257 lines
8.4 KiB
ArmAsm
257 lines
8.4 KiB
ArmAsm
#
|
|
! Bootblock 1.5 - Minix boot block. Author: Kees J. Bot
|
|
! 21 Dec 1991
|
|
!
|
|
! When the PC is powered on, it will try to read the first sector of floppy
|
|
! disk 0 at address 0x7C00. If this fails due to the absence of flexible
|
|
! magnetic media, it will read the master boot record from the first sector
|
|
! of the hard disk. This sector not only contains executable code, but also
|
|
! the partition table of the hard disk. When executed, it will select the
|
|
! active partition and load the first sector of that at address 0x7C00.
|
|
! This file contains the code that is eventually read from either the floppy
|
|
! disk, or the hard disk partition. It is just smart enough to load /boot
|
|
! from the boot device into memory at address 0x10000 and execute that. The
|
|
! disk addresses for /boot are patched into this code by installboot as 24-bit
|
|
! sector numbers and 8-bit sector counts above enddata upwards. /boot is in
|
|
! turn smart enough to load the different parts of the Minix kernel into
|
|
! memory and execute them to finally get Minix started.
|
|
!
|
|
|
|
LOADOFF = 0x7C00 ! 0x0000:LOADOFF is where this code is loaded
|
|
BOOTSEG = 0x1000 ! Secondary boot code segment.
|
|
#ifdef CDBOOT
|
|
BOOTOFF = 0x0050 ! Offset into /boot above header
|
|
#else
|
|
BOOTOFF = 0x0030 ! Offset into /boot above header
|
|
#endif
|
|
BUFFER = 0x0600 ! First free memory
|
|
#ifndef CDBOOT /* just constants, but make no sense for CDs */
|
|
LOWSEC = 8 ! Offset of logical first sector in partition
|
|
! table
|
|
|
|
! Variables addressed using bp register
|
|
lowsec = 2 ! Offset of boot partition within drive
|
|
secpcyl = 6 ! Sectors per cylinder = heads * sectors
|
|
#endif
|
|
device = 0 ! The boot device
|
|
|
|
.text
|
|
|
|
! Start boot procedure.
|
|
|
|
boot:
|
|
xor ax, ax ! ax = 0x0000, the vector segment
|
|
mov ds, ax
|
|
cli ! Ignore interrupts while setting stack
|
|
mov ss, ax ! ss = ds = vector segment
|
|
mov sp, #LOADOFF ! Usual place for a bootstrap stack
|
|
sti
|
|
|
|
push ax
|
|
push ax ! Push a zero lowsec(bp)
|
|
|
|
push dx ! Boot device in dl will be device(bp)
|
|
mov bp, sp ! Using var(bp) is one byte cheaper then var.
|
|
|
|
push es
|
|
push si ! es:si = partition table entry if hard disk
|
|
|
|
mov di, #LOADOFF+sectors ! char *di = sectors;
|
|
|
|
#ifndef CDBOOT
|
|
testb dl, dl ! Winchester disks if dl >= 0x80
|
|
jge floppy
|
|
#endif
|
|
|
|
winchester:
|
|
|
|
#ifndef CDBOOT
|
|
! Get the offset of the first sector of the boot partition from the partition
|
|
! table. The table is found at es:si, the lowsec parameter at offset LOWSEC.
|
|
|
|
eseg
|
|
les ax, LOWSEC(si) ! es:ax = LOWSEC+2(si):LOWSEC(si)
|
|
mov lowsec+0(bp), ax ! Low 16 bits of partitions first sector
|
|
mov lowsec+2(bp), es ! High 16 bits of partitions first sector
|
|
|
|
! Get the drive parameters, the number of sectors is bluntly written into the
|
|
! floppy disk sectors/track array.
