b0606ca15f
the first sector of the emulated floppy to contain a valid MS-DOS BPB that it can modify. Since boot1 is the first sector of boot.flp, this resulted in the BIOS overwriting part of boot1: specifically the function used to read in sectors from the disk. Submitted by: Mark Peek <mark@whistle.com> Submitted by: Doug Ambrisko <ambrisko@ambrisko.com> PR: i386/26382 Obtained from: NetBSD, OpenBSD (the example BPB) MFC after: 1 month
361 lines
11 KiB
ArmAsm
361 lines
11 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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# Memory Locations
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.set MEM_REL,0x700 # Relocation address
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.set MEM_ARG,0x900 # Arguments
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.set MEM_ORG,0x7c00 # Origin
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.set MEM_BUF,0x8c00 # Load area
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.set MEM_BTX,0x9000 # BTX start
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.set MEM_JMP,0x9010 # BTX entry point
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.set MEM_USR,0xa000 # Client start
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.set BDA_BOOT,0x472 # Boot howto flag
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# Partition Constants
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.set PRT_OFF,0x1be # Partition offset
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.set PRT_NUM,0x4 # Partitions
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.set PRT_BSD,0xa5 # Partition type
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# Flag Bits
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.set FL_PACKET,0x80 # Packet mode
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# Misc. Constants
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.set SIZ_PAG,0x1000 # Page size
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.set SIZ_SEC,0x200 # Sector size
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.globl start
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.globl xread
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.code16
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start: jmp main # Start recognizably
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# This is the start of a standard BIOS Parameter Block (BPB). Most bootable
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# FAT disks have this at the start of their MBR. While normal BIOS's will
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# work fine without this section, IBM's El Torito emulation "fixes" up the
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# BPB by writing into the memory copy of the MBR. Rather than have data
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# written into our xread routine, we'll define a BPB to work around it.
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# The data marked with (T) indicates a field required for a ThinkPad to
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# recognize the disk and (W) indicates fields written from IBM BIOS code.
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# The use of the BPB is based on what OpenBSD and NetBSD implemented in
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# their boot code but the required fields were determined by trial and error.
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#
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# Note: If additional space is needed in boot1, one solution would be to
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# move the "prompt" message data (below) to replace the OEM ID.
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.org 0x03, 0x00
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oemid: .space 0x08, 0x00 # OEM ID
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.org 0x0b, 0x00
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bpb: .word 512 # sector size (T)
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.byte 0 # sectors/clustor
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.word 0 # reserved sectors
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.byte 0 # number of FATs
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.word 0 # root entries
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.word 0 # small sectors
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.byte 0 # media type (W)
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.word 0 # sectors/fat
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.word 18 # sectors per track (T)
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.word 2 # number of heads (T)
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.long 0 # hidden sectors (W)
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.long 0 # large sectors
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.org 0x24, 0x00
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ebpb: .byte 0 # BIOS physical drive number (W)
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.org 0x25,0x90
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#
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# Trampoline used by boot2 to call read to read data from the disk via
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# the BIOS. Call with:
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#
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# %cx:%ax - long - LBA to read in
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# %es:(%bx) - caddr_t - buffer to read data into
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# %dl - byte - drive to read from
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# %dh - byte - num sectors to read
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#
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xread: push %ss # Address
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pop %ds # data
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#
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# Setup an EDD disk packet and pass it to read
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#
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xread.1: # Starting
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pushl $0x0 # absolute
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push %cx # block
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push %ax # number
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push %es # Address of
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push %bx # transfer buffer
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xor %ax,%ax # Number of
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movb %dh,%al # blocks to
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push %ax # transfer
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push $0x10 # Size of packet
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mov %sp,%bp # Packet pointer
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callw read # Read from disk
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lea 0x10(%bp),%sp # Clear stack
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lret # To far caller
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#
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# Load the rest of boot2 and BTX up, copy the parts to the right locations,
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# and start it all up.
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#
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#
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# Setup the segment registers to flat addressing (segment 0) and setup the
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# stack to end just below the start of our code.
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#
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main: cld # String ops inc
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xor %cx,%cx # Zero
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mov %cx,%es # Address
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mov %cx,%ds # data
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mov %cx,%ss # Set up
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mov $start,%sp # stack
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#
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# Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
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# %cx == 0x100.
