| 1 | ! jumpboot 1.0 - Jump to another bootstrap Author: Kees J. Bot
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| 2 | ! 14 Apr 1999
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| 3 | !
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| 4 | ! This code may be placed into any free boot sector, like the first sector
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| 5 | ! of an extended partition, a file system partition other than the root,
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| 6 | ! or even the master bootstrap. It will load and run another bootstrap whose
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| 7 | ! disk, partition, and slice number (not necessarily all three) are patched
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| 8 | ! into this code by installboot. If the ALT key is held down when this code
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| 9 | ! is booted then you can type the disk, partition, and slice numbers manually.
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| 10 | ! The manual interface is default if no numbers are patched in by installboot.
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| 11 | !
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| 12 |
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| 13 | o32 = 0x66 ! This assembler doesn't know 386 extensions
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| 14 | LOADOFF = 0x7C00 ! 0x0000:LOADOFF is where this code is loaded
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| 15 | BUFFER = 0x0600 ! First free memory
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| 16 | PART_TABLE = 446 ! Location of partition table within master
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| 17 | PENTRYSIZE = 16 ! Size of one partition table entry
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| 18 | MAGIC = 510 ! Location of the AA55 magic number
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| 19 |
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| 20 | ! <ibm/partition.h>:
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| 21 | MINIX_PART = 0x81
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| 22 | sysind = 4
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| 23 | lowsec = 8
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| 24 |
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| 25 |
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| 26 | .text
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| 27 |
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| 28 | ! Find and load another bootstrap and jump to it.
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| 29 | jumpboot:
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| 30 | xor ax, ax
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| 31 | mov ds, ax
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| 32 | mov es, ax
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| 33 | cli
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| 34 | mov ss, ax ! ds = es = ss = Vector segment
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| 35 | mov sp, #LOADOFF
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| 36 | sti
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| 37 |
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| 38 | ! Move this code to safety, then jump to it.
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| 39 | mov si, sp ! si = start of this code
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| 40 | mov di, #BUFFER ! di = Buffer area
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| 41 | mov cx, #512/2 ! One sector
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| 42 | cld
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| 43 | rep movs
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| 44 | jmpf BUFFER+migrate, 0 ! To safety
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| 45 | migrate:
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| 46 |
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| 47 | mov bp, #BUFFER+guide ! Patched guiding characters
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| 48 | altkey:
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| 49 | movb ah, #0x02 ! Keyboard shift status
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| 50 | int 0x16
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| 51 | testb al, #0x08 ! Bit 3 = ALT key
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| 52 | jz noalt ! ALT key pressed?
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| 53 | again:
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| 54 | mov bp, #zero ! Ignore patched stuff
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| 55 | noalt:
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| 56 |
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| 57 | ! Follow guide characters to find the boot partition.
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| 58 | call print
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| 59 | .ascii "d?\b\0" ! Initial greeting
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| 60 |
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| 61 | ! Disk number?
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| 62 | disk:
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| 63 | movb dl, #0x80 - 0x30 ! Prepare to add an ASCII digit
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| 64 | call getch ! Get number to tell which disk
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| 65 | addb dl, al ! dl = 0x80 + (al - '0')
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| 66 | jns n0nboot ! Result should be >= 0x80
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| 67 | mov si, #BUFFER+zero-lowsec ! si = where lowsec(si) is zero
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| 68 | cmpb (bp), #0x23 ! Next guide character is '#'?
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| 69 | jne notlogical
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| 70 | lea si, 1-lowsec(bp) ! Logical sector offset follows '#'
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| 71 | notlogical:
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| 72 | call load ! Load chosen sector of chosen disk
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| 73 | cmpb (bp), #0x23
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| 74 | je boot ! Run bootstrap if a logical is chosen
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| 75 |
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| 76 | call print ! Intro to partition number
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| 77 | .ascii "p?\b\0"
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| 78 |
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| 79 | part:
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| 80 | call getch ! Get character to tell partition
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| 81 | call gettable ! Get partition table
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| 82 | call sort ! Sort partition table
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| 83 | call choose_load ! Compute chosen entry and load
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| 84 |
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| 85 | cmpb sysind(si), #MINIX_PART ! Minix subpartition table possible?
