1/*- 2 * Copyright (c) 2007 Yahoo!, Inc. 3 * All rights reserved. 4 * Written by: John Baldwin <jhb@FreeBSD.org> 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 * 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. 17 * 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 28 * SUCH DAMAGE. 29 * 30 * $FreeBSD$ 31 * 32 * Partly from: src/sys/boot/i386/boot2/boot1.S 1.31 33 */ 34 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 44 45/* Misc. Constants */ 46 .set SIZ_PAG,0x1000 # Page size 47 .set SIZ_SEC,0x200 # Sector size 48 .set COPY_BLKS,0x8 # Number of blocks 49 # to copy for boot2 (<= 15) 50 .set COPY_BLK_SZ,0x8000 # Copy in 32k blocks; must be 51 # a multiple of 16 bytes 52 53 .globl start 54 .code16 55 56/* 57 * Copy BTX and boot2 to the right locations and start it all up. 58 */ 59 60/* 61 * Setup the segment registers to flat addressing (segment 0) and setup the 62 * stack to end just below the start of our code. 63 */ 64start: xor %cx,%cx # Zero 65 mov %cx,%es # Address 66 mov %cx,%ds # data 67 mov %cx,%ss # Set up 68 mov $start,%sp # stack 69 70/* 71 * BTX is right after us at 'end'. We read the length of BTX out of 72 * its header to find boot2. We need to copy boot2 to MEM_USR and BTX 73 * to MEM_BTX. Since those might overlap, we have to copy boot2 74 * backwards first and then copy BTX. We aren't sure exactly how long 75 * boot2 is, but it's currently under 256kB so we'll copy 8 blocks of 32kB 76 * each; this can be adjusted via COPY_BLK and COPY_BLK_SZ above. 77 */ 78 mov $end,%bx # BTX 79 mov 0xa(%bx),%si # Get BTX length and set 80 add %bx,%si # %si to start of boot2 81 dec %si # Set %ds:%si to point at the 82 mov %si,%ax # last byte we want to copy 83 shr $4,%ax # from boot2, with %si made as 84 add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # small as possible. 85 and $0xf,%si # 86 mov %ax,%ds # 87 mov $MEM_USR/16,%ax # Set %es:(-1) to point at 88 add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # the last byte we 89 mov %ax,%es # want to copy boot2 into. 90 mov $COPY_BLKS,%bx # Copy COPY_BLKS 32k blocks 91copyloop: 92 add $COPY_BLK_SZ,%si # Adjust %ds:%si to point at 93 mov %ds,%ax # the end of the next 32k to 94 sub $COPY_BLK_SZ/16,%ax # copy from boot2 95 mov %ax,%ds 96 mov $COPY_BLK_SZ-1,%di # Adjust %es:%di to point at 97 mov %es,%ax # the end of the next 32k into 98 sub $COPY_BLK_SZ/16,%ax # which we want boot2 copied 99 mov %ax,%es 100 mov $COPY_BLK_SZ,%cx # Copy 32k 101 std 102 rep movsb 103 dec %bx 104 jnz copyloop 105 mov %cx,%ds # Reset %ds and %es 106 mov %cx,%es 107 mov $end,%bx # BTX 108 mov 0xa(%bx),%cx # Get BTX length and set 109 mov %bx,%si # %si to end of BTX 110 mov $MEM_BTX,%di # %di -> end of BTX at 111 add %cx,%si # MEM_BTX 112 add %cx,%di 113 dec %si 114 dec %di 115 rep movsb # Move BTX 116 cld # String ops inc 117/* 118 * Enable A20 so we can access memory above 1 meg. 119 * Use the zero-valued %cx as a timeout for embedded hardware which do not 120 * have a keyboard controller. 121 */ 122seta20: cli # Disable interrupts 123seta20.1: dec %cx # Timeout? 124 jz seta20.3 # Yes 125 inb $0x64,%al # Get status 126 testb $0x2,%al # Busy? 127 jnz seta20.1 # Yes 128 movb $0xd1,%al # Command: Write 129 outb %al,$0x64 # output port 130seta20.2: inb $0x64,%al # Get status 131 testb $0x2,%al # Busy? 132 jnz seta20.2 # Yes 133 movb $0xdf,%al # Enable 134 outb %al,$0x60 # A20 135seta20.3: sti # Enable interrupts 136 137/* 138 * Save drive number from BIOS so boot2 can see it and start BTX. 139 */ 140 movb %dl,MEM_ARG 141 jmp start+MEM_JMP-MEM_ORG # Start BTX 142end: 143