
Debug Support
8-42
Copyright 1999, 2000 ARM Limited. All rights reserved.
ARM DDI 0144B
The control register bits have the functions for data comparison shown in Table 8-11 on
page 8-42.
Bit 3 programmed to 0
If bit 3 of the control register is programmed to 0, the comparators examine the
instruction address, instruction data, and instruction control buses. Bits [1:0] of the
mask register must be set to
don
’
t care
(programmed to 11). The format of the register
in this case is as shown in Figure 8-11 on page 8-43.
Table 8-11 Watchpoint control register for data comparison
Bit
Function
DnRW
Compares with the data not read/write signal from the core to detect the
direction of the data bus activity.
nRW
is 0 for a read, and 1 for a write.
DMAS[1:0]
Compares with the
DMAS[1:0]
signal from the core to detect the size of the
data bus activity.
DnTRANS
Compares with the data not translate signal from the core to determine
between a User mode (
DnTRANS
= 0) data transfer, and a privileged mode
(
DnTRANS
= 1) transfer.
EXTERN
Is an external input into the EmbeddedICE unit that allows the watchpoint to
be dependent on some external condition. The
EXTERN
input for watchpoint
0 is labeled
EXTERN0
, and the
EXTERN
input for watchpoint 1 is labeled
EXTERN1
.
CHAIN
Can be connected to the
CHAIN
output of another watchpoint to implement,
for example, debugger requests of the form
breakpoint on address YYY only
when in process XXX
.
In the ARM940T EmbeddedICE unit, the
CHAINOUT
output of watchpoint
1 is connected to the
CHAIN
input of watchpoint 0. The
CHAINOUT
output
is derived from a latch. The address/control field comparator drives the write
enable for the latch and the input to the latch is the value of the data field
comparator. The
CHAINOUT
latch is cleared when the control value register
is written or when
nTRST
is LOW.
RANGE
Can be connected to the
RANGE
output of another watchpoint register. In the
ARM940T EmbeddedICE unit, the
RANGEOUT
output of watchpoint 1 is
connected to the
RANGE
input of watchpoint 0. This allows two watchpoints
to be coupled for detecting conditions that occur simultaneously, for example,
for range-checking.
ENABLE
If a watchpoint match occurs, the
IBREAKPT
or
DBREAKPT
signal is only
asserted when the ENABLE bit is set. This bit only exists in the value register.
It cannot be masked.