773065b3b8
code instead of using 32-bit code and having to just "know" that it's really 16-bit instructions when things run. This also allows the code to use fewer macros and more actual assembly statements, which eases maintenance. Unfortunately, due to as(1) brokenness, we still use m4 macros for all 16-bit addresses, and all short jumps (i.e., 8-bit relative addresses in the jump instruction) must be wrapped in .code32 directives to avoid useless bloat by as(1). This also fixes a few problems that were preventing boot0 from compiling with the latest and greatest version of as(1).
488 lines
13 KiB
ArmAsm
488 lines
13 KiB
ArmAsm
#
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# Copyright (c) 1998 Robert Nordier
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms are freely
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# permitted provided that the above copyright notice and this
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# paragraph and the following disclaimer are duplicated in all
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# such forms.
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#
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# This software is provided "AS IS" and without any express or
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# implied warranties, including, without limitation, the implied
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# warranties of merchantability and fitness for a particular
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# purpose.
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#
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# $FreeBSD$
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# A 512-byte boot manager.
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.set NHRDRV,0x475 # Number of hard drives
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.set ORIGIN,0x600 # Execution address
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.set FAKE,0x800 # Partition entry
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.set LOAD,0x7c00 # Load address
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.set PRT_OFF,0x1be # Partition table
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.set TBL0SZ,0x3 # Table 0 size
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.set TBL1SZ,0xb # Table 1 size
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.set MAGIC,0xaa55 # Magic: bootable
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.set KEY_ENTER,0x1c # Enter key scan code
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.set KEY_F1,0x3b # F1 key scan code
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#
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# Addresses in the sector of embedded data values.
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# Accessed with negative offsets from the end of the relocated sector (%ebp).
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#
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.set _NXTDRV,-0x48 # Next drive
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.set _OPT,-0x47 # Default option
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.set _SETDRV,-0x46 # Drive to force
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.set _FLAGS,-0x45 # Flags
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.set _TICKS,-0x44 # Timeout ticks
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.set _FAKE,0x0 # Fake partition entry
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.set _MNUOPT,0xc # Menu options
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.globl start # Entry point
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.code16 # This runs in real mode
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#
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# Initialise segments and registers to known values.
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# segments start at 0.
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# The stack is immediatly below the address we were loaded to.
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#
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start: cld # String ops inc
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xorw %ax,%ax # Zero
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movw %ax,%es # Address
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movw %ax,%ds # data
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movw %ax,%ss # Set up
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movw $LOAD,%sp # stack
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#
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# Copy this code to the address it was linked for
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#
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movw %sp,%si # Source
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movw $start,%di # Destination
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movw $0x100,%cx # Word count
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rep # Relocate
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movsw # code
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#
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# Set address for variable space beyond code, and clear it.
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# Notice that this is also used to point to the values embedded in in the block,
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# by using negative offsets.
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#
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movw %di,%bp # Address variables
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movb $0x8,%cl # Words to clear
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rep # Zero
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stosw # them
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#
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# Relocate to the new copy of the code.
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#
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incb1(-0xe,_di_) # Sector number
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/* incb $-0xe(%di) */
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jmpnwi(main-LOAD+ORIGIN) # To relocated code
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/* jmp main-LOAD+ORIGIN */
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#
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# Check what flags were loaded with us, specifically, Use a predefined Drive.
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# If what the bios gives us is bad, use the '0' in the block instead, as well.
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#
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main: tstbi1(0x20,_FLAGS,_bp_) # Set number drive?
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/* testb $(0x20+_FLAGS)(%bp) */
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.code32
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jnz main.1 # Yes
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.code16
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testb %dl,%dl # Drive number valid?
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.code32
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js main.2 # Possibly (0x80 set)
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.code16
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main.1: movb1r(_SETDRV,_bp_,_dl) # Drive number to use
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/* movb $_SETDRV(%bp),%dl */
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#
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# Whatever we decided to use, now store it into the fake
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# partition entry that lives in the data space above us.
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#
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main.2: movbr1(_dl,_FAKE,_bp_) # Save drive number
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/* movb %dl,$_FAKE(%bp) */
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callwi(putn) # To new line
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pushw %dx # Save drive number
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#
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# Start out with a pointer to the 4th byte of the first table entry
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# so that after 4 iterations it's beyond the end of the sector.
