minix/boot/jumpboot.s

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2005-04-21 16:53:53 +02:00
! jumpboot 1.0 - Jump to another bootstrap Author: Kees J. Bot
! 14 Apr 1999
!
! This code may be placed into any free boot sector, like the first sector
! of an extended partition, a file system partition other than the root,
! or even the master bootstrap. It will load and run another bootstrap whose
! disk, partition, and slice number (not necessarily all three) are patched
! into this code by installboot. If the ALT key is held down when this code
! is booted then you can type the disk, partition, and slice numbers manually.
! The manual interface is default if no numbers are patched in by installboot.
!
o32 = 0x66 ! This assembler doesn't know 386 extensions
LOADOFF = 0x7C00 ! 0x0000:LOADOFF is where this code is loaded
BUFFER = 0x0600 ! First free memory
PART_TABLE = 446 ! Location of partition table within master
PENTRYSIZE = 16 ! Size of one partition table entry
MAGIC = 510 ! Location of the AA55 magic number
! <ibm/partition.h>:
MINIX_PART = 0x81
sysind = 4
lowsec = 8
.text
! Find and load another bootstrap and jump to it.
jumpboot:
xor ax, ax
mov ds, ax
mov es, ax
cli
mov ss, ax ! ds = es = ss = Vector segment
mov sp, #LOADOFF
sti
! Move this code to safety, then jump to it.
mov si, sp ! si = start of this code
mov di, #BUFFER ! di = Buffer area
mov cx, #512/2 ! One sector
cld
rep movs
jmpf BUFFER+migrate, 0 ! To safety
migrate:
mov bp, #BUFFER+guide ! Patched guiding characters
altkey:
movb ah, #0x02 ! Keyboard shift status
int 0x16
testb al, #0x08 ! Bit 3 = ALT key
jz noalt ! ALT key pressed?
again:
mov bp, #zero ! Ignore patched stuff
noalt:
! Follow guide characters to find the boot partition.
call print
.ascii "d?\b\0" ! Initial greeting
! Disk number?
disk:
movb dl, #0x80 - 0x30 ! Prepare to add an ASCII digit
call getch ! Get number to tell which disk
addb dl, al ! dl = 0x80 + (al - '0')
jns n0nboot ! Result should be >= 0x80
mov si, #BUFFER+zero-lowsec ! si = where lowsec(si) is zero
cmpb (bp), #0x23 ! Next guide character is '#'?
jne notlogical
lea si, 1-lowsec(bp) ! Logical sector offset follows '#'
notlogical:
call load ! Load chosen sector of chosen disk
cmpb (bp), #0x23
je boot ! Run bootstrap if a logical is chosen
call print ! Intro to partition number
.ascii "p?\b\0"
part:
call getch ! Get character to tell partition
call gettable ! Get partition table
call sort ! Sort partition table
call choose_load ! Compute chosen entry and load
cmpb sysind(si), #MINIX_PART ! Minix subpartition table possible?
jne waitboot
call print ! Intro to slice number
.ascii "s?\b\0"
slice:
call getch ! Get character to tell slice
call gettable ! Get partition table
call choose_load ! Compute chosen entry and load
waitboot:
call print ! Intro to nothing
.ascii " ?\b\0"
call getch ! Supposed to type RETURN now
n0nboot:jmp nonboot ! Sorry, can't go further
! Get a character, either the patched-in, or one from the keyboard.
getch:
movb al, (bp) ! Get patched-in character
testb al, al
jz getkey
inc bp
jmp gotkey
getkey: xorb ah, ah ! Wait for keypress
int 0x16
gotkey: testb dl, dl ! Ignore CR if disk number not yet set
jns putch
cmpb al, #0x0D ! Carriage return?
je boot
!jmp putch
! Print a character
putch: movb ah, #0x0E ! Print character in teletype mode
mov bx, #0x0001 ! Page 0, foreground color
int 0x10
ret
! Print a message.
print: mov cx, si ! Save si
pop si ! si = String following 'call print'
prnext: lodsb ! al = *si++ is char to be printed
testb al, al ! Null marks end
jz prdone
call putch
jmp prnext
prdone: xchg si, cx ! Restore si
jmp (cx) ! Continue after the string
! Return typed (or in patched data) means to run the bootstrap now in core!
boot:
call print ! Make line on screen look proper
.ascii "\b \r\n\0"
jmp LOADOFF-BUFFER ! Jump to LOADOFF
! Compute address of chosen partition entry from choice al into si, then
! continue to load the boot sector of that partition.
