1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
|
; BOOT - IBM hard disk boot record 6/8/82
;
;
; This is the standard boot record that will be shipped on all hard disks. It contains:
;
; 1. Code to load (and give control to) the boot record for 1 of 4 possible
; operating systems.
;
; 2. A partition table at the end of the boot record, followed by the required signature.
;
;
_data segment public
assume cs:_data,ds:_data
org 600h
cli ;no interrupts for now
xor ax,ax
mov ss,ax
mov sp,7c00h ;new stack at 0:7c00
mov si,sp ;where this boot record starts - 0:7c00
push ax
pop es ;seg regs the same
push ax
pop ds
sti ;interrupts ok now
cld
mov di,0600h ;where to relocate this boot record to
mov cx,100h
repnz movsw ;relocate to 0:0600
; jmp entry2
db 0eah
dw $+4,0
entry2:
mov si,offset tab ;partition table
mov bl,4 ;number of table entries
next:
cmp byte ptr[si],80h ;is this a bootable entry?
je boot ;yes
cmp byte ptr[si],0 ;no, is boot indicator zero?
jne bad ;no, it must be x"00" or x"80" to be valid
add si,16 ;yes, go to next entry
dec bl
jnz next
int 18h ;no bootable entries - go to rom basic
boot:
mov dx,[si] ;head and drive to boot from
mov cx,[si+2] ;cyl, sector to boot from
mov bp,si ;save table entry address to pass to partition boot record
next1:
add si,16 ;next table entry
dec bl ;# entries left
jz tabok ;all entries look ok
cmp byte ptr[si],0 ;all remaining entries should begin with zero
je next1 ;this one is ok
bad:
mov si,offset m1 ;oops - found a non-zero entry - the table is bad
msg:
lodsb ;get a message character
cmp al,0
je hold
push si
mov bx,7
mov ah,14
int 10h ;and display it
pop si
jmp msg ;do the entire message
;
hold: jmp hold ;spin here - nothing more to do
tabok:
mov di,5 ;retry count
rdboot:
mov bx,7c00h ;where to read system boot record
mov ax,0201h ;read 1 sector
push di
int 13h ;get the boot record
pop di
jnc goboot ;successful - now give it control
xor ax,ax ;had an error, so
int 13h ;recalibrate
dec di ;reduce retry count
jnz rdboot ;if retry count above zero, go retry
mov si,offset m2 ;all retries done - permanent error - point to message,
jmp msg ;go display message and loop
goboot:
mov si,offset m3 ;prepare for invalid boot record
mov di,07dfeh
cmp word ptr [di],0aa55h ;does the boot record have the
; required signature?
jne msg ;no, display invalid system boot record message
mov si,bp ;yes, pass partition table entry address
db 0eah
dw 7c00h,0
include fdisk5.cl1
org 7beh
tab: ;partition table
dw 0,0 ;partition 1 begin
dw 0,0 ;partition 1 end
dw 0,0 ;partition 1 relative sector (low, high parts)
dw 0,0 ;partition 1 # of sectors (low, high parts)
dw 0,0 ;partition 2 begin
dw 0,0 ;partition 2 end
dw 0,0 ;partition 2 relative sector
dw 0,0 ;partition 2 # of sectors
dw 0,0 ;partition 3 begin
dw 0,0 ;partition 3 end
dw 0,0 ;partition 3 relative sector
dw 0,0 ;partition 3 # of sectors
dw 0,0 ;partition 4 begin
dw 0,0 ;partition 4 end
dw 0,0 ;partition 4 relative sector
dw 0,0 ;partition 4 # of sectors
signa db 55h,0aah ;signature
_data ends
end
|
