#
# 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.
#
# $Id$
# Memory Locations
.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 BDA_BOOT,0x472 # Boot howto flag
# Partition Constants
.set PRT_OFF,0x1be # Partition offset
.set PRT_NUM,0x4 # Partitions
.set PRT_UBX,0x2A # Partition type
# Flag Bits
.set FL_PACKET,0x80 # Packet mode
# Misc. Constants
.set SIZ_PAG,0x1000 # Page size
.set SIZ_SEC,0x200 # Sector size
.globl start
.globl xread
.code16
start: jmp main # Start recognizably
# This is the start of a standard BIOS Parameter Block (BPB). Most bootable
# FAT disks have this at the start of their MBR. While normal BIOS's will
# work fine without this section, IBM's El Torito emulation "fixes" up the
# BPB by writing into the memory copy of the MBR. Rather than have data
# written into our xread routine, we'll define a BPB to work around it.
# The data marked with (T) indicates a field required for a ThinkPad to
# recognize the disk and (W) indicates fields written from IBM BIOS code.
# The use of the BPB is based on what OpenBSD and NetBSD implemented in
# their boot code but the required fields were determined by trial and error.
#
# Note: If additional space is needed in boot1, one solution would be to
# move the "prompt" message data (below) to replace the OEM ID.
.org 0x03, 0x00
oemid: .space 0x08, 0x00 # OEM ID
.org 0x0b, 0x00
bpb: .word 512 # sector size (T)
.byte 0 # sectors/clustor
.word 0 # reserved sectors
.byte 0 # number of FATs
.word 0 # root entries
.word 0 # small sectors
.byte 0 # media type (W)
.word 0 # sectors/fat
.word 18 # sectors per track (T)
.word 2 # number of heads (T)
.long 0 # hidden sectors (W)
.long 0 # large sectors
.org 0x24, 0x00
ebpb: .byte 0 # BIOS physical drive number (W)
.org 0x25,0x90
#
# Trampoline used by boot2 to call read to read data from the disk via
# the BIOS. Call with:
#
# %cx:%ax - long - LBA to read in
# %es:(%bx) - caddr_t - buffer to read data into
# %dl - byte - drive to read from
# %dh - byte - num sectors to read
#
xread: push %ss # Address
pop %ds # data
#
# Setup an EDD disk packet and pass it to read
#
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
#
# Load the rest of boot2 and BTX up, copy the parts to the right locations,
# and start it all up.
#
#
# Setup the segment registers to flat addressing (segment 0) and setup the
# stack to end just below the start of our code.
#
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
#
# Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
# %cx == 0x100.
#
mov %sp,%si # Source
mov $MEM_REL,%di # Destination
incb %ch # Word count
rep # Copy
movsw # code
#
# If we are on a hard drive, then load the MBR and look for the first
# UbixOS slice. We use the fake partition entry below that points to
# the MBR when we call nread. The first pass looks for the first active
# UbixOS slice. The second pass looks for the first non-active UbixOS
# slice if the first one fails.
#
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_UBX,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
#
# If we get here, we didn't find any UbixOS slices at all, so print an
# error message and die.
#
mov $msg_part,%si # Message
jmp error # Error
#
# Floppies use partition 0 of drive 0.
#
main.4: xor %dx,%dx # Partition:drive
#
# Ok, we have a slice and drive in %dx now, so use that to locate and load
# boot2. %si references the start of the slice we are looking for, so go
# ahead and load up the first 16 sectors (boot1 + boot2) from that. When
# we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus,
# boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00.
# The first part of boot2 is the disklabel, which is 0x200 bytes long.
# The second part is BTX, which is thus loaded into 0x9000, which is where
# it also runs from. The boot2.bin binary starts right after the end of
# BTX, so we have to figure out where the start of it is and then move the
# binary to 0xb000. Normally, BTX clients start at MEM_USR, or 0xa000, but
# when we use btxld create boot2, we use an entry point of 0x1000. That
# entry point is relative to MEM_USR; thus boot2.bin starts at 0xb000.
#
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 # Get BTX length and set
add %bx,%si # %si to start of boot2.bin
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 assumed bss from
rep # the end of boot2.bin
stosb # up to 0x10000
callw seta20 # Enable A20
jmp start+MEM_JMP-MEM_ORG # Start BTX
#
# Enable A20 so we can access memory above 1 meg.
#
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
#
# Trampoline used to call read from within boot1.
#
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, return
mov $msg_read,%si # Otherwise, set the error
# message and fall through to
# the error routine
#
# Print out the error message pointed to by %ds:(%si) followed
# by a prompt, wait for a keypress, and then reboot the machine.
#
error: callw putstr # Display message
mov $prompt,%si # Display
callw putstr # prompt
xorb %ah,%ah # BIOS: Get
int $0x16 # keypress
movw $0x1234, BDA_BOOT # Do a warm boot
ljmp $0xffff,$0x0 # reboot the machine
#
# Display a null-terminated string using the BIOS output.
#
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
#
# Overused return code. ereturn is used to return an error from the
# read function. Since we assume putstr succeeds, we (ab)use the
# same code when we return from putstr.
#
ereturn: movb $0x1,%ah # Invalid
stc # argument
return: retw # To caller
#
# Reads sectors from the disk. If EDD is enabled, then check if it is
# installed and use it if it is. If it is not installed or not enabled, then
# fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
# fetch the drive parameters from the BIOS and divide it out ourselves.
# Call with:
#
# %dl - byte - drive number
# stack - 10 bytes - EDD Packet
#
read: 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 read.7 # No, try EDD
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 # If not done
read.6: retw # To caller
read.7: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
jz ereturn # No, so return an error
mov $0xbeba,%bx # Magic
push %dx # Save
movb $0x41,%ah # BIOS: Check
int $0x13 # extensions present
pop %dx # Restore
jc return # If error, return an error
cmp $0xbabe,%bx # Magic?
jne ereturn # No, so return an error
testb $0x1,%cl # Packet interface?
jz ereturn # No, so return an error
mov %bp,%si # Disk packet
movb $0x42,%ah # BIOS: Extended
int $0x13 # read
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 0x2A, 0xff, 0xff, 0xff
.byte 0x00, 0x00, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
.word 0xbabe # Magic number