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| 86 | jne waitboot
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| 87 |
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| 88 | call print ! Intro to slice number
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| 89 | .ascii "s?\b\0"
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| 90 |
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| 91 | slice:
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| 92 | call getch ! Get character to tell slice
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| 93 | call gettable ! Get partition table
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| 94 | call choose_load ! Compute chosen entry and load
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| 95 |
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| 96 | waitboot:
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| 97 | call print ! Intro to nothing
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| 98 | .ascii " ?\b\0"
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| 99 | call getch ! Supposed to type RETURN now
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| 100 | n0nboot:jmp nonboot ! Sorry, can't go further
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| 101 |
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| 102 | ! Get a character, either the patched-in, or one from the keyboard.
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| 103 | getch:
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| 104 | movb al, (bp) ! Get patched-in character
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| 105 | testb al, al
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| 106 | jz getkey
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| 107 | inc bp
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| 108 | jmp gotkey
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| 109 | getkey: xorb ah, ah ! Wait for keypress
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| 110 | int 0x16
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| 111 | gotkey: testb dl, dl ! Ignore CR if disk number not yet set
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| 112 | jns putch
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| 113 | cmpb al, #0x0D ! Carriage return?
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| 114 | je boot
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| 115 | !jmp putch
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| 116 |
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| 117 | ! Print a character
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| 118 | putch: movb ah, #0x0E ! Print character in teletype mode
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| 119 | mov bx, #0x0001 ! Page 0, foreground color
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| 120 | int 0x10
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| 121 | ret
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| 122 |
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| 123 | ! Print a message.
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| 124 | print: mov cx, si ! Save si
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| 125 | pop si ! si = String following 'call print'
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| 126 | prnext: lodsb ! al = *si++ is char to be printed
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| 127 | testb al, al ! Null marks end
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| 128 | jz prdone
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| 129 | call putch
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| 130 | jmp prnext
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| 131 | prdone: xchg si, cx ! Restore si
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| 132 | jmp (cx) ! Continue after the string
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| 133 |
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| 134 | ! Return typed (or in patched data) means to run the bootstrap now in core!
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| 135 | boot:
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| 136 | call print ! Make line on screen look proper
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| 137 | .ascii "\b \r\n\0"
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| 138 | jmp LOADOFF-BUFFER ! Jump to LOADOFF
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| 139 |
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| 140 | ! Compute address of chosen partition entry from choice al into si, then
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| 141 | ! continue to load the boot sector of that partition.
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| 142 | choose_load:
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| 143 | subb al, #0x30 ! al -= '0'
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| 144 | cmpb al, #4 ! Only four partitions
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| 145 | ja n0nboot
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| 146 | movb ah, #PENTRYSIZE
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| 147 | mulb ah ! al *= PENTRYSIZE
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| 148 | add ax, #BUFFER+PART_TABLE
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| 149 | mov si, ax ! si = &part_table[al - '0']
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| 150 | movb al, sysind(si) ! System indicator
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| 151 | testb al, al ! Unused partition?
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| 152 | jz n0nboot
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| 153 | !jmp load ! Continue to load boot sector
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| 154 |
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| 155 | ! Load boot sector of the current partition.
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| 156 | load:
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| 157 | push dx ! Save drive code
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| 158 | push es ! Next call sets es
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| 159 | movb ah, #0x08 ! Code for drive parameters
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| 160 | int 0x13
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| 161 | pop es
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| 162 | andb cl, #0x3F ! cl = max sector number (1-origin)
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| 163 | incb dh ! dh = 1 + max head number (0-origin)
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| 164 | movb al, cl ! al = cl = sectors per track
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| 165 | mulb dh ! dh = heads, ax = heads * sectors
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| 166 | mov bx, ax ! bx = sectors per cylinder = heads * sectors
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| 167 | mov ax, lowsec+0(si)
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| 168 | mov dx, lowsec+2(si) ! dx:ax = sector within drive
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| 169 | cmp dx, #[1024*255*63-255]>>16 ! Near 8G limit?
