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|
!
! This is floppy bootblock to load the first item from a tar file.
!
! The tar file is constructed with a GNU TAR label at the start
! which is replaced with this by the makeboot.c program.
!
! The first item must be a Linux-8086 executable compiled with the -Ms option
!
! Copyright (C) 1996 Robert de Bath, distributed under the GPL Version 2.
!
BOOTADDR= 0x7C00 ! The address that the boot seg is loaded.
RELADDR = 0x0600 ! This is floppy, so we can relocate to 'super' address
! It appears the 0500 is also ok as that's DOS memory
! But then where can we get 200 bytes of stack!
STACK = 0x0600 ! Inital stack, 0 makes bad_magic
LOADSEG = 0x0080 ! Segment for program load, this must be 512b aligned
! The first 32 bytes are the a.out header.
DEBUG=1 ! Print dots ...
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
macro locn
if *-start>?1
fail! ?1
endif
.blkb ?1 + start-*
mend
! On startup from a floppy boot it`s probably best if we assume _nothing_
! that we don`t have to ...
!
! So, `start` is, erm, right here :-)
! The boot block is re-loaded from the floppy for relocation.
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
use16
org RELADDR
start:
! Don't even _think_ of changing this unless you're 110% sure!
.byte 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90
.byte 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90
block start
.asciz "ENIAC"
.byte $C0
endb
! All right, I'll help, you can use any of these chars:
! "/?@ABCDEFGHIJKLMNO"
! Others are likely to cause ... problems.
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
! Beware; the assumption is this code is relocatable.
xor ax,ax
mov ds,ax
mov es,ax
mov ss,ax
if STACK = 0
mov sp,ax
else
mov sp,#STACK ! Stack location
endif
cld
! ASSUME ds=ss=es=cs=0
keep_trying1:
! Get the tar block after this program, and relocate this code.
mov ax,#$0202 ! Read 2 sectors
mov bx,#start ! Where this _should_ be
mov cx,#$0001 ! From sector 1
xor dx,dx ! Of the floppy drive head zero
int $13
jc keep_trying1
jmpi going,#0
going:
! OK. Code will now be run at correct address.
if DEBUG
call pboot
endif
mov al,tar_link
cmp al,#'0
jnz nogood ! Make sure next item is file.
call probe_floppy
call get_size ! Get number of clicks in di
cmp di,#0
jz nogood ! If it`s zero .. Hmm
if STACK = 0
mov sp,#bad_magic ! Real bad magic :-)
endif
call load_sectors
! This requires that we have been relocated, so we can't call it too soon.
nogood:
push cs
pop es
hcode:
mov ax,#$0201 ! Read 1 sector
mov bx,#BOOTADDR ! into the boot area
mov cx,#1 ! sector 1
mov dx,#$0080 ! hard drive head zero
int $13
jc hcode ! Keep trying forever!
jmpi BOOTADDR,#0
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! These are the number of sectors per track that will be scanned for.
! For 3.5 inch floppies 36 is 2.88 Mb, 18 is 1.44Mb, 21 is 1.68Mb on
! a 1.44Mb floppy drive. 15 and 9 are for 5.25 inch floppies.
disksizes: .byte 36,21,18,15,9
! End of part 1
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
! This is important bits of the TAR Block.
! The chksum field will need to be changed if any mods are done to this
! file so that the bare header is a TAR file. If it's installed using
! makeboot that program will correct the sum as it also changes the time.
locn(100)
blk_mode: .asciz " 4111"
blk_uid: .blkb 8
blk_gid: .blkb 8
blk_size: .blkb 12
blk_mtime: .asciz "6141567743 "
if DEBUG
blk_chksum: .asciz " 142273"
else
blk_chksum: .asciz " 127270"
endif
blk_link: .byte 'V
! Sneaks here, overlay zero init vars on tar data.
block blk_mode
public sectors
sectors: .blkw 1 !
bios_disk: .blkb 12 ! BPB for FD0
head: .word 0 ! current head
track: .word 0 ! current track
endb
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! This code taken from the Linux bootsector and adjusted to suit
!
