418 lines
12 KiB
ArmAsm
418 lines
12 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,0xc # Table 1 size
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.set MAGIC,0xaa55 # Magic: bootable
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.set B0MAGIC,0xbb66 # Identification
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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 immediately 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 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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incb -0xe(%di) # Sector number
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jmp main-LOAD+ORIGIN # To relocated code
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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: testb $0x20,_FLAGS(%bp) # Set number drive?
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jnz main.1 # Yes
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testb %dl,%dl # Drive number valid?
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js main.2 # Possibly (0x80 set)
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main.1: movb _SETDRV(%bp),%dl # Drive number to use
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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: movb %dl,_FAKE(%bp) # Save drive number
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callw 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 has 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: movb %ch,-0x4(%bx) # Zero active flag (ch == 0)
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btw %dx,_FLAGS(%bp) # Entry enabled?
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jnc main.5 # No
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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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movb (%bx),%al # Load type
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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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je main.5 # Yes
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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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jne main.4 # No
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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: movb (%di),%cl # Partition
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addw %cx,%di # description
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callw 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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jnc main.3 # Till done
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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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jb main.6 # Yes
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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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jz main.7 # Yes
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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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movb %al,_NXTDRV(%bp) # drive number
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movw $drive,%di # Display
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callw 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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callw putstr # prompt
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movb _OPT(%bp),%dl # Display
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decw %si # default
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callw 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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addw _TICKS(%bp),%di # timeout
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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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jnz main.11 # Have one
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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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jb main.8 # No
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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: movb _OPT(%bp),%al # Load default
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jmp main.12 # Join common code
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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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callw 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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je main.9 # Yes
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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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ja main.10 # No
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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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btw %ax,_MNUOPT(%bp) # enabled?
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jnc main.10 # No
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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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movb %al,_OPT(%bp) # Save option
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movw $FAKE,%si # Partition for write
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movb (%si),%dl # Drive number
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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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je main.13 # Yes
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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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movb $0x80,(%bx) # Flag active
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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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testb $0x40,_FLAGS(%bp) # No updates?
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jnz main.14 # Yes
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movw $start,%bx # Data to write
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movb $0x3,%ah # Write sector
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callw 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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jne main.15 # If not F5
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movb _NXTDRV(%bp),%dl # Next drive
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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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callw intx13 # from disk
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jc main.10 # If error
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cmpw $MAGIC,0x1fe(%bx) # Bootable?
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jne main.10 # No
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pushw %si # Save
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movw $crlf,%si # Leave some
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callw puts # space
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popw %si # Restore
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jmp *%bx # Invoke bootstrap
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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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callw putchr # 'F'
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movb $'1',%al # Prepare
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addb %dl,%al # digit
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jmp putstr.1 # Display the rest
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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: btsw %dx,_MNUOPT(%bp) # Enable menu option
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movw $item,%si # Display
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callw putkey # key
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movw %di,%si # Display the rest
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puts: callw 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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jnz putstr.2 # Yes
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putstr.1: callw putchr # Display char
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jmp putstr # Continue
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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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retw # To caller
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# One-sector disk I/O routine
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intx13: movb 0x1(%si),%dh # Load head
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movw 0x2(%si),%cx # Load cylinder:sector
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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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testb $0x80,_FLAGS(%bp) # Use packet interface?
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jz intx13.1 # No
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pushl $0x0 # Set the
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pushl 0x8(%si) # LBA address
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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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retw # 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 values indicate bootable 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 0x9f, 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_bsd-. # BSD/OS
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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-0xe,0x90
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.word B0MAGIC # Magic number
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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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