# # 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 1.3 1998/10/27 20:19:24 rnordier Exp $ .set MEM_REL,0x600 # Relocation address .set MEM_ARG,0x800 # Arguments .set MEM_PKT,0x810 # Disk packet .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 xread: pushl %cs # Address popl %ds # data xread.1: movwir(MEM_PKT,_si) # Packet movbr1(_al,0x2,_si_) # Blocks to read o16 # Transfer movwr1(_bx,0x4,_si_) # buffer o16 # LBA movwr1(_cx,0x8,_si_) # address callwi(read) # Read from disk lret # To caller main: cld # String ops inc xorl %eax,%eax # Zero movl %ax,%es # Address movl %ax,%ds # data movl %ax,%ss # Set up movwir(start,_sp) # stack movl %esp,%esi # Source movwir(MEM_REL,_di) # Destination movwir(0x100,_cx) # Word count rep # Copy movsl # code movb $0x10,%cl # Words to clear rep # Zero stosl # them movbi1(0x10,-0x10,_di_) # Set packet size cmpb $0x80,%dl # Hard drive? jb main.4 # No movwir(part4,_si) # Read master movb $0x1,%al # boot callwi(nread) # record xorl %eax,%eax # Pass number 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 tstbi0(0x80,_si_) # Active? jnz main.5 # Yes testb %al,%al # Second pass? jnz main.5 # Yes main.3: addl $0x10,%esi # Next entry incb %dh # Partition cmpb $0x1+PRT_NUM,%dh # Done? jb main.2 # No incl %eax # Pass cmpb $0x2,%al # Done? jb main.1 # No movwir(msg_part,_si) # Message jmp error # Error main.4: xorl %edx,%edx # Partition:drive movwir(part4,_si) # Partition pointer main.5: movwrm(_dx,MEM_ARG) # Save args movb $0x10,%al # 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 # Read from disk nread: xorw %bx,%bx # Transfer movb $MEM_BUF>>0x8,%bh # buffer o16 # LBA movw1r(0x8,_si_,_cx) # address pushl %cs # Read from callwi(xread.1) # disk jnc return # If success movwir(msg_read,_si) # Message # Error exit error: callwi(putstr) # Display message movwir(msg_boot,_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 return: ret # Generic return # Read from disk read: tstbim(0x80,MEM_REL+flags-start)# Extensions enabled? jz read.3 # No testb %dh,%dh # Try for extensions? jz read.3 # No movwir(0x55aa,_bx) # Magic pushl %edx # Save movb $0x41,%ah # BIOS: Check int $0x13 # extensions present popl %edx # Restore jc read.3 # If error cmpwir(0xaa55,_bx) # Magic? jne read.3 # No testb $0x1,%cl # Packet interface? jz read.3 # No movb $0x42,%ah # BIOS: Extended int $0x13 # read ret # To caller read.1: movb $0x1,%ah # Invalid stc # parameter read.2: ret # To caller read.3: pushl %edx # Save movb $0x8,%ah # BIOS: Get drive int $0x13 # parameters movb %dh,%ch # Max head number popl %edx # Restore jc read.2 # If error andb $0x3f,%cl # Sectors per track jz read.1 # If zero o16 # Get movw1r(0x8,_si_,_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 of divw %bx,%ax # heads movb %dl,%bh # Head number popl %edx # Restore o16 # Cylinder number cmpl $0x3ff,%eax # supportable? ja read.1 # 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(0x2,_si_,_ah) # Blocks to read cmpb %ah,%al # To read jb read.4 # this movb %ah,%al # track read.4: movwir(0x5,_bp) # Try count read.5: lesw1r(0x4,_si_,_bx) # Transfer buffer pushl %eax # Save movb $0x2,%ah # BIOS: Conventional int $0x13 # read popl %ebx # Restore jnc read.6 # If success decl %ebp # Retry? jz read.7 # No xorb %ah,%ah # BIOS: Reset int $0x13 # disk system movl %ebx,%eax # Block count jmp read.5 # Continue read.6: movzbw %bl,%ax # Sectors read o16 # Adjust addwr1(_ax,0x8,_si_) # LBA, shlb %bl # buffer addbr1(_bl,0x5,_si_) # pointer, subbr1(_al,0x2,_si_) # block count ja read.3 # If not done read.7: ret # To caller # Messages msg_read: .asciz "Read error" msg_part: .asciz "No bootable partition" msg_boot: .asciz "\r\nHit return to reboot: " 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