ARM ARM7TDMI - Page 268

Debug in Depth
B-58 Copyright © 2001, 2004 ARM Limited. All rights reserved. ARM DDI 0210C
The address comparator output of the watchpoint is used to drive the write enable for
the CHAINOUT latch. The input to the latch is the output of the data comparator from
the same watchpoint. The output of the latch drives the CHAIN input of the breakpoint
comparator. The address YYY is stored in the breakpoint register and when the CHAIN
input is asserted, the breakpoint address matches and the breakpoint triggers correctly.
B.18.2 RANGEOUT signal
The RANGEOUT signal is derived as follows:
RANGEOUT = ((({Av[31:0],Cv[4:0]} XNOR {A[31:0],C[4:0]}) OR {Am[31:0],Cm[4:0]}) == 0xFFFFFFFFF) AND
((({Dv[31:0],Cv[7:5]} XNOR {D[31:0],C[7:5]}) OR
Dm[31:0],Cm[7:5]}) == 0x7FFFFFFFF)
The RANGEOUT output of watchpoint register 1 provides the RANGE input to
watchpoint register 0. This RANGE input enables you to couple two breakpoints
together to form range breakpoints.
Selectable ranges are restricted to being powers of 2. For example, if a breakpoint is to
occur when the address is in the first 256 bytes of memory, but not in the first 32 bytes,
program the watchpoint as follows:
For Watchpoint 1:
1. Program Watchpoint 1 with an address value of
0x00000000 and an address mask
of
0x0000001F .
2. Clear the ENABLE bit.
3. Program all other Watchpoint 1 registers as normal for a breakpoint. An address
within the first 32 bytes causes the RANGE output to go HIGH but does not
trigger the breakpoint.
For Watchpoint 0:
1. Program Watchpoint 0 with an address value of
0x00000000 and an address mask
of
0x000000FF .
2. Set the ENABLE bit.
3. Program the RANGE bit to match a 0.
4. Program all other Watchpoint 0 as normal for a breakpoint.
If Watchpoint 0 matches but Watchpoint 1 does not, that is the RANGE input to
Watchpoint 0 is 0, the breakpoint is triggered.