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| 170 | jae bigdisk
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| 171 | div bx ! ax = cylinder, dx = sector within cylinder
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| 172 | xchg ax, dx ! ax = sector within cylinder, dx = cylinder
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| 173 | movb ch, dl ! ch = low 8 bits of cylinder
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| 174 | divb cl ! al = head, ah = sector (0-origin)
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| 175 | xorb dl, dl ! About to shift bits 8-9 of cylinder into dl
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| 176 | shr dx, #1
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| 177 | shr dx, #1 ! dl[6..7] = high cylinder
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| 178 | orb dl, ah ! dl[0..5] = sector (0-origin)
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| 179 | movb cl, dl ! cl[0..5] = sector, cl[6..7] = high cyl
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| 180 | incb cl ! cl[0..5] = sector (1-origin)
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| 181 | pop dx ! Restore drive code in dl
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| 182 | movb dh, al ! dh = al = head
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| 183 | mov bx, #LOADOFF ! es:bx = where sector is loaded
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| 184 | mov ax, #0x0201 ! ah = Code for read / al = one sector
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| 185 | int 0x13
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| 186 | jmp rdeval ! Evaluate read result
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| 187 | bigdisk:
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| 188 | mov bx, dx ! bx:ax = dx:ax = sector to read
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| 189 | pop dx ! Restore drive code in dl
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| 190 | push si ! Save si
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| 191 | mov si, #BUFFER+ext_rw ! si = extended read/write parameter packet
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| 192 | mov 8(si), ax ! Starting block number = bx:ax
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| 193 | mov 10(si), bx
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| 194 | movb ah, #0x42 ! Extended read
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| 195 | int 0x13
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| 196 | pop si ! Restore si to point to partition entry
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| 197 | !jmp rdeval
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| 198 | rdeval:
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| 199 | jnc rdok
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| 200 | rderr:
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| 201 | call print
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| 202 | .ascii "\r\nRead error\r\n\0"
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| 203 | jmp again
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| 204 | rdok:
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| 205 | cmp LOADOFF+MAGIC, #0xAA55
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| 206 | je sigok ! Signature ok?
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| 207 | nonboot:
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| 208 | call print
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| 209 | .ascii "\r\nNot bootable\r\n\0"
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| 210 | jmp again
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| 211 | sigok:
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| 212 | ret
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| 213 |
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| 214 | ! Get the partition table into my space.
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| 215 | gettable:
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| 216 | mov si, #LOADOFF+PART_TABLE
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| 217 | mov di, #BUFFER+PART_TABLE
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| 218 | mov cx, #4*PENTRYSIZE/2
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| 219 | rep movs
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| 220 | ret
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| 221 |
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| 222 | ! Sort the partition table.
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| 223 | sort:
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| 224 | mov cx, #4 ! Four times is enough to sort
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| 225 | bubble: mov si, #BUFFER+PART_TABLE ! First table entry
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| 226 | bubble1:lea di, PENTRYSIZE(si) ! Next entry
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| 227 | cmpb sysind(si), ch ! Partition type, nonzero when in use
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| 228 | jz exchg ! Unused entries sort to the end
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| 229 | inuse: mov bx, lowsec+0(di)
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| 230 | sub bx, lowsec+0(si) ! Compute di->lowsec - si->lowsec
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| 231 | mov bx, lowsec+2(di)
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| 232 | sbb bx, lowsec+2(si)
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| 233 | jae order ! In order if si->lowsec <= di->lowsec
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| 234 | exchg: movb bl, (si)
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| 235 | xchgb bl, PENTRYSIZE(si) ! Exchange entries byte by byte
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| 236 | movb (si), bl
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| 237 | inc si
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| 238 | cmp si, di
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| 239 | jb exchg
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| 240 | order: mov si, di
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| 241 | cmp si, #BUFFER+PART_TABLE+3*PENTRYSIZE
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| 242 | jb bubble1
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| 243 | loop bubble
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| 244 | ret
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| 245 |
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| 246 | .data
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| 247 |
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| 248 | ! Extended read/write commands require a parameter packet.
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| 249 | ext_rw:
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| 250 | .data1 0x10 ! Length of extended r/w packet
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| 251 | .data1 0 ! Reserved
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| 252 | .data2 1 ! Blocks to transfer (just one)
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| 253 | .data2 LOADOFF ! Buffer address offset
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| 254 | .data2 0 ! Buffer address segment
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| 255 | .data4 0 ! Starting block number low 32 bits (tbfi)
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| 256 | zero: .data4 0 ! Starting block number high 32 bits
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| 257 |
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| 258 | .align 2
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| 259 | guide:
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| 260 | ! Guide characters and possibly a logical partition number patched here by
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| 261 | ! installboot, up to 6 bytes maximum.
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