! Many BIOS's default disk parameter tables will not
! recognize multi-sector reads beyond the maximum sector number
! specified in the default diskette parameter tables - this may
! mean 7 sectors in some cases.
!
! Since single sector reads are slow and out of the question,
! we must take care of this by creating new parameter tables
! (for the first disk) in RAM. We will set the maximum sector
! count to 36 - the most we will encounter on an ED 2.88.
!
! High doesn't hurt. Low does.
!
! Segments are as follows: ds=es=ss=cs=0
!
probe_floppy:
mov di,#bios_disk
mov bx,#0x78
! 0:bx is parameter table address
push ds
lds si,[bx]
! ds:si is source
mov cl,#6
! copy 12 bytes
cld
push di
rep
movsw
pop di
pop ds
movb 4[di],*36 ! patch sector count
mov [bx],di
mov 2[bx],es
! It seems that there is no BIOS call to get the number of sectors. Guess
! 36 sectors if sector 36 can be read, 18 sectors if sector 18 can be read,
! 15 if sector 15 can be read. Otherwise guess 9.
mov si,#disksizes ! table of sizes to try
probe_loop:
lodsb
cbw ! extend to word
mov sectors, ax
cmp al,#9
je got_sectors ! if all else fails, try 9
xchg ax, cx ! cx = track and sector
xor dx, dx ! drive 0, head 0
mov bx,#probe_buf ! address after setup (es = cs)
mov ax,#0x0201 ! service 2, 1 sector
int 0x13
jc probe_loop ! try next value
got_sectors:
ret
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! This function reads the size of the first file in the TAR image. It's
! stored in octal in the tar header that was loaded just after this block.
get_size:
mov di,#tar_size
xor dx,dx
xor bx,bx
xor cx,cx
next_dig:
mov al,[di]
and al,#$F8
cmp al,#'0
jne no_dig
mov al,[di]
and al,#$07
mov cl,#3
mul_loop:
sal bx,#1 ! Double prec * 8
rcl dx,#1
loop mul_loop
or bl,al
no_dig:
inc di
cmp di,#tar_mtime
jne next_dig
add bx,#15 ! How many clicks ?
adc dx,cx ! AKA zero
mov cl,#4
div_loop:
shr dx,#1
rcr bx,#1
loop div_loop
mov di,bx
bad_magic:
ret
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! This is good so far, is it an 8086 a.out file ?
! If so start it.
go_go_go:
xor dx,dx ! DX=0 => floppy drive
push dx ! CX=0 => partition offset = 0
mov si,[sectors] ! Save for monitor.out
mov bx,#LOADSEG
mov ds,bx ! DS = loadaddress
inc bx
inc bx ! bx = initial CS
xor di,di ! Zero
mov ax,[di]
cmp ax,#0x0301 ! Right magic ?
jnz bad_magic ! Yuk ...
mov ax,[di+2]
and ax,#$20 ! Is it split I/D ?
jz impure ! No ...
mov cl,#4
mov ax,[di+8]
shr ax,cl
impure:
pop cx ! Partition offset.
add ax,bx
mov ss,ax
mov sp,[di+24] ! Chmem value
mov ds,ax
push bx ! jmpi 0,#LOADSEG+2
push di
! AX=ds, BX=cs, CX=X, DX=X, SI=X, DI=0, BP=X, ES=X, DS=*, SS=*, CS=*
retf
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
! This isn't in a normal volume lable, no problem it leaves more space.
!
! locn(257)
! blk_magic: .ascii "ustar "
! .blkb 1
! blk_uname: .ascii "TarBoot/Copyright"
! blk_uname_end:
! .blkb 32+blk_uname-blk_uname_end
! blk_gname: .ascii "R de Bath"
! blk_gname_end:
! .blkb 32+blk_gname-blk_gname_end
! blk_devmaj: .blkb 8
! blk_devmin: .blkb 8
!