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# and beyond a 256 byte boundary and thos overflowed 8 bits (see next comment).
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# (remember that the table starts 2 bytes earlier than you would expect
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# as the bootable flag is after it in the block)
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#
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movw $(partbl+0x4),%bx # Partition table (+4)
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xorw %dx,%dx # Item number
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#
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# Loop around on the partition table, printing values until we
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# pass a 256 byte boundary. The end of loop test is at main.5.
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#
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main.3: movbr1(_ch,-0x4,_bx_) # Zero active flag (ch == 0)
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/* movb %ch,$-0x4(%bx) */
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btwr1(_dx,_FLAGS,_bp_) # Entry enabled?
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/* bt %dx,$_FLAGS(%bp) */
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.code32
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jnc main.5 # No
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.code16
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#
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# If any of the entries in the table are
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# the same as the 'type' in the slice table entry,
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# then this is an empty or non bootable partition. Skip it.
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#
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movb0r(_bx_,_al) # Load type
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/* movb (%bx),%al */
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movw $tables,%di # Lookup tables
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movb $TBL0SZ,%cl # Number of entries
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repne # Exclude
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scasb # partition?
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.code32
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je main.5 # Yes
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.code16
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#
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# Now scan the table of known types
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#
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movb $TBL1SZ,%cl # Number of entries
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repne # Known
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scasb # type?
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.code32
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jne main.4 # No
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.code16
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#
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# If it matches get the matching element in the
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# next array. if it doesn't, we are already
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# pointing at its first element which points to a "?".
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#
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addw $TBL1SZ,%di # Adjust
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main.4: movb0r(_di_,_cl) # Partition
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/* movb (%di),%cl */
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addw %cx,%di # description
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callwi(putx) # Display it
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main.5: incw %dx # Next item
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addb $0x10,%bl # Next entry
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.code32
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jnc main.3 # Till done
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.code16
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#
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# Passed a 256 byte boundary..
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# table is finished.
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# Add one to the drive number and check it is valid,
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#
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popw %ax # Drive number
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subb $0x80-0x1,%al # Does next
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cmpb NHRDRV,%al # drive exist? (from BIOS?)
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.code32
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jb main.6 # Yes
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.code16
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# If not then if there is only one drive,
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# Don't display drive as an option.
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#
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decw %ax # Already drive 0?
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.code32
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jz main.7 # Yes
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.code16
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# If it was illegal or we cycled through them,
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# then go back to drive 0.
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#
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xorb %al,%al # Drive 0
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#
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# Whatever drive we selected, make it an ascii digit and save it back
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# to the "next drive" location in the loaded block in case we
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# want to save it for next time.
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# This also is part of the printed drive string so add 0x80 to indicate
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# end of string.
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#
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main.6: addb $'0'|0x80,%al # Save next
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movbr1(_al,_NXTDRV,_bp_) # drive number
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/* movb %al,$NXTDRV(%bp) */
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movw $drive,%di # Display
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callwi(putx) # item
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#
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# Now that we've printed the drive (if we needed to), display a prompt.
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# Get ready for the input byt noting the time.
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#
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main.7: movw $prompt,%si # Display
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callwi(putstr) # prompt
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movb1r(_OPT,_bp_,_dl) # Display
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/* movb $_OPT(%bp),%dl */
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decw %si # default
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callwi(putkey) # key
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xorb %ah,%ah # BIOS: Get
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int $0x1a # system time
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movw %dx,%di # Ticks when
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addw1r(_TICKS,_bp_,_di) # timeout
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/* addw $_TICKS(%bp),%di */
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#
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# Busy loop, looking for keystrokes but
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# keeping one eye on the time.
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#
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main.8: movb $0x1,%ah # BIOS: Check
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int $0x16 # for keypress
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.code32
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jnz main.11 # Have one
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.code16
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xorb %ah,%ah # BIOS: Get
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int $0x1a # system time
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cmpw %di,%dx # Timeout?
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.code32
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jb main.8 # No
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.code16
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#
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# If timed out or defaulting, come here.
