the copyright holders under the
- * following license. By obtaining, using and/or copying this software,
- * you agree that you have read, understood, and will comply with the
- * following terms and conditions:
- *
- * Permission to use, copy, modify, distribute, and sell this software
- * and its documentation for any purpose and without fee or royalty is
- * hereby granted, provided that the full text of this NOTICE appears on
- * ALL copies of the software and documentation or portions thereof,
- * including modifications, that you make.
- *
- * THIS SOFTWARE IS PROVIDED "AS IS," AND COPYRIGHT HOLDERS MAKE NO
- * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED. BY WAY OF EXAMPLE,
- * BUT NOT LIMITATION, COPYRIGHT HOLDERS MAKE NO REPRESENTATIONS OR
- * WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR
- * THAT THE USE OF THE SOFTWARE OR DOCUMENTATION WILL NOT INFRINGE ANY
- * THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS. COPYRIGHT
- * HOLDERS WILL BEAR NO LIABILITY FOR ANY USE OF THIS SOFTWARE OR
- * DOCUMENTATION.
- *
- * The name and trademarks of copyright holders may NOT be used in
- * advertising or publicity pertaining to the software without specific,
- * written prior permission. Title to copyright in this software and any
- * associated documentation will at all times remain with copyright
- * holders. See the file AUTHORS which should have accompanied this software
- * for a list of all copyright holders.
- *
- * This file may be derived from previously copyrighted software. This
- * copyright applies only to those changes made by the copyright
- * holders listed in the AUTHORS file. The rest of this file is covered by
- * the copyright notices, if any, listed below.
- */
-
#include "threads/loader.h"
.intel_syntax noprefix
#### Kernel loader.
-#### This code should be stored in the first sector of the hard disk.
-#### When the BIOS runs, it loads this code at physical address
-#### 0x7c00-0x7e00 (512 bytes). Then it jumps to the beginning of it,
-#### in real mode. This code switches into protected mode (32-bit
-#### mode) so that all of memory can accessed, loads the kernel into
-#### memory, and jumps to the first byte of the kernel, where start.S
-#### is linked.
-
-/* Flags in control register 0. */
-#define CR0_PE 0x00000001 /* Protection Enable. */
-#define CR0_EM 0x00000004 /* (Floating-point) Emulation. */
-#define CR0_PG 0x80000000 /* Paging. */
-#define CR0_WP 0x00010000 /* Write-Protect enable in kernel mode. */
-
-# Code runs in real mode, which is a 16-bit segment.
-
-.globl start
-start:
+# Runs in real mode, which is a 16-bit segment.
.code16
# Set up segment registers.
# Stack grows downward starting from us.
+.globl start
+start:
sub ax, ax
mov ds, ax
mov ss, ax
mov sp, 0x7c00
-
+ cld
+
+ mov ax, 0x00e3
+ sub dx, dx
+ int 0x14
+
# Scan floppy disks.
sub dl, dl
# Scan hard disks.
mov dl, 0x80
-1: call scan_partitions
+1: call outw
+ call scan_partitions
inc dl
jnc 1b
- call panic
- .asciz "No boot partition"
+1: jmp 1b
scan_partitions:
# EBX = sector number of partition table
# DL = drive number
# ES:0000 -> buffer for partition table
- # Returns CF set if drive exists, CF clear otherwise.
+ # Returns CF set if drive does not exist, CF clear otherwise.
call read_sector
- jnc no_such_drive
-2: cmp word ptr [es:510], 0xaa55
+ jc no_such_drive
+
+2: pusha
+ mov edx, [es:508]
+ call outw
+ popa
+
+ cmp word ptr [es:510], 0xaa55
jnz no_boot_partition
mov si, 446
# returns error flag in CF
read_sector:
pusha
- or dl, dl # Floppy drives: DL < 0
- js read_floppy_sector
+ or dl, dl # Floppy drives: DL >= 0
+ jns read_floppy_sector
read_harddrv_sector:
sub eax, eax
push eax # LBA sector number [32:63]
push ebx # LBA sector number [0:31]
- mov ax, es
- shl eax, 4
- push eax # Buffer linear address
+ push es
+ push 0
push 1 # Transfer one sector
push 16 # Packet size
mov ah, 0x42 # Extended read
mov si, sp # DS:SI -> packet
int 0x13 # Error code in CF
-success:
+ lahf
+ add sp, 16
+ sahf
+read_sector_done:
popa
ret # Error code in CF
mov dl, bl # DL = drive
mov ax, 0x0201 # AH = function, AL = sectors to read
sub bx, bx # ES:BX -> buffer
+ mov di, 3 # Number of tries left.
+
+try_read_floppy:
pusha
int 0x13
popa
- jnc success
+ jnc read_sector_done
+ dec di
+ jnz 1f
+ stc
+ jmp read_sector_done
- # Reset floppy drive motor, try again.
+1: # Reset floppy drive motor, try again.
+ pusha
sub ah, ah
int 0x13
popa
- jmp read_sector
+ jmp try_read_floppy
+
+outw: pushf
+ pusha
+
+ mov cx, 8
+ mov ebx, edx
+ mov dx, 0xe9
+1: rol ebx, 4
+ mov al, bl
+ and al, 15
+ add al, '0'
+ cmp al, '9'
+ jbe 2f
+ add al, 'a' - '0' - 10
+2: out dx, al
+ loop 1b
+
+ mov al, '\n'
+ out dx, al
+
+ popa
+ popf
+ ret
#### The partition table goes here.
.org 446
-part_tbl:
+part_tbl:
+
#### Boot-sector signature for BIOS inspection.
.org 510
projects / pintos-anon / commitdiff