|
|
|
|
movb ah, #0x08 ! Code for drive parameters
|
|
int 0x13 ! dl still contains drive
|
|
andb cl, #0x3F ! cl = max sector number (1-origin)
|
|
movb (di), cl ! Number of sectors per track
|
|
incb dh ! dh = 1 + max head number (0-origin)
|
|
#endif
|
|
jmp loadboot
|
|
|
|
#ifndef CDBOOT
|
|
! Floppy:
|
|
! Execute three read tests to determine the drive type. Test for each floppy
|
|
! type by reading the last sector on the first track. If it fails, try a type
|
|
! that has less sectors. Therefore we start with 1.44M (18 sectors) then 1.2M
|
|
! (15 sectors) ending with 720K/360K (both 9 sectors).
|
|
|
|
next: inc di ! Next number of sectors per track
|
|
|
|
floppy: xorb ah, ah ! Reset drive
|
|
int 0x13
|
|
|
|
movb cl, (di) ! cl = number of last sector on track
|
|
|
|
cmpb cl, #9 ! No need to do the last 720K/360K test
|
|
je success
|
|
|
|
! Try to read the last sector on track 0
|
|
|
|
mov es, lowsec(bp) ! es = vector segment (lowsec = 0)
|
|
mov bx, #BUFFER ! es:bx buffer = 0x0000:0x0600
|
|
mov ax, #0x0201 ! Read sector, #sectors = 1
|
|
xorb ch, ch ! Track 0, last sector
|
|
xorb dh, dh ! Drive dl, head 0
|
|
int 0x13
|
|
jc next ! Error, try the next floppy type
|
|
|
|
success:movb dh, #2 ! Load number of heads for multiply
|
|
#endif
|
|
|
|
loadboot:
|
|
! Load /boot from the boot device
|
|
|
|
#ifndef CDBOOT
|
|
movb al, (di) ! al = (di) = sectors per track
|
|
mulb dh ! dh = heads, ax = heads * sectors
|
|
mov secpcyl(bp), ax ! Sectors per cylinder = heads * sectors
|
|
#endif
|
|
|
|
mov ax, #BOOTSEG ! Segment to load /boot into
|
|
mov es, ax
|
|
xor bx, bx ! Load first sector at es:bx = BOOTSEG:0x0000
|
|
mov si, #LOADOFF+addresses ! Start of the boot code addresses
|
|
load:
|
|
mov ax, 1(si) ! Get next sector number: low 16 bits
|
|
movb dl, 3(si) ! Bits 16-23 for your up to 8GB partition
|
|
xorb dh, dh ! dx:ax = sector within partition
|
|
#ifndef CDBOOT
|
|
add ax, lowsec+0(bp)
|
|
adc dx, lowsec+2(bp)! dx:ax = sector within drive
|
|
cmp dx, #[1024*255*63-255]>>16 ! Near 8G limit?
|
|
jae bigdisk
|
|
div secpcyl(bp) ! 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 (di) ! 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)
|
|
movb dh, al ! dh = al = head
|
|
movb dl, device(bp) ! dl = device to read
|
|
movb al, (di) ! Sectors per track - Sector number (0-origin)
|
|
subb al, ah ! = Sectors left on this track
|
|
cmpb al, (si) ! Compare with # sectors to read
|
|
jbe read ! Cant read past the end of a cylinder?
|
|
movb al, (si) ! (si) < sectors left on this track
|
|
read: push ax ! Save al = sectors to read
|
|
movb ah, #0x02 ! Code for disk read (all registers in use now!)
|
|
int 0x13 ! Call the BIOS for a read
|
|
pop cx ! Restore al in cl
|
|
jmp rdeval
|
|
#endif
|
|
bigdisk:
|
|
movb cl, (si) ! Number of sectors to read
|
|
push si ! Save si
|
|
mov si, #LOADOFF+ext_rw ! si = extended read/write parameter packet
|
|
movb 2(si), cl ! Fill in # blocks to transfer
|
|
mov 4(si), bx ! Buffer address
|
|
mov 8(si), ax ! Starting block number = dx:ax
|
|
mov 10(si), dx
|
|
movb dl, device(bp) ! dl = device to read
|
|
movb ah, #0x42 ! Extended read
|
|
int 0x13
|
|
pop si ! Restore si to point to the addresses array
|
|
!jmp rdeval
|
|
rdeval:
|
|
jc error ! Jump on disk read error
|
|
movb al, cl ! Restore al = sectors read
|
|
addb bh, al ! bx += 2 * al * 256 (add bytes read)
|
|
addb bh, al ! es:bx = where next sector must be read
|
|
#ifdef CDBOOT
|
|
addb bh, al ! For CDs, a sector is 2048 bytes, so
|
|
addb bh, al ! do this 6 more times to get byte count.