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#
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mov %sp,%si # Source
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mov $MEM_REL,%di # Destination
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incb %ch # Word count
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rep # Copy
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movsw # code
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#
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# If we are on a hard drive, then load the MBR and look for the first
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# FreeBSD slice. We use the fake partition entry below that points to
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# the MBR when we call nread. The first pass looks for the first active
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# FreeBSD slice. The second pass looks for the first non-active FreeBSD
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# slice if the first one fails.
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#
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mov $part4,%si # Partition
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cmpb $0x80,%dl # Hard drive?
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jb main.4 # No
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movb $0x1,%dh # Block count
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callw nread # Read MBR
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mov $0x1,%cx # Two passes
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main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table
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movb $0x1,%dh # Partition
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main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type?
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jne main.3 # No
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jcxz main.5 # If second pass
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testb $0x80,(%si) # Active?
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jnz main.5 # Yes
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main.3: add $0x10,%si # Next entry
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incb %dh # Partition
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cmpb $0x1+PRT_NUM,%dh # In table?
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jb main.2 # Yes
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dec %cx # Do two
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jcxz main.1 # passes
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#
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# If we get here, we didn't find any FreeBSD slices at all, so print an
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# error message and die.
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#
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mov $msg_part,%si # Message
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jmp error # Error
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#
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# Floppies use partition 0 of drive 0.
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#
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main.4: xor %dx,%dx # Partition:drive
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#
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# Ok, we have a slice and drive in %dx now, so use that to locate and load
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# boot2. %si references the start of the slice we are looking for, so go
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# ahead and load up the first 16 sectors (boot1 + boot2) from that. When
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# we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus,
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# boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00.
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# The first part of boot2 is the disklabel, which is 0x200 bytes long.
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# The second part is BTX, which is thus loaded into 0x9000, which is where
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# it also runs from. The boot2.bin binary starts right after the end of
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# BTX, so we have to figure out where the start of it is and then move the
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# binary to 0xb000. Normally, BTX clients start at MEM_USR, or 0xa000, but
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# when we use btxld create boot2, we use an entry point of 0x1000. That
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# entry point is relative to MEM_USR; thus boot2.bin starts at 0xb000.
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#
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main.5: mov %dx,MEM_ARG # Save args
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movb $0x10,%dh # Sector count
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callw nread # Read disk
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mov $MEM_BTX,%bx # BTX
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mov 0xa(%bx),%si # Get BTX length and set
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add %bx,%si # %si to start of boot2.bin
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mov $MEM_USR+SIZ_PAG,%di # Client page 1
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mov $MEM_BTX+0xe*SIZ_SEC,%cx # Byte
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sub %si,%cx # count
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rep # Relocate
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movsb # client
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sub %di,%cx # Byte count
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xorb %al,%al # Zero assumed bss from
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rep # the end of boot2.bin
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stosb # up to 0x10000
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callw seta20 # Enable A20
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jmp start+MEM_JMP-MEM_ORG # Start BTX
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#
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# Enable A20 so we can access memory above 1 meg.
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#
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seta20: cli # Disable interrupts
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seta20.1: inb $0x64,%al # Get status
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testb $0x2,%al # Busy?
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jnz seta20.1 # Yes
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movb $0xd1,%al # Command: Write
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outb %al,$0x64 # output port
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seta20.2: inb $0x64,%al # Get status
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testb $0x2,%al # Busy?
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jnz seta20.2 # Yes
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movb $0xdf,%al # Enable
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outb %al,$0x60 # A20
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sti # Enable interrupts
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retw # To caller
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#
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# Trampoline used to call read from within boot1.
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#
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nread: mov $MEM_BUF,%bx # Transfer buffer
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mov 0x8(%si),%ax # Get
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mov 0xa(%si),%cx # LBA
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push %cs # Read from
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callw xread.1 # disk
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jnc return # If success, return
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mov $msg_read,%si # Otherwise, set the error
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# message and fall through to
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# the error routine
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#
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# Print out the error message pointed to by %ds:(%si) followed
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# by a prompt, wait for a keypress, and then reboot the machine.
