| 1 | #
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| 2 | # Copyright (C) 2001-2004 Jakub Jermar
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| 3 | # All rights reserved.
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| 4 | #
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| 5 | # Redistribution and use in source and binary forms, with or without
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| 6 | # modification, are permitted provided that the following conditions
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| 7 | # are met:
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| 8 | #
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| 9 | # - Redistributions of source code must retain the above copyright
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| 10 | # notice, this list of conditions and the following disclaimer.
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| 11 | # - Redistributions in binary form must reproduce the above copyright
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| 12 | # notice, this list of conditions and the following disclaimer in the
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| 13 | # documentation and/or other materials provided with the distribution.
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| 14 | # - The name of the author may not be used to endorse or promote products
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| 15 | # derived from this software without specific prior written permission.
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| 16 | #
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| 17 | # THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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| 18 | # IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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| 19 | # OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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| 20 | # IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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| 21 | # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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| 22 | # NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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| 23 | # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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| 24 | # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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| 25 | # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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| 26 | # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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| 27 | #
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| 28 |
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| 29 | # This is a very primitive boot.s
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| 30 |
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| 31 | # It assumes that the first sector of the kernel image is found
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| 32 | # on head 0, track 0, sector 2 of the first floppy drive (1440K).
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| 33 | # Next kernel sectors follow on disk sector 3, 4, ...
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| 34 | #
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| 35 |
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| 36 |
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| 37 | # KERNEL_SIZE is passed from the outside to the preprocessor
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| 38 | #if (KERNEL_SIZE%512>0)
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| 39 | #define TAIL 1
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| 40 | #else
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| 41 | #define TAIL 0
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| 42 | #endif
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| 43 |
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| 44 | #define SECTORS (KERNEL_SIZE/512+TAIL)
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| 45 |
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| 46 | .text
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| 47 | .global _start_0x7c00
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| 48 |
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| 49 | .code16
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| 50 | _start_0x7c00:
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| 51 | xorw %ax,%ax # reset, %al will be used below
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| 52 | movw %ax,%dx # fd0, %dh and %dl will be used below
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| 53 | movw %dx,%ds
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| 54 |
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| 55 | movw %dx,%ss # initialize stack
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| 56 | movw $stack,%sp
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| 57 |
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| 58 | int $0x13 # reset floppy
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| 59 | jc stop_trying
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| 60 |
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| 61 | movw %dx,%ds
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| 62 | movw %dx,%ss
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| 63 | movw $0x7c00,%sp
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| 64 | movw $0xffe0,%si # after next increment, %si will become 0x0000
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| 65 | movw %si,%es
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| 66 | movw $0x8000,%bx # at %es:%bx
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| 67 |
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| 68 | movl $(SECTORS),%edi
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| 69 |
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| 70 | read_next:
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| 71 | test %edi,%edi
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| 72 | jnz read_sectors
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| 73 |
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| 74 | movb $12,%al
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| 75 | movw $0x3f2,%dx
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| 76 | outb %al,%dx
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| 77 |
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| 78 | movb $('$'),%al
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| 79 | call echo_mark
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| 80 |
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| 81 | jmpl $0,$0x8000
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| 82 |
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| 83 | read_sectors:
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| 84 | movb $('.'),%al
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| 85 | call echo_mark
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| 86 |
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| 87 | decl %edi
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| 88 | incw logical_sector
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| 89 | movw %es,%si
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| 90 | addw $0x20,%si
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| 91 | movw %si,%es
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| 92 |
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| 93 | movw logical_sector,%ax
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| 94 | divb sectors
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| 95 |
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| 96 | movb %ah,%cl
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| 97 | incb %cl # sector
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| 98 |
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| 99 | movb %al,%ch
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| 100 | shrb $1,%ch # track
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| 101 |
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| 102 | movb %al,%dh
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| 103 | andb $1,%dh # head
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| 104 |
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| 105 | movw $0x0201,%ax
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| 106 | int $0x13
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| 107 | jnc read_next
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| 108 |
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| 109 | movb $('R'),%al
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| 110 | call echo_mark
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| 111 |
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| 112 | xorw %ax,%ax # try to reset
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| 113 | movw %ax,%dx # fd0
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| 114 | int $0x13
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| 115 | jnc read_next
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| 116 |
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| 117 | stop_trying:
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| 118 | movb $('F'),%al
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| 119 | call echo_mark
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| 120 |
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| 121 | cli
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| 122 | hlt
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| 123 |
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| 124 | CH=4
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| 125 | echo_mark:
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| 126 | push %bp
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| 127 | movw %sp,%bp
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| 128 | pusha
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| 129 |
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| 130 | movb $0xe,%ah
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| 131 | movb $7,%bl
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| 132 | int $0x10
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| 133 |
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| 134 | popa
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| 135 | pop %bp
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| 136 | ret
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| 137 |
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| 138 | # current logical sector from the beginning of the disk
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| 139 | logical_sector:
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| 140 | .word 0
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| 141 |
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| 142 | # number of sectors per track on 1440 floppy
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| 143 | sectors:
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| 144 | .byte 18
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| 145 |
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| 146 | # boot floppy signature
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| 147 | .org 0x1fe
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| 148 | boot_floppy_signature:
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| 149 | .byte 0x55
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| 150 | .byte 0xaa
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| 151 | stack:
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