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|
! This bootsector is modified by the installer to have a list of sectors at
! offset 256.
! Table format is a list of dwords. Each dword has a partition offest in
! the low 24 bits and a count in the high.
!
! Prob better to make it: HH DD MM LL rather than DD HH MM LL
! as this matches the BIOS better
!
! Note:
! Stack top is at abs location 64k.
!
! PS: This hasn't been tested much ... make that at all!
BOOTSEG = 0x07c0
LOADSEG = 0x07e0 ! Just after boot sector.
public linear
linear = 1 ! Is linear processing done ? (0 doesn't work)
public floppy
floppy = 0 *linear ! Allow for floppy drive ? (don't work)
public reloc
reloc = 1 *linear ! Auto configure of bootpart.
macro locn
if *-start>?1
fail! ?1
endif
.blkb ?1 + start-*
mend
use16
entry start
org $7b00
! temporary space
n_cyl: .blkw 1
n_secs: .blkw 1
t_drive: .blkb 1
t_sector: .blkb 1
t_secs: .blkw 1
org $7c00
start:
j code
runit:
jmpi 0,0 ! This instruction is altered by the installer
public execaddr ! Via this label.
execaddr = *-4
public bootpart
bootpart:
.data4 0x80000011
code:
if reloc
mov cx,[si+8] ! Fetch the linear address of part from DS:SI
mov dh,[si+10] ! DL is drive number
xchg dl,dh ! Into normal form.
endif
xor ax,ax
mov ds,ax
mov ss,ax
mov sp,ax
if reloc
mov [bootpart],cx
mov [bootpart+2],dx
endif
! ASSUME ds=ss= 0 (cs should also be zero)
mov ax,#LOADSEG
mov es,ax
mov si,#table
load_addrs:
cld
if linear
lodsw
mov cx,ax
add cx,[bootpart]
lodsw
mov dx,[bootpart+2]
adc dl,al
mov al,ah
else
lodsw ; XXX Broken, doesn't set AL correctly.
mov cx,ax
lodsw
mov dx,ax
lodsb
endif
test al,al
jz runit
loadem:
xor bx,bx
push ax
call cread
jc failed
pop ax
mov cl,#5
sal ax,cl
mov bx,es
add ax,bx
mov es,ax
j load_addrs
! Humm, something goes wrong, not much we can do ...
! Let`s squeak then try again
failed:
mov ax,#$0E45
mov bx,#7
int $10
pop ax
j loadem
cread:
! This function is like BIOS 1302 but it`s linear.
! It's taken, almost, intact from LILO.
! DH is drive, DL:CX is linear address, AL is count.
! ES:BX is load address, beware of DMA limitations
! All registers except AX and flags are preserved.
mov t_secs,al ! save number of sectors
lnread: push cx ! keep linear address
push dx
xchg dl,dh
if linear
if floppy
test dl,#0x80 ! Floppy is physical only.
jz lrd
endif
push bx ! BX is used as scratch
push cx ! LSW
push dx ! MSW with drive
mov ah,#8 ! get drive geometry (do not clobber ES:DI)
push es
push di
int 0x13
pop di
pop es
mov bl,dh ! BL <- #heads
pop dx ! get MSW
jnc int_ok ! error -> quit
pop cx ! discard stack contents
pop bx
pop dx
pop cx
ret ! (carry is already set)
int_ok:
mov t_drive,dl ! save drive
mov dl,dh ! linear address into DX:AX
xor dh,dh
mov bh,dh ! (clear BH too)
pop ax
push cx ! compute #cyls-1
xchg ch,cl
rol ch,1
rol ch,1
and ch,#3
mov n_cyl,cx ! save #cyls-1
pop cx
and cx,#0x3f ! CX <- #secs
mov n_secs,cx
div cx ! AX <- track, DX <- sector
inc dl
mov t_sector,dl
xor dx,dx ! divide by #heads
inc bx
div bx ! AX <- cylinder, DX <- head
mov dh,dl ! set up DX (head:drive)
mov dl,t_drive
cmp ax,n_cyl ! valid cylinder number ?
ja linerr3 ! no -> error
xchg ah,al ! build cylinder number
ror al,1
ror al,1
or al,t_sector
mov cx,ax
pop bx ! restore BX
and ax,#0x3f ! read beyond end of track ?
add ax,t_secs
cmp ax,n_secs
jna intrk ! no -> go on
mov al,n_secs ! read to end of track
sub al,t_sector
inc al
jmp lrd ! read it
intrk: mov al,t_secs ! read all sectors
endif
lrd: push ax ! save AX and BX
push bx
mov ah,#2 !
int 0x13 ! read sectors
pop bx ! restore AX and BX and the linear address
pop ax
pop dx
pop cx
if linear
jc linerr ! error -> quit
sub t_secs,al ! adjust sector count
jz lindone ! zero -> done
xor ah,ah ! increase linear address
add cx,ax
adc dh,#0
xchg ah,al ! move BX
add ah,ah
add bx,ax
jc interr ! crossing segment boundaries -> error
br lnread ! process remaining sectors
linerr3:pop bx ! pop BX and linear address
pop dx
pop cx
interr: xor ax,ax ! zero indicates internal error
else
jnc lindone
endif
linerr: stc ! error
ret
lindone:clc ! no error
ret ! done
!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
public table
table:
! .long 0x80000012
! .byte 1
! .long 0x07e00000
! .byte 0
|
