# # 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. # # $Id: boot1.s,v 1.7 1999/01/10 13:29:51 peter Exp $ .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 start: jmp main # Start recognizably .org 0x4,0x90 # External read from disk xread: pushl %ecx # Set pushl %eax # LBA pushl %es # Set transfer pushl %ebx # buffer pushl %edx # Set count:drive callwi(read) # Read from disk popl %edx # Pop all popl %ebx # registers popl %es # pushed, but popl %ecx # preserve popl %ecx # AX lret # To far caller # Bootstrap main: cld # String ops inc xorl %ecx,%ecx # Zero movl %cx,%es # Address movl %cx,%ds # data movl %cx,%ss # Set up movwir(start,_sp) # stack movl %esp,%esi # Source movwir(MEM_REL,_di) # Destination incb %ch # Word count rep # Copy movsl # code movwir(part4,_si) # Partition cmpb $0x80,%dl # Hard drive? jb main.4 # No movb $0x1,%dh # Block count callwi(nread) # Read MBR movwir(0x1,_cx) # Two passes main.1: movwir(MEM_BUF+PRT_OFF,_si) # Partition table movb $0x1,%dh # Partition main.2: cmpbi1(PRT_BSD,0x4,_si_) # Our partition type? jne main.3 # No jecxz main.5 # If second pass tstbi0(0x80,_si_) # Active? jnz main.5 # Yes main.3: addl $0x10,%esi # Next entry incb %dh # Partition cmpb $0x1+PRT_NUM,%dh # In table? jb main.2 # Yes decl %ecx # Do two jecxz main.1 # passes movwir(msg_part,_si) # Message jmp error # Error main.4: xorl %edx,%edx # Partition:drive main.5: movwrm(_dx,MEM_ARG) # Save args movb $0x10,%dh # Sector count callwi(nread) # Read disk movwir(MEM_BTX,_bx) # BTX movw1r(0xa,_bx_,_si) # Point past addl %ebx,%esi # it movwir(MEM_USR+SIZ_PAG,_di) # Client page 1 movwir(MEM_BTX+0xe*SIZ_SEC,_cx) # Byte subl %esi,%ecx # count rep # Relocate movsb # client subl %edi,%ecx # Byte count xorb %al,%al # Zero rep # assumed stosb # bss callwi(seta20) # Enable A20 jmpnwi(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 ret # To caller # Local read from disk nread: movwir(MEM_BUF,_bx) # Transfer buffer movw1r(0x8,_si_,_ax) # Get movw1r(0xa,_si_,_cx) # LBA pushl %cs # Read from callwi(xread) # disk jnc return # If success movwir(msg_read,_si) # Message # Error exit error: callwi(putstr) # Display message movwir(prompt,_si) # Display callwi(putstr) # prompt xorb %ah,%ah # BIOS: Get int $0x16 # keypress int $0x19 # BIOS: Reboot # Display string putstr.0: movwir(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: ret # To caller # Read from disk read: movl %esp,%ebp # Address stack frame pushl %edx # Save movb $0x8,%ah # BIOS: Get drive int $0x13 # parameters movb %dh,%ch # Max head number popl %edx # Restore jc return # If error andb $0x3f,%cl # Sectors per track jz ereturn # If zero cli # Disable interrupts o16 # Get movw1r(0x8,_bp_,_ax) # LBA pushl %edx # Save movzbw %cl,%bx # Divide by xorw %dx,%dx # sectors divw %bx,%ax # per track movb %ch,%bl # Max head number movb %dl,%ch # Sector number incl %ebx # Divide by xorb %dl,%dl # number divw %bx,%ax # of heads movb %dl,%bh # Head number popl %edx # Restore o16 # Cylinder number cmpl $0x3ff,%eax # supportable? sti # Enable interrupts ja ereturn # No xchgb %al,%ah # Set up cylinder rorb $0x2,%al # number orb %ch,%al # Merge incl %eax # sector xchgl %eax,%ecx # number movb %bh,%dh # Head number subb %ah,%al # Sectors this track movb1r(0x3,_bp_,_ah) # Blocks to read cmpb %ah,%al # To read jb read.1 # this movb %ah,%al # track read.1: movwir(0x5,_di) # Try count read.2: lesw1r(0x4,_bp_,_bx) # Transfer buffer pushl %eax # Save movb $0x2,%ah # BIOS: Read int $0x13 # from disk popl %ebx # Restore jnc read.3 # If success decl %edi # Retry? jz read.5 # No xorb %ah,%ah # BIOS: Reset int $0x13 # disk system xchgl %ebx,%eax # Block count jmp read.2 # Continue read.3: movzbl %bl,%eax # Sectors read addwr1(_ax,0x8,_bp_) # Adjust jnc read.4 # LBA, incw1(0xa,_bp_) # transfer read.4: shlb %bl # buffer addbr1(_bl,0x5,_bp_) # pointer, subbr1(_al,0x3,_bp_) # block count ja read # If not done read.5: ret # To caller # Messages msg_read: .asciz "Read" msg_part: .asciz "Boot" prompt: .asciz " error\r\n" .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