1/*
2 * Copyright (c) 1998 Robert Nordier
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
8 * such forms.
9 *
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
13 * purpose.
14 *
15 * $FreeBSD$
16 */
17
18/* Memory Locations */
19		.set MEM_ARG,0x900		# Arguments
20		.set MEM_ORG,0x7c00		# Origin
21		.set MEM_BUF,0x8000		# Load area
22		.set MEM_BTX,0x9000		# BTX start
23		.set MEM_JMP,0x9010		# BTX entry point
24		.set MEM_USR,0xa000		# Client start
25		.set BDA_BOOT,0x472		# Boot howto flag
26
27/* Partition Constants */
28		.set PRT_OFF,0x1be		# Partition offset
29		.set PRT_NUM,0x4		# Partitions
30		.set PRT_BSD,0xa5		# Partition type
31
32/* Misc. Constants */
33		.set SIZ_PAG,0x1000		# Page size
34		.set SIZ_SEC,0x200		# Sector size
35
36		.set NSECT,0x80
37		.globl start
38		.code16
39
40/*
41 * Load the rest of zfsboot2 and BTX up, copy the parts to the right locations,
42 * and start it all up.
43 */
44
45/*
46 * Setup the segment registers to flat addressing (segment 0) and setup the
47 * stack to end just below the start of our code.
48 */
49start:		cld				# String ops inc
50		xor %cx,%cx			# Zero
51		mov %cx,%es			# Address
52		mov %cx,%ds			#  data
53		mov %cx,%ss			# Set up
54		mov $start,%sp			#  stack
55/*
56 * Load the MBR and look for the first FreeBSD slice.  We use the fake
57 * partition entry below that points to the MBR when we call read.
58 * The first pass looks for the first active FreeBSD slice.  The
59 * second pass looks for the first non-active FreeBSD slice if the
60 * first one fails.
61 */
62		call check_edd		 	# Make sure EDD works
63		mov $part4,%si			# Dummy partition
64		xor %eax,%eax			# Read MBR
65		movl $MEM_BUF,%ebx		#  from first
66		call read			#  sector
67		mov $0x1,%cx	 		# Two passes
68main.1: 	mov $MEM_BUF+PRT_OFF,%si	# Partition table
69		movb $0x1,%dh			# Partition
70main.2: 	cmpb $PRT_BSD,0x4(%si)		# Our partition type?
71		jne main.3			# No
72		jcxz main.5			# If second pass
73		testb $0x80,(%si)		# Active?
74		jnz main.5			# Yes
75main.3: 	add $0x10,%si	 		# Next entry
76		incb %dh			# Partition
77		cmpb $0x1+PRT_NUM,%dh		# In table?
78		jb main.2			# Yes
79		dec %cx				# Do two
80		jcxz main.1			#  passes
81/*
82 * If we get here, we didn't find any FreeBSD slices at all, so print an
83 * error message and die.
84 */
85		mov $msg_part,%si		# Message
86		jmp error			# Error
87
88/*
89 * Ok, we have a slice and drive in %dx now, so use that to locate and
90 * load boot2.  %si references the start of the slice we are looking
91 * for, so go ahead and load up the 128 sectors starting at sector 1024
92 * (i.e. after the two vdev labels).  We don't have do anything fancy
93 * here to allow for an extra copy of boot1 and a partition table
94 * (compare to this section of the UFS bootstrap) so we just load it
95 * all at 0x9000. The first part of boot2 is BTX, which wants to run
96 * at 0x9000. The boot2.bin binary starts right after the end of BTX,
97 * so we have to figure out where the start of it is and then move the
98 * binary to 0xc000.  Normally, BTX clients start at MEM_USR, or 0xa000,
99 * but when we use btxld to create zfsboot2, we use an entry point of
100 * 0x2000.  That entry point is relative to MEM_USR; thus boot2.bin
101 * starts at 0xc000.
102 *
103 * The load area and the target area for the client overlap so we have
104 * to use a decrementing string move. We also play segment register
105 * games with the destination address for the move so that the client
106 * can be larger than 16k (which would overflow the zero segment since
107 * the client starts at 0xc000).
108 */
109main.5: 	mov %dx,MEM_ARG			# Save args
110		mov $NSECT,%cx			# Sector count
111		movl $1024,%eax			# Offset to boot2
112		mov $MEM_BTX,%ebx		# Destination buffer
113main.6:		pushal				# Save params
114		call read			# Read disk
115		popal				# Restore
116		incl %eax			# Advance to
117		add $SIZ_SEC,%ebx		#  next sector
118		loop main.6			# If not last, read another
119		mov MEM_BTX+0xa,%bx		# Get BTX length
120		mov $NSECT*SIZ_SEC-1,%di	# Size of load area (less one)
121		mov %di,%si			# End of load area, 0x9000 rel
122		sub %bx,%di			# End of client, 0xc000 rel
123		mov %di,%cx			# Size of
124		inc %cx				#  client
125		mov $(MEM_BTX)>>4,%dx		# Segment
126		mov %dx,%ds			#   addressing 0x9000
127		mov $(MEM_USR+2*SIZ_PAG)>>4,%dx	# Segment
128		mov %dx,%es			#   addressing 0xc000
129		std				# Move with decrement
130		rep				# Relocate
131		movsb				#  client
132		cld				# Back to increment
133		xor %dx,%dx			# Back
134		mov %ds,%dx			#  to zero
135		mov %dx,%es			#  segment
136
137/*
138 * Enable A20 so we can access memory above 1 meg.
