boot.s revision 64190 
1# Copyright (c) KATO Takenori, 1999, 2000.
2#
3# All rights reserved.  Unpublished rights reserved under the copyright
4# laws of Japan.
5#
6# Redistribution and use in source and binary forms, with or without
7# modification, are permitted provided that the following conditions
8# are met:
9#
10# 1. Redistributions of source code must retain the above copyright
11#    notice, this list of conditions and the following disclaimer as
12#    the first lines of this file unmodified.
13# 2. Redistributions in binary form must reproduce the above copyright
14#    notice, this list of conditions and the following disclaimer in the
15#    documentation and/or other materials provided with the distribution.
16#
17# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27#
28# $FreeBSD: head/sys/boot/pc98/boot0.5/boot.s 64190 2000-08-03 13:01:45Z kato $
29#
30
31	.code16
32
33	.text
34	.global	boot
35#
36# Read bootstrap program and jump to it.
37#
38boot:
39	# Step 1: Save parameters
40	movw	curdevice, %si
41	movb	daua(%si), %al
42	movb	%al, b_daua
43	shlw	%si
44	movw	secsize(%si), %ax
45	movw	%ax, b_secsize
46
47	movw	curpartition, %si
48	movb	partnum(%si), %al	# %al = real partition number
49	xorb	%ah, %ah
50	movw	%ax, b_partn		# save real parttion number
51	movb	$5, %cl
52	shlw	%cl, %si		# %si = offset to parttable
53	addw	$4, %si
54	movb	parttable(%si), %al	# IPLS
55	movb	%al, b_sector
56	incw	%si
57	movb	parttable(%si), %al	# IPLH
58	movb	%al, b_head
59	incw	%si			# IPLC
60	movw	parttable(%si), %ax
61	movw	%ax, b_cylinder
62
63	# Step 2: Calculate egment address of bootstrap routine
64	movw	$0x1d00, %ax
65	movw	b_secsize, %cx
66	shrw	%cx
67	shrw	%cx
68	subw	%cx, %ax
69	subw	$0x100, %ax
70	movw	%ax, b_bootseg
71
72	# Step 3: Read bootstrap code
73	movb	$6, %ah
74	movb	b_daua, %al
75	movw	b_secsize, %bx
76	shlw	%bx			# 2 sectors
77	movw	b_cylinder, %cx
78	movb	b_head, %dh
79	movb	b_sector, %dl
80	movw	b_bootseg, %es
81	xorw	%bp, %bp
82	int	$0x1b
83	jc	boot_error
84
85	# Step 4: Set DA/UA into BIOS work area
86	xorw	%ax, %ax
87	movw	%ax, %es
88	movw	$0x584, %bx		# DISK_BOOT
89	movb	b_daua, %dl
90	call	write_biosparam
91
92	call	sc_clean
93	# Step 5: Set registers
94	#	%ah:	00
95	#	%al:	DA/UA
96	#	%bx:	Sector size * 2
97	#	%cx:	cylinder number of boot partition
98	#	%si:	pointer to partition table
99	movw	b_partn, %ax
100	movb	$5, %cl
101	shl	%cl, %ax		# %ax = partition number * 32
102	addw	b_secsize, %ax
103	movw	%ax, %si		# %si = pointer to partition table
104	movw	b_cylinder, %cx		# %cx = cylinder
105	movb	b_head, %dh		# %dh = head
106	movb	b_sector, %dl		# %dl = sector
107	movw	b_bootseg, %es		# %es = boot segment
108	movb	b_daua, %al		# %al = DA/UA
109	movw	b_secsize, %bx
110	shlw	%bx			# %bx = sector size * 2
111	cli
112	movw	%cs:iniss, %ss		# Restore stack pointer
113	movw	%cs:inisp, %sp
114	push	%es			# Boot segment
115	xorw	%bp, %bp
116	push	%bp			# 0
117	movw	%ax, %di		# Save %ax
118	xorw	%ax, %ax
119	movw	%ax, %ds		# %ds = 0
120	movw	%di, %ax		# Restore %ax
121	xorb	%ah, %ah		# %ah = 0
122	xorw	%di, %di		# %di = 0
123	sti
124
125	# Jump to bootstrap code
126	lret
127	# NOTREACHED
128
129boot_error:
130	ret
131
132#
133# Try to boot from default partition.
134#
135	.global	trydefault
136trydefault:
137	movw	ndevice, %cx
138	xorw	%si, %si
139trydefault_loop:
140	movw	%si, curdevice
141	push	%cx
142	push	%si
143	call	read_ipl
144	pop	%si
145	pop	%cx
146	cmpb	$0x80, defpartflag
147	jne	nodefpart
148	# Default partition is defined.
149	push	%cx
150	movw	npartition, %cx
151srch_part:
152	movw	%cx, %bx
153	decw	%bx
154	movb	defpartnum, %al		# %al = real partition number
155	cmpb	partnum(%bx), %al
156	jne	not_match
157	movw	%bx, curpartition	# Store partition number
158	call	boot
159not_match:
160	loop	srch_part
161	pop	%cx
162nodefpart:
163	incw	%si
164	loop	trydefault_loop
165	ret
166
167	.data
168b_daua:		.byte	0		# DA/UA
169b_head:		.byte	0		# SYSH
170b_sector:	.byte	0		# SYSS
171b_cylinder:	.word	0		# SYSC
172b_bootseg:	.word	0
173b_secsize:	.word	0
174b_partn:	.word	0		# Real partition number
175