choose_load:
subb al, #0x30 ! al -= '0'
cmpb al, #4 ! Only four partitions
ja n0nboot
movb ah, #PENTRYSIZE
mulb ah ! al *= PENTRYSIZE
add ax, #BUFFER+PART_TABLE
mov si, ax ! si = &part_table[al - '0']
movb al, sysind(si) ! System indicator
testb al, al ! Unused partition?
jz n0nboot
!jmp load ! Continue to load boot sector
! Load boot sector of the current partition.
load:
push dx ! Save drive code
push es ! Next call sets es
movb ah, #0x08 ! Code for drive parameters
int 0x13
pop es
andb cl, #0x3F ! cl = max sector number (1-origin)
incb dh ! dh = 1 + max head number (0-origin)
movb al, cl ! al = cl = sectors per track
mulb dh ! dh = heads, ax = heads * sectors
mov bx, ax ! bx = sectors per cylinder = heads * sectors
mov ax, lowsec+0(si)
mov dx, lowsec+2(si) ! dx:ax = sector within drive
cmp dx, #[1024*255*63-255]>>16 ! Near 8G limit?
jae bigdisk
div bx ! ax = cylinder, dx = sector within cylinder
xchg ax, dx ! ax = sector within cylinder, dx = cylinder
movb ch, dl ! ch = low 8 bits of cylinder
divb cl ! al = head, ah = sector (0-origin)
xorb dl, dl ! About to shift bits 8-9 of cylinder into dl
shr dx, #1
shr dx, #1 ! dl[6..7] = high cylinder
orb dl, ah ! dl[0..5] = sector (0-origin)
movb cl, dl ! cl[0..5] = sector, cl[6..7] = high cyl
incb cl ! cl[0..5] = sector (1-origin)
pop dx ! Restore drive code in dl
movb dh, al ! dh = al = head
mov bx, #LOADOFF ! es:bx = where sector is loaded
mov ax, #0x0201 ! ah = Code for read / al = one sector
int 0x13
jmp rdeval ! Evaluate read result
bigdisk:
mov bx, dx ! bx:ax = dx:ax = sector to read
pop dx ! Restore drive code in dl
push si ! Save si
mov si, #BUFFER+ext_rw ! si = extended read/write parameter packet
mov 8(si), ax ! Starting block number = bx:ax
mov 10(si), bx
movb ah, #0x42 ! Extended read
int 0x13
pop si ! Restore si to point to partition entry
!jmp rdeval
rdeval:
jnc rdok
rderr:
call print
.ascii "\r\nRead error\r\n\0"
jmp again
rdok:
cmp LOADOFF+MAGIC, #0xAA55
je sigok ! Signature ok?
nonboot:
call print
.ascii "\r\nNot bootable\r\n\0"
jmp again
sigok:
ret
! Get the partition table into my space.
gettable:
mov si, #LOADOFF+PART_TABLE
mov di, #BUFFER+PART_TABLE
mov cx, #4*PENTRYSIZE/2
rep movs
ret
! Sort the partition table.
sort:
mov cx, #4 ! Four times is enough to sort
bubble: mov si, #BUFFER+PART_TABLE ! First table entry
bubble1:lea di, PENTRYSIZE(si) ! Next entry
cmpb sysind(si), ch ! Partition type, nonzero when in use
jz exchg ! Unused entries sort to the end
inuse: mov bx, lowsec+0(di)
sub bx, lowsec+0(si) ! Compute di->lowsec - si->lowsec
mov bx, lowsec+2(di)
sbb bx, lowsec+2(si)
jae order ! In order if si->lowsec <= di->lowsec
exchg: movb bl, (si)
xchgb bl, PENTRYSIZE(si) ! Exchange entries byte by byte
movb (si), bl
inc si
cmp si, di
jb exchg
order: mov si, di
cmp si, #BUFFER+PART_TABLE+3*PENTRYSIZE
jb bubble1
loop bubble
ret
.data
! Extended read/write commands require a parameter packet.
ext_rw:
.data1 0x10 ! Length of extended r/w packet
.data1 0 ! Reserved
.data2 1 ! Blocks to transfer (just one)
.data2 LOADOFF ! Buffer address offset
.data2 0 ! Buffer address segment
.data4 0 ! Starting block number low 32 bits (tbfi)
zero: .data4 0 ! Starting block number high 32 bits
.align 2
guide:
! Guide characters and possibly a logical partition number patched here by
! installboot, up to 6 bytes maximum.