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#
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main.9: movb1r(_OPT,_bp_,_al) # Load default
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/* movb $_OPT(%bp),%al */
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.code32
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jmp main.12 # Join common code
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.code16
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#
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# User's last try was bad, beep in displeasure.
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# Since nothing was printed, just continue on as if the user
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# hadn't done anything. This gives the effect of the user getting a beep
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# for all bad keystrokes but no action until either the timeout
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# occurs or the user hits a good key.
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#
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main.10: movb $0x7,%al # Signal
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callwi(putchr) # error
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#
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# Get the keystroke.
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#
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main.11: xorb %ah,%ah # BIOS: Get
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int $0x16 # keypress
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movb %ah,%al # Scan code
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#
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# If it's CR act as if timed out.
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#
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cmpb $KEY_ENTER,%al # Enter pressed?
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.code32
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je main.9 # Yes
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.code16
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#
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# Otherwise check if legal
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# If not ask again.
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#
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subb $KEY_F1,%al # Less F1 scan code
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cmpb $0x4,%al # F1..F5?
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.code32
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ja main.10 # No
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.code16
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#
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# We have a selection.
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# but if it's a bad selection go back to complain.
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# The bits in MNUOPT were set when the options were printed.
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# Anything not printed is not an option.
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#
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main.12: cbtw # Option
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btwr1(_ax,_MNUOPT,_bp_) # enabled?
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/* btw %ax,$_MNUOPT(%bp) */
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.code32
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jnc main.10 # No
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.code16
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#
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# Save the info in the original tables
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# for rewriting to the disk.
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#
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movbr1(_al,_OPT,_bp_) # Save option
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/* movb %al,$OPT(%bp) */
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movw $FAKE,%si # Partition for write
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movb0r(_si_,_dl) # Drive number
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/* movb (%si),%dl */
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movw %si,%bx # Partition for read
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cmpb $0x4,%al # F5 pressed?
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pushf # Save
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.code32
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je main.13 # Yes
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.code16
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shlb $0x4,%al # Point to
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addw $partbl,%ax # selected
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xchgw %bx,%ax # partition
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movbi0(0x80,_bx_) # Flag active
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/* movb $0x80,(%bx) */
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#
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# If not asked to do a write-back (flags 0x40) don't do one.
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#
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main.13: pushw %bx # Save
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tstbi1(0x40,_FLAGS,_bp_) # No updates?
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/* testb $0x40,$_FLAGS(%bp) */
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.code32
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jnz main.14 # Yes
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.code16
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movw $start,%bx # Data to write
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movb $0x3,%ah # Write sector
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callwi(intx13) # to disk
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main.14: popw %si # Restore
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popf # Restore
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#
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# If going to next drive, replace drive with selected one.
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# Remember to un-ascii it. Hey 0x80 is already set, cool!
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#
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.code32
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jne main.15 # If not F5
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.code16
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movb1r(_NXTDRV,_bp_,_dl) # Next drive
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/* movb $_NXTDRV(%bp),%dl */
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subb $'0',%dl # number
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#
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# load selected bootsector to the LOAD location in RAM.
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# If it fails to read or isn't marked bootable, treat it
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# as a bad selection.
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# XXX what does %si carry?
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#
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main.15: movw $LOAD,%bx # Address for read
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movb $0x2,%ah # Read sector
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callwi(intx13) # from disk
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.code32
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jc main.10 # If error
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.code16
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cmpwi2(MAGIC,0x1fe,_bx_) # Bootable?
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/* cmpw $MAGIC,$0x1fe(%bx) */
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.code32
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jne main.10 # No
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.code16
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pushw %si # Save
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movw $crlf,%si # Leave some
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callwi(puts) # space
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popw %si # Restore
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.code32
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jmp *%ebx # Invoke bootstrap
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/* jmp *%bx */
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.code16
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#
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# Display routines
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#
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putkey: movb $'F',%al # Display
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callwi(putchr) # 'F'
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movb $'1',%al # Prepare
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addb %dl,%al # digit
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.code32
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jmp putstr.1 # Display the rest
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.code16
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#
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# Display the option and note that it is a valid option.
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# That last point is a bit tricky..
