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80386
31
16 15
0
BREAKPOINT 0
LINEAR ADDRESS
ORO
BREAKPOINT 1 LINEAR ADDRESS
DR1
BREAKPOINT 2 LINEAR ADDRESS
DR2
BREAKPOINT 3 LINEAR ADDRESS
DR3
Intel reserved.
Do
not define.
DR4
Intel reserved.
Do
not define.
DR5
0
B
B B
o 0 o 0 o 0 o 0
o B
B B B
DR6
T
S 0 3
210
LEN
I
~
I W I
LEN
I R I w I
LEN
I R I w I
LEN
I R I w
0
o G
o 0
OG
L G L G L G L G L
DR?
333222111000
0 E E 3
322
1
100
31
16
15
0
NOTE:
~
indicates Intel reserved:
Do
not define;
SEE
SECTION 2.3.10
Figure 2-13. Debug Registers
tion breakpoints must have a
length of 1 (LENi
00).
Encoding of the LENi field
is
as
follows:
Usage
of
Least
LENi
Brealcpoint Significant Bits in
Encoding
Field Width Brea!cpoint
Address
Register
i,
(i
= 0 -
3)
00 1 byte
All
32-bits used to
specify a
single·byte
breakpoint field.
01
2 bytes A1-A31 used to
specify a
two· byte,
word·aligned
breakpoint field.
AD
in
Breakpoint Address
Register
is
not used.
10
Undefined-
do not
use
this encoding
11
4 bytes A2-A31 used to
specify a
four·byte,
dword-aligned
breakpoint
field.
AD
and A 1
in
Breakpoint
Address Register are
not used.
The LENi
field controls the size of breakpoint field i
by
controlling whether all low·order linear address
bits
in
the breakpoint address register are used to
detect the breakpoint event. Therefore,
all break·
point fields are aligned; 2·byte breakpoint fields be-
gin
on Word boundaries, and 4-byte breakpoint
fields begin
on
Dword boundaries.
29
The following
is
an
example of various size break-
point fields. Assume the breakpoint linear address
in
DR2
is
00000005H.
In
that situation, the following
illustration
indicates the region of the breakpoint
field for lengths of
1,
2,
or 4 bytes.
DR2
= 00000005H; LEN2 =
OOB
!=
31===!
==!b=k
P
t=fld2:!
=:0
!:::::::;:
DR2
= 00000005H;
31
LEN2 = 01B
I
o
I
00000008H
-
bkpt fld2
~
00000004H
I
OOOOOOOOH
L-
____
~
____
L-
____
L_
__
~
DR2 = 00000005H; LEN2 = 11B
31
I I I
0
I I
00000008H
-
bkpt fld2
--l>
00000004H
I I
OOOOOOOOH