99 lines
2.7 KiB
ArmAsm
99 lines
2.7 KiB
ArmAsm
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# Copyright (c) 1999 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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# $Id: $
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# Master boot record
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.set LOAD,0x7c00 # Load address
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.set EXEC,0x600 # Execution address
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.set PT_OFF,0x1be # Partition table
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.set MAGIC,0xaa55 # Magic: bootable
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.set NDRIVE,0x8 # Drives to support
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.globl start # Entry point
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start: cld # String ops inc
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xorl %eax,%eax # Zero
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movl %eax,%es # Address
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movl %eax,%ds # data
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cli # Disable interrupts
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movl %eax,%ss # Set up
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movwir(LOAD,_sp) # stack
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sti # Enable interrupts
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movwir(main-EXEC+LOAD,_si) # Source
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movwir(main,_di) # Destination
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movwir(0x200-(main-start),_cx) # Word count
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rep # Relocate
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movsb # code
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jmpnwi(main-LOAD+EXEC) # To relocated code
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main: xorl %esi,%esi # No active found
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movwir(partbl,_bx) # Partition table
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movb $0x4,%cl # Entries
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main.1: cmpbr0(_ch,_bx_) # Null entry?
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je main.2 # Yes
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jg err_pt # If bit 7 unset
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testl %esi,%esi # Active found?
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jnz err_pt # Yes
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movl %ebx,%esi # Keep place
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main.2: addb $0x10,%bl # Till
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loop main.1 # done
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testl %esi,%esi # Active found?
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jnz main.3 # Yes
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int $0x18 # BIOS: Diskless boot
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main.3: cmpb $0x80,%dl # Drive valid?
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jb main.4 # No
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cmpb $0x80+NDRIVE,%dl # Within range?
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jb main.5 # Yes
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main.4: movb0r(_si_,_dl) # Load drive
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main.5: movb1r(0x1,_si_,_dh) # Load head
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movw1r(0x2,_si_,_cx) # Load cylinder:sector
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movwir(LOAD,_bx) # Transfer buffer
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movwir(0x201,_ax) # BIOS: Read from
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int $0x13 # disk
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jc err_rd # If error
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cmpwi2(MAGIC,0x1fe,_bx_) # Bootable?
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jne err_os # No
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jmp *%ebx # Invoke bootstrap
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err_pt: movwir(msg_pt,_si) # "Invalid partition
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jmp putstr # table"
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err_rd: movwir(msg_rd,_si) # "Error loading
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jmp putstr # operating system"
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err_os: movwir(msg_os,_si) # "Missing operating
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jmp putstr # system"
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putstr.0: movwir(0x7,_bx) # Page:attribute
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movb $0xe,%ah # BIOS: Display
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int $0x10 # character
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putstr: lodsb # Get character
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testb %al,%al # End of string?
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jnz putstr.0 # No
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putstr.1: jmp putstr.1 # Await reset
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msg_pt: .asciz "Invalid partition table"
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msg_rd: .asciz "Error loading operating system"
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msg_os: .asciz "Missing operating system"
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.org PT_OFF
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partbl: .fill 0x10,0x4,0x0 # Partition table
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.word MAGIC # Magic number
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