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#
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error: callw putstr # Display message
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mov $prompt,%si # Display
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callw putstr # prompt
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xorb %ah,%ah # BIOS: Get
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int $0x16 # keypress
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movw $0x1234, BDA_BOOT # Do a warm boot
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ljmp $0xffff,$0x0 # reboot the machine
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#
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# Display a null-terminated string using the BIOS output.
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#
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putstr.0: mov $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 char
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testb %al,%al # End of string?
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jne putstr.0 # No
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#
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# Overused return code. ereturn is used to return an error from the
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# read function. Since we assume putstr succeeds, we (ab)use the
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# same code when we return from putstr.
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#
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ereturn: movb $0x1,%ah # Invalid
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stc # argument
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return: retw # To caller
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#
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# Reads sectors from the disk. If EDD is enabled, then check if it is
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# installed and use it if it is. If it is not installed or not enabled, then
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# fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
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# fetch the drive parameters from the BIOS and divide it out ourselves.
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# Call with:
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#
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# %dl - byte - drive number
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# stack - 10 bytes - EDD Packet
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#
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read: push %dx # Save
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movb $0x8,%ah # BIOS: Get drive
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int $0x13 # parameters
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movb %dh,%ch # Max head number
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pop %dx # Restore
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jc return # If error
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andb $0x3f,%cl # Sectors per track
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jz ereturn # If zero
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cli # Disable interrupts
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mov 0x8(%bp),%eax # Get LBA
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push %dx # Save
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movzbl %cl,%ebx # Divide by
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xor %edx,%edx # sectors
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div %ebx # per track
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movb %ch,%bl # Max head number
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movb %dl,%ch # Sector number
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inc %bx # Divide by
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xorb %dl,%dl # number
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div %ebx # of heads
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movb %dl,%bh # Head number
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pop %dx # Restore
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cmpl $0x3ff,%eax # Cylinder number supportable?
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sti # Enable interrupts
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ja read.7 # No, try EDD
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xchgb %al,%ah # Set up cylinder
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rorb $0x2,%al # number
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orb %ch,%al # Merge
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inc %ax # sector
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xchg %ax,%cx # number
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movb %bh,%dh # Head number
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subb %ah,%al # Sectors this track
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mov 0x2(%bp),%ah # Blocks to read
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cmpb %ah,%al # To read
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jb read.2 # this
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movb %ah,%al # track
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read.2: mov $0x5,%di # Try count
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read.3: les 0x4(%bp),%bx # Transfer buffer
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push %ax # Save
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movb $0x2,%ah # BIOS: Read
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int $0x13 # from disk
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pop %bx # Restore
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jnc read.4 # If success
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dec %di # Retry?
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jz read.6 # No
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xorb %ah,%ah # BIOS: Reset
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int $0x13 # disk system
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xchg %bx,%ax # Block count
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jmp read.3 # Continue
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read.4: movzbw %bl,%ax # Sectors read
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add %ax,0x8(%bp) # Adjust
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jnc read.5 # LBA,
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incw 0xa(%bp) # transfer
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read.5: shlb %bl # buffer
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add %bl,0x5(%bp) # pointer,
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sub %al,0x2(%bp) # block count
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ja read # If not done
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read.6: retw # To caller
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read.7: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
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jz ereturn # No, so return an error
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mov $0x55aa,%bx # Magic
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push %dx # Save
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movb $0x41,%ah # BIOS: Check
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int $0x13 # extensions present
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pop %dx # Restore
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jc return # If error, return an error
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cmp $0xaa55,%bx # Magic?
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jne ereturn # No, so return an error
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testb $0x1,%cl # Packet interface?
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jz ereturn # No, so return an error
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mov %bp,%si # Disk packet
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movb $0x42,%ah # BIOS: Extended
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int $0x13 # read
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retw # To caller
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# Messages
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msg_read: .asciz "Read"
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msg_part: .asciz "Boot"
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prompt: .asciz " error\r\n"
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flags: .byte FLAGS # Flags
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.org PRT_OFF,0x90
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# Partition table
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.fill 0x30,0x1,0x0
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part4: .byte 0x80, 0x00, 0x01, 0x00
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.byte 0xa5, 0xff, 0xff, 0xff
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.byte 0x00, 0x00, 0x00, 0x00
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.byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
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.word 0xaa55 # Magic number
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