2 * Copyright (c) 2007 Yahoo!, Inc.
4 * Written by: John Baldwin <jhb@FreeBSD.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the author nor the names of any co-contributors
15 * may be used to endorse or promote products derived from this software
16 * without specific prior written permission.
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * Partly from: src/sys/boot/i386/boot2/boot1.S 1.31
35 /* Memory Locations */
36 .set MEM_REL,0x700 # Relocation address
37 .set MEM_ARG,0x900 # Arguments
38 .set MEM_ORG,0x7c00 # Origin
39 .set MEM_BUF,0x8cec # Load area
40 .set MEM_BTX,0x9000 # BTX start
41 .set MEM_JMP,0x9010 # BTX entry point
42 .set MEM_USR,0xa000 # Client start
43 .set BDA_BOOT,0x472 # Boot howto flag
46 .set SIZ_PAG,0x1000 # Page size
47 .set SIZ_SEC,0x200 # Sector size
53 * Copy BTX and boot2 to the right locations and start it all up.
57 * Setup the segment registers to flat addressing (segment 0) and setup the
58 * stack to end just below the start of our code.
60 start: xor %cx,%cx # Zero
64 mov $start,%sp # stack
67 * BTX is right after us at 'end'. We read the length of BTX out of
68 * its header to find boot2. We need to copy boot2 to MEM_USR and BTX
69 * to MEM_BTX. Since those might overlap, we have to copy boot2
70 * backwards first and then copy BTX. We aren't sure exactly how long
71 * boot2 is, but we assume it can't be longer than 64k, so we just always
75 mov 0xa(%bx),%si # Get BTX length and set
76 add %bx,%si # %si to start of boot2
77 mov %si,%ax # Align %ds:%si on a
78 shr $4,%ax # paragraph boundary
79 and $0xf,%si # with the smallest
80 mov %ax,%ds # possible %si
81 add $(64 * 1024 - 16),%si
82 mov $MEM_USR/16,%ax # Point %es:%di at end of
83 mov $(64 * 1024 - 16),%di # largest boot2 range
86 mov %di,%cx # Copy 64k - paragraph + 1
89 mov %cx,%ds # Reset %ds and %es
91 mov 0xa(%bx),%cx # Get BTX length and set
92 mov %bx,%si # %si to end of BTX
93 mov $MEM_BTX,%di # %di -> end of BTX at
101 * Enable A20 so we can access memory above 1 meg.
102 * Use the zero-valued %cx as a timeout for embedded hardware which do not
103 * have a keyboard controller.
105 seta20: cli # Disable interrupts
106 seta20.1: dec %cx # Timeout?
108 inb $0x64,%al # Get status
109 testb $0x2,%al # Busy?
111 movb $0xd1,%al # Command: Write
112 outb %al,$0x64 # output port
113 seta20.2: inb $0x64,%al # Get status
114 testb $0x2,%al # Busy?
116 movb $0xdf,%al # Enable
118 seta20.3: sti # Enable interrupts
121 * Save drive number from BIOS so boot2 can see it and start BTX.
124 jmp MEM_JMP # Start BTX