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! The master boot sector will have setup a stack,
! this is normally at 0:7c00 down.
! DS, SS, CS and ES will all have value 0 so the execution address is 0:7c00
! On entry the register SI will be pointer to the partition entry that
! this sector was loaded from, DL is the drive.
! Also if it's a standard Master boot DH will be the head, CX will be the
! sector and cylinder, BX=7C00, AX=1, DI=7DFE, BP=SI. There's a reasonable
! chance that this isn't true though.
! The Master boot itself will have been loaded and run at $07c00
! The BIOS must have setup a stack because interrupts are enabled
! Little else can be assumed because DOS doesn`t assume anything either
! Lowest available is $0500, MSDOS appears to use $0600 ... I wonder why?
ORGADDR=$0500
org ORGADDR
sysboot_start:
cli ! Assume _nothing_!
cld
mov bx,#$7C00 ! Pointer to start of BB.
xor ax,ax ! Segs all to zero
mov ds,ax
mov es,ax
mov ss,ax
mov sp,bx ! SP Just below BB
mov cx,#$100 ! Move 256 words
mov si,bx ! From default BB
mov di,#ORGADDR ! To the correct address.
rep
movsw
jmpi cont,#0 ! Set CS:IP correct.
cont:
sti ! Let the interrupts back in.
! This is where the code will be overlaid, the default is a hang
public codestart
codestart:
j codestart
! Partition table
public bootblock_magic
.blkb sysboot_start+0x1B6-*
table_start:
.blkb 2 ! Dirty bits
.blkb 4 ! Volume Serial Number
.blkb 2 ! Possible Magic number
.blkb sysboot_start+0x1BE-*
partition_1:
.blkb 8 ! IN,SH,SS,ST,OS,EH,ES,ET
.blkw 2 ! Linear position (0 based)
.blkw 2 ! Linear length
.blkb sysboot_start+0x1CE-*
partition_2:
.blkb 8 ! IN,SH,SS,ST,OS,EH,ES,ET
.blkw 2 ! Linear position (0 based)
.blkw 2 ! Linear length
.blkb sysboot_start+0x1DE-*
partition_3:
.blkb 8 ! IN,SH,SS,ST,OS,EH,ES,ET
.blkw 2 ! Linear position (0 based)
.blkw 2 ! Linear length
.blkb sysboot_start+0x1EE-*
partition_4:
.blkb 8 ! IN,SH,SS,ST,OS,EH,ES,ET
.blkw 2 ! Linear position (0 based)
.blkw 2 ! Linear length
.blkb sysboot_start+0x1FE-*
bootblock_magic:
.blkb 2
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