Development Capabilities and Interface
MOTOROLA
MPC823 USER’S MANUAL
20-9
DEVELOPMENT
20
CAPABILITIES
&
INTERFACE
In general, breakpoints are recognized in the core only when the MSRRI bit is set, which
guarantees machine restartability after a breakpoint. In this working mode, breakpoints are
masked. There are times when it is preferable to enable breakpoints even when the MSRRI
bit is clear, even though there is a risk of causing a nonrestartable machine state. In
programmable nonmasked mode, an external development system can choose to assert a
nonmaskable external breakpoint. Watchpoints are not masked and are always reported on
the external pins, regardless of the value of the MSRRI bit. The counters, although they are
counting watchpoints, are part of the internal breakpoints logic and are not decremented
when the core is in masked mode and the MSRRI bit is clear.
Internal watchpoints are generated when a user-programmable set of conditions are met.
Internal breakpoints can be programmed to be generated either when one of the internal
watchpoints is asserted or after an internal watchpoint is asserted for user-programmable
times. Programming a certain internal watchpoint to generate an internal breakpoint can be
done either in the software, by setting the corresponding software trap enable bit, or on-the-
fly using the serial interface of the development port to set the corresponding trap enable bit.
External breakpoints can be generated by any of the system peripherals, including those
found on or outside the MPC823 or those found by an external development system.
Peripherals on the external bus use the serial interface of the development port to assert an
external breakpoint.
20.3.1 Internal Watchpoints and Breakpoints
Internal watchpoints and breakpoints are used in software debugging and the sources are
The PowerPC Core. Watchpoints do not stop your code from executing, but they indicate
when you have passed a certain testing point. Breakpoints are actually the points at which
execution is stopped. For more information on external breakpoint support, refer to
watchpoint support is based on:
Eight comparators that compare information on instruction and load/store cycles
Two counters
Two AND-OR logic structures
The comparators perform a comparison on the instruction address (I-address), the load/
store address (L-address), and the load/store data (L-data). The comparators can detect the
following conditions:
Equal to
Not equal to
Greater than
Less than
Greater-than-or-equal-to and less-than-or-equal-to are easily obtained from these four