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
if DEBUG
dot: mov al,#'.
putc:
push bx
mov bx,#7
mov ah,#$E
int $10
pop bx
ret
endif
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! This code taken from the Linux bootsector and adjusted to suit
!
! This routine loads the system at address LOADSEG, making sure
! no 64kB boundaries are crossed. We try to load it as fast as
! possible, loading whole tracks whenever we can.
!
! LOADSEG must be sector aligned and sectors will be loaded upto
! the next 64k boundry past the segment specified by DI.
load_sectors:
if LOADSEG & $F000 = 0
xor ax,ax
else
mov ax,#LOADSEG & $F000 ! segment to load to
endif
mov es,ax
! dx=sectors read of current track
! bx=offset in memory of block
! si=sectors read to block
! al=number to read
read_it:
mov dx,#2 ! Volume lable + tar header
if LOADSEG & $0FFF = 0
xor si,si
else
mov si,#(LOADSEG & $FFF)>>5
endif
add di,#LOADSEG
rp_read:
if DEBUG
call dot
endif
mov ax,es
cmp ax,di ! have we loaded all yet?
jbe ok1_read
jmp go_go_go ! Loaded, run it.
ok1_read:
mov ax,sectors ! nr of sectors/track
sub ax,dx ! remaining of track
mov cx,ax ! cx= remaining
add cx,si ! boundary check
cmp cl,#128
jbe ok2_read !
! to much-> fill block
mov ax,#128 ! ax=0
sub ax,si ! so much may be read
ok2_read:
mov bx,si
mov cx,#9
shl bx,cl
call read_track ! do it
mov cx,ax ! cl=read blocks
add ax,dx ! ax=new sectors
cmp ax,sectors ! track done?
jne ok3_read
mov ax,#1 ! yes
sub ax,head
jne ok4_read ! next head
inc track ! next track
ok4_read:
mov head,ax
xor ax,ax
ok3_read:
mov dx,ax
add si,cx
cmp si,#128
jne rp_read
mov ax,es
add ah,#0x10
mov es,ax
xor si,si
jmp rp_read
read_track:
push dx
push ax
push bx
mov cx,dx
mov dx,track
inc cx
mov ch,dl
mov dx,head
mov dh,dl
and dx,#0x0100
mov ah,#2
int 0x13
! ah=02h al=nr sectors to read
! ch=cylinder
! cl=sector
! dh=head
! dl=drive
! es:bx=buffer
jc bad_rt
pop bx
pop ax
pop dx
ret
bad_rt: xor ah,ah
xor dl,dl
int 0x13
pop bx
pop ax
pop dx
jmp read_track
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
!
! This is the GNU-TAR 'isextended' field. It must be zero or gtar goes apeshit.
locn(482)
.byte 0
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
if DEBUG
pboot:
mov si,#mesg
nextc:
lodsb
call putc
cmp al,#0
jnz nextc
ret
locn(512-16)
mesg:
.ascii "Tarboot loading "
endif
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
! This isn't a hard disk boot sector so don't give it an HD magic
! locn(510)
! .word 0xAA55
if DEBUG = 0
locn(510)
.word 0
endif
! From here down is where we load stuff.
locn(512)
blk_load: ! Address of block load
tar_name: .blkb 100
tar_mode: .blkb 8
tar_uid: .blkb 8
tar_gid: .blkb 8
tar_size: .blkb 12
tar_mtime: .blkb 12
tar_chksum: .blkb 8
tar_link: .blkb 1 ! "0"
tar_linkname: .blkb 100
tar_magic: .blkb 8 ! "ustar "
tar_uname: .blkb 32
tar_gname: .blkb 32
tar_devmaj: .blkb 8
tar_devmin: .blkb 8
tar_padd:
locn(1024)
probe_buf: .blkb 512
|