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#
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putx: btswr1(_dx,_MNUOPT,_bp_) # Enable menu option
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/* btsw %dx,$_MNUOPT(%bp) */
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movw $item,%si # Display
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callwi(putkey) # key
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movw %di,%si # Display the rest
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puts: callwi(putstr) # Display string
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putn: movw $crlf,%si # To next line
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putstr: lodsb # Get byte
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testb $0x80,%al # End of string?
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.code32
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jnz putstr.2 # Yes
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.code16
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putstr.1: callwi(putchr) # Display char
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.code32
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jmp putstr # Continue
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.code16
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putstr.2: andb $~0x80,%al # Clear MSB
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putchr: pushw %bx # Save
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movw $0x7,%bx # Page:attribute
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movb $0xe,%ah # BIOS: Display
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int $0x10 # character
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popw %bx # Restore
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retn # To caller
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# One-sector disk I/O routine
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intx13: movb1r(0x1,_si_,_dh) # Load head
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/* movb $0x1(%si),%dh */
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movw1r(0x2,_si_,_cx) # Load cylinder:sector
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/* movw $0x2(%si),%cx */
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movb $0x1,%al # Sector count
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pushw %si # Save
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movw %sp,%di # Save
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tstbi1(0x80,_FLAGS,_bp_) # Use packet interface?
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/* testb $0x80,$_FLAGS(%bp) */
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.code32
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jz intx13.1 # No
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.code16
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pushl $0x0 # Set the
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o16 # LBA
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pushw1(0x8,_si_) # address
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/* pushl $0x8(%si) */
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pushw %es # Set the transfer
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pushw %bx # buffer address
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push $0x1 # Block count
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push $0x10 # Packet size
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movw %sp,%si # Packet pointer
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decw %ax # Verify off
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orb $0x40,%ah # Use disk packet
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intx13.1: int $0x13 # BIOS: Disk I/O
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movw %di,%sp # Restore
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popw %si # Restore
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retn # To caller
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# Menu strings
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item: .ascii " "; .byte ' '|0x80
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prompt: .ascii "\nDefault:"; .byte ' '|0x80
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crlf: .ascii "\r"; .byte '\n'|0x80
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# Partition type tables
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tables:
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#
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# These entries identify invalid or NON BOOT types and partitions.
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#
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.byte 0x0, 0x5, 0xf
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#
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# These valuse indicate botable types we know the names of
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#
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.byte 0x1, 0x4, 0x6, 0xb, 0xc, 0xe, 0x63, 0x83
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.byte 0xa5, 0xa6, 0xa9
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#
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# These are offsets that match the known names above and point to the strings
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# that will be printed.
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#
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.byte os_misc-. # Unknown
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.byte os_dos-. # DOS
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.byte os_dos-. # DOS
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.byte os_dos-. # DOS
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.byte os_dos-. # Windows
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.byte os_dos-. # Windows
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.byte os_dos-. # Windows
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.byte os_unix-. # UNIX
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.byte os_linux-. # Linux
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.byte os_freebsd-. # FreeBSD
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.byte os_bsd-. # OpenBSD
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.byte os_bsd-. # NetBSD
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#
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# And here are the strings themselves. 0x80 or'd into a byte indicates
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# the end of the string. (not so great for Russians but...)
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#
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os_misc: .ascii "?"; .byte '?'|0x80
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os_dos: .ascii "DO"; .byte 'S'|0x80
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os_unix: .ascii "UNI"; .byte 'X'|0x80
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os_linux: .ascii "Linu"; .byte 'x'|0x80
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os_freebsd: .ascii "Free"
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os_bsd: .ascii "BS"; .byte 'D'|0x80
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.org PRT_OFF-0xc,0x90
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#
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# These values are sometimes changed before writing back to the drive
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# Be especially careful that nxtdrv: must come after drive:, as it
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# is part of the same string.
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#
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drive: .ascii "Drive "
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nxtdrv: .byte 0x0 # Next drive number
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opt: .byte 0x0 # Option
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setdrv: .byte 0x80 # Drive to force
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flags: .byte FLAGS # Flags
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ticks: .word TICKS # Delay
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#
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# here is the 64 byte partition table that fdisk would fiddle with.
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#
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partbl: .fill 0x40,0x1,0x0 # Partition table
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.word MAGIC # Magic number
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