139 * Use the zero-valued %cx as a timeout for embedded hardware which do not
140 * have a keyboard controller.
141 */
142seta20: 	cli				# Disable interrupts
143seta20.1:	dec %cx				# Timeout?
144		jz seta20.3			# Yes
145		inb $0x64,%al			# Get status
146		testb $0x2,%al			# Busy?
147		jnz seta20.1			# Yes
148		movb $0xd1,%al			# Command: Write
149		outb %al,$0x64			#  output port
150seta20.2:	inb $0x64,%al			# Get status
151		testb $0x2,%al			# Busy?
152		jnz seta20.2			# Yes
153		movb $0xdf,%al			# Enable
154		outb %al,$0x60			#  A20
155seta20.3:	sti				# Enable interrupts
156
157		jmp start+MEM_JMP-MEM_ORG	# Start BTX
158
159
160/*
161 * Read a sector from the disk.  Sets up an EDD packet on the stack
162 * and passes it to read.  We assume that the destination address is
163 * always segment-aligned.
164 *
165 * %eax		- int     - LBA to read in relative to partition start
166 * %ebx		- ptr	  - destination address
167 * %dl		- byte    - drive to read from
168 * %si		- ptr     - MBR partition entry
169 */
170read:		xor %ecx,%ecx			# Get
171		addl 0x8(%si),%eax		#  LBA
172		adc $0,%ecx
173		pushl %ecx			# Starting absolute block
174		pushl %eax			#  block number
175		shr $4,%ebx			# Convert to segment
176		push %bx			# Address of
177		push $0				#  transfer buffer
178		push $0x1			# Read 1 sector
179		push $0x10			# Size of packet
180		mov %sp,%si			# Packet pointer
181		mov $0x42,%ah			# BIOS: Extended
182		int $0x13			#  read
183		jc read.1			# If error, fail
184		lea 0x10(%si),%sp		# Clear stack
185		ret				# If success, return
186read.1:		mov %ah,%al			# Format
187		mov $read_err,%di		#  error
188		call hex8			#  code
189		mov $msg_read,%si		# Set the error message and
190						#  fall through to the error
191						#  routine
192/*
193 * Print out the error message pointed to by %ds:(%si) followed
194 * by a prompt, wait for a keypress, and then reboot the machine.
195 */
196error:		callw putstr			# Display message
197		mov $prompt,%si			# Display
198		callw putstr			#  prompt
199		xorb %ah,%ah			# BIOS: Get
200		int $0x16			#  keypress
201		movw $0x1234, BDA_BOOT		# Do a warm boot
202		ljmp $0xffff,$0x0		# reboot the machine
203/*
204 * Display a null-terminated string using the BIOS output.
205 */
206putstr.0:	mov $0x7,%bx	 		# Page:attribute
207		movb $0xe,%ah			# BIOS: Display
208		int $0x10			#  character
209putstr: 	lodsb				# Get char
210		testb %al,%al			# End of string?
211		jne putstr.0			# No
212		ret				# To caller
213/*
214 * Check to see if the disk supports EDD.  zfsboot requires EDD and does not
215 * support older C/H/S disk I/O.
216 */
217check_edd:	cmpb $0x80,%dl			# Hard drive?
218		jb check_edd.1 			# No, fail to boot
219		mov $0x55aa,%bx			# Magic
220		push %dx			# Save
221		movb $0x41,%ah			# BIOS: Check
222		int $0x13			#  extensions present
223		pop %dx				# Restore
224		jc check_edd.1			# If error, fail
225		cmp $0xaa55,%bx			# Magic?
226		jne check_edd.1			# No, so fail
227		testb $0x1,%cl			# Packet interface?
228		jz check_edd.1			# No, so fail
229		ret				# EDD ok, keep booting
230check_edd.1:	mov $msg_chs,%si		# Warn that CHS is
231		jmp error			#  unsupported and fail
232/*
233 * AL to hex, saving the result to [EDI].
234 */
235hex8:		push %ax			# Save
236		shrb $0x4,%al			# Do upper
237		call hex8.1			#  4
238		pop %ax				# Restore
239hex8.1: 	andb $0xf,%al			# Get lower 4
240		cmpb $0xa,%al			# Convert
241		sbbb $0x69,%al			#  to hex
242		das				#  digit
243		orb $0x20,%al			# To lower case
244		stosb				# Save char
245		ret				# (Recursive)
246
247/* Messages */
248
249msg_chs:	.asciz "CHS not supported"
250msg_read:	.ascii "Read error: "
251read_err:	.asciz "XX"
252msg_part:	.asciz "Boot error"
253
254prompt: 	.asciz "\r\n"
255
256		.org PRT_OFF,0x90
257
258/* Partition table */
259
260		.fill 0x30,0x1,0x0
261part4:		.byte 0x80, 0x00, 0x01, 0x00
262		.byte 0xa5, 0xfe, 0xff, 0xff
263		.byte 0x00, 0x00, 0x00, 0x00
264		.byte 0x50, 0xc3, 0x00, 0x00	# 50000 sectors long, bleh
265
266		.word 0xaa55			# Magic number
267