Epson ARM.POWERED ARM720T - Manual (Page 170)

9: Debugging Your System
9-38 EPSON ARM720T CORE CPU MANUAL
9.22 Programming watchpoints
This section contains examples of how to program the watchpoint unit to generate breakpoints
and watchpoints. Many other ways of programming the watchpoint unit registers are possible.
For example, simple range breakpoints can be provided by setting one or more of the address
mask bits.
To make a watchpoint unit cause watchpoints (on data accesses):
1 Program its address value register with the address of the data access to be
watchpointed.
2 Program the address mask register to 0x00000000.
3 Program the data value register only if you require a data-dependent watchpoint,
that is, only if you have to match the actual data value read or written as well as
the address. If the data value is irrelevant, program the data mask register to
0xFFFFFFFF
(all bits set). Otherwise program the data mask register to
0x00000000
.
4 Program the control value register as follows:
PROT[0]
Set.
HWRITE Clear for a read.
Set for a write.
SIZE[1:0] Program with the value corresponding to the appropriate data size.
5 Program the control mask register as follows:
PROT[0]
Clear.
HWRITE Clear.
Note:
You can set this bit if both reads and writes are to be
watchpointed.
SIZE[1:0] Clear.
Note:
You can set these bits if data size accesses are to be
watchpointed.
All other bits Set.
6 If you have to make the distinction between User and non-User mode data accesses,
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.
9.23 Abort status register
Only bit 0 of this 32 bit read/write register is used. It determines whether an abort exception
entry was caused by a breakpoint, a watchpoint, or a real abort. The format is shown in
Figure 9-14.
Figure 9-14 Debug abort status register
Bit 0 is set when the ARM720T core takes a Prefetch or Data Abort as a result of a breakpoint
or watchpoint. If, on a particular instruction or data fetch, both the Debug Abort and the
external Abort signal are asserted, the external Abort takes priority, and the DbgAbt bit is not
set. Once set, DbgAbt remains set until reset by the user. The register is accessed by MRC and
MCR instructions.
DbgAbt
0
SBZ/RAZ
31:1