# # Copyright (c) 1998 Robert Nordier # All rights reserved. # # Redistribution and use in source and binary forms are freely # permitted provided that the above copyright notice and this # paragraph and the following disclaimer are duplicated in all # such forms. # # This software is provided "AS IS" and without any express or # implied warranties, including, without limitation, the implied # warranties of merchantability and fitness for a particular # purpose. # # $FreeBSD$ .set MEM_REL,0x700 # Relocation address .set MEM_ARG,0x900 # Arguments .set MEM_ORG,0x7c00 # Origin .set MEM_BUF,0x8c00 # Load area .set MEM_BTX,0x9000 # BTX start .set MEM_JMP,0x9010 # BTX entry point .set MEM_USR,0xa000 # Client start .set PRT_OFF,0x1be # Partition offset .set PRT_NUM,0x4 # Partitions .set PRT_BSD,0xa5 # Partition type .set SIZ_PAG,0x1000 # Page size .set SIZ_SEC,0x200 # Sector size .globl start .globl xread .code16 start: jmp main # Start recognizably .org 0x4,0x90 # External read from disk xread: push %ss # Address pop %ds # data xread.1: # Starting pushl $0x0 # absolute push %cx # block push %ax # number push %es # Address of push %bx # transfer buffer xor %ax,%ax # Number of movb %dh,%al # blocks to push %ax # transfer push $0x10 # Size of packet mov %sp,%bp # Packet pointer callw read # Read from disk lea 0x10(%bp),%sp # Clear stack lret # To far caller # Bootstrap main: cld # String ops inc xor %cx,%cx # Zero mov %cx,%es # Address mov %cx,%ds # data mov %cx,%ss # Set up mov $start,%sp # stack mov %sp,%si # Source mov $MEM_REL,%di # Destination incb %ch # Word count rep # Copy movsw # code mov $part4,%si # Partition cmpb $0x80,%dl # Hard drive? jb main.4 # No movb $0x1,%dh # Block count callw nread # Read MBR mov $0x1,%cx # Two passes main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table movb $0x1,%dh # Partition main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type? jne main.3 # No jcxz main.5 # If second pass testb $0x80,(%si) # Active? jnz main.5 # Yes main.3: add $0x10,%si # Next entry incb %dh # Partition cmpb $0x1+PRT_NUM,%dh # In table? jb main.2 # Yes dec %cx # Do two jcxz main.1 # passes mov $msg_part,%si # Message jmp error # Error main.4: xor %dx,%dx # Partition:drive main.5: mov %dx,MEM_ARG # Save args movb $0x10,%dh # Sector count callw nread # Read disk mov $MEM_BTX,%bx # BTX mov 0xa(%bx),%si # Point past add %bx,%si # it mov $MEM_USR+SIZ_PAG,%di # Client page 1 mov $MEM_BTX+0xe*SIZ_SEC,%cx # Byte sub %si,%cx # count rep # Relocate movsb # client sub %di,%cx # Byte count xorb %al,%al # Zero rep # assumed stosb # bss callw seta20 # Enable A20 jmp start+MEM_JMP-MEM_ORG # Start BTX # Enable A20 seta20: cli # Disable interrupts seta20.1: inb $0x64,%al # Get status testb $0x2,%al # Busy? jnz seta20.1 # Yes movb $0xd1,%al # Command: Write outb %al,$0x64 # output port seta20.2: inb $0x64,%al # Get status testb $0x2,%al # Busy? jnz seta20.2 # Yes movb $0xdf,%al # Enable outb %al,$0x60 # A20 sti # Enable interrupts retw # To caller # Local read from disk nread: mov $MEM_BUF,%bx # Transfer buffer mov 0x8(%si),%ax # Get mov 0xa(%si),%cx # LBA push %cs # Read from callw xread.1 # disk jnc return # If success mov $msg_read,%si # Message # Error exit error: callw putstr # Display message mov $prompt,%si # Display callw putstr # prompt xorb %ah,%ah # BIOS: Get int $0x16 # keypress int $0x19 # BIOS: Reboot # Display string putstr.0: mov $0x7,%bx # Page:attribute movb $0xe,%ah # BIOS: Display int $0x10 # character putstr: lodsb # Get char testb %al,%al # End of string? jne putstr.0 # No ereturn: movb $0x1,%ah # Invalid stc # argument return: retw # To caller # Read from disk read: testb $0x80,%cs:MEM_REL+flags-start # LBA support enabled? jz read.1 # No mov $0x55aa,%bx # Magic push %dx # Save movb $0x41,%ah # BIOS: Check int $0x13 # extensions present pop %dx # Restore jc read.1 # If error cmp $0xaa55,%bx # Magic? jne read.1 # No testb $0x1,%cl # Packet interface? jz read.1 # No mov %bp,%si # Disk packet movb $0x42,%ah # BIOS: Extended int $0x13 # read retw # To caller read.1: push %dx # Save movb $0x8,%ah # BIOS: Get drive int $0x13 # parameters movb %dh,%ch # Max head number pop %dx # Restore jc return # If error andb $0x3f,%cl # Sectors per track jz ereturn # If zero cli # Disable interrupts mov 0x8(%bp),%eax # Get LBA push %dx # Save movzbl %cl,%ebx # Divide by xor %edx,%edx # sectors div %ebx # per track movb %ch,%bl # Max head number movb %dl,%ch # Sector number inc %bx # Divide by xorb %dl,%dl # number div %ebx # of heads movb %dl,%bh # Head number pop %dx # Restore cmpl $0x3ff,%eax # Cylinder number supportable? sti # Enable interrupts ja ereturn # No xchgb %al,%ah # Set up cylinder rorb $0x2,%al # number orb %ch,%al # Merge inc %ax # sector xchg %ax,%cx # number movb %bh,%dh # Head number subb %ah,%al # Sectors this track mov 0x2(%bp),%ah # Blocks to read cmpb %ah,%al # To read jb read.2 # this movb %ah,%al # track read.2: mov $0x5,%di # Try count read.3: les 0x4(%bp),%bx # Transfer buffer push %ax # Save movb $0x2,%ah # BIOS: Read int $0x13 # from disk pop %bx # Restore jnc read.4 # If success dec %di # Retry? jz read.6 # No xorb %ah,%ah # BIOS: Reset int $0x13 # disk system xchg %bx,%ax # Block count jmp read.3 # Continue read.4: movzbw %bl,%ax # Sectors read add %ax,0x8(%bp) # Adjust jnc read.5 # LBA, incw 0xa(%bp) # transfer read.5: shlb %bl # buffer add %bl,0x5(%bp) # pointer, sub %al,0x2(%bp) # block count ja read.1 # If not done read.6: retw # To caller # Messages msg_read: .asciz "Read" msg_part: .asciz "Boot" prompt: .asciz " error\r\n" flags: .byte FLAGS # Flags .org PRT_OFF,0x90 # Partition table .fill 0x30,0x1,0x0 part4: .byte 0x80, 0x00, 0x01, 0x00 .byte 0xa5, 0xff, 0xff, 0xff .byte 0x00, 0x00, 0x00, 0x00 .byte 0x50, 0xc3, 0x00, 0x00 .word 0xaa55 # Magic number