|
|
addb bh, al
|
|
addb bh, al
|
|
addb bh, al
|
|
addb bh, al
|
|
#endif
|
|
add 1(si), ax ! Update address by sectors read
|
|
adcb 3(si), ah ! Don't forget bits 16-23 (add ah = 0)
|
|
subb (si), al ! Decrement sector count by sectors read
|
|
jnz load ! Not all sectors have been read
|
|
add si, #4 ! Next (address, count) pair
|
|
cmpb ah, (si) ! Done when no sectors to read
|
|
jnz load ! Read next chunk of /boot
|
|
|
|
done:
|
|
|
|
! Call /boot, assuming a long a.out header (48 bytes). The a.out header is
|
|
! usually short (32 bytes), but to be sure /boot has two entry points:
|
|
! One at offset 0 for the long, and one at offset 16 for the short header.
|
|
! Parameters passed in registers are:
|
|
!
|
|
! dl = Boot-device.
|
|
! es:si = Partition table entry if hard disk.
|
|
!
|
|
pop si ! Restore es:si = partition table entry
|
|
pop es ! dl is still loaded
|
|
jmpf BOOTOFF, BOOTSEG ! jmp to sec. boot (skipping header).
|
|
|
|
! Read error: print message, hang forever
|
|
error:
|
|
mov si, #LOADOFF+errno+1
|
|
prnum: movb al, ah ! Error number in ah
|
|
andb al, #0x0F ! Low 4 bits
|
|
cmpb al, #10 ! A-F?
|
|
jb digit ! 0-9!
|
|
addb al, #7 ! 'A' - ':'
|
|
digit: addb (si), al ! Modify '0' in string
|
|
dec si
|
|
movb cl, #4 ! Next 4 bits
|
|
shrb ah, cl
|
|
jnz prnum ! Again if digit > 0
|
|
|
|
mov si, #LOADOFF+rderr ! String to print
|
|
print: lodsb ! al = *si++ is char to be printed
|
|
testb al, al ! Null byte marks end
|
|
hang: jz hang ! Hang forever waiting for CTRL-ALT-DEL
|
|
movb ah, #0x0E ! Print character in teletype mode
|
|
mov bx, #0x0001 ! Page 0, foreground color
|
|
int 0x10 ! Call BIOS VIDEO_IO
|
|
jmp print
|
|
|
|
.data
|
|
rderr: .ascii "Read error "
|
|
errno: .ascii "00 \0"
|
|
errend:
|
|
|
|
! Floppy disk sectors per track for the 1.44M, 1.2M and 360K/720K types:
|
|
sectors:
|
|
.data1 18, 15, 9
|
|
|
|
! Extended read/write commands require a parameter packet.
|
|
ext_rw:
|
|
.data1 0x10 ! Length of extended r/w packet
|
|
.data1 0 ! Reserved
|
|
.data2 0 ! Blocks to transfer (to be filled in)
|
|
.data2 0 ! Buffer address offset (tbfi)
|
|
.data2 BOOTSEG ! Buffer address segment
|
|
.data4 0 ! Starting block number low 32 bits (tbfi)
|
|
.data4 0 ! Starting block number high 32 bits
|
|
|
|
.align 2
|
|
addresses:
|
|
! The space below this is for disk addresses for a 38K /boot program (worst
|
|
! case, i.e. file is completely fragmented). It should be enough.
|