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Debugging Your System
5-54 Copyright © 2001 ARM Limited. All rights reserved. ARM DDI 0234B
5.21.2 Software breakpoints
To make a watchpoint unit cause software breakpoints (on instruction fetches of a
particular bit pattern):
1. Program its address mask register to
0xffffffff
(all bits set to 1) so that the
address is disregarded.
2. Program the data value register with the particular bit pattern that has been chosen
to represent a software breakpoint.
If you are programming a Thumb software breakpoint, repeat the 16-bit pattern
in both halves of the data value register. For example, if the bit pattern is
0xdfff
,
program
0xdfffdfff
. When a 16-bit instruction is fetched, EmbeddedICE-RT
compares only the valid half of the data bus against the contents of the data value
register. In this way, you can use a single watchpoint register to catch software
breakpoints on both the upper and lower halves of the data bus.
3. Program the data mask register to
0x00000000
.
4. Program the control value register with PROT[0] = 0.
5. Program the control mask register with PROT[0] = 0 and all other bits to 1.
6. If you want to make the distinction between User and non-User mode instruction
fetches, program the PROT[1] bit in the control value, and control mask registers
accordingly.
7. If required, program the DBGEXT, RANGE, and CHAIN bits in the same way.
Note
You do not have to program the address value register.
Setting the breakpoint
To set the software breakpoint:
1. Read the instruction at the desired address and store it.
2. Write the special bit pattern representing a software breakpoint at the address.
Clearing the breakpoint
To clear the software breakpoint, restore the instruction to the address.
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