
MOTOROLA
Chapter 23. Development Support
23-9
Watchpoints and Breakpoints Support
Internal watchpoints are generated when a user programmable set of conditions are met.
Internal breakpoints can be programmed to be generated either as an immediate result of
the assertion of one of the internal watchpoints, or after an internal watchpoint is asserted
for a user programmable times. Programming a certain internal watchpoint to generate an
internal breakpoint can be done either in software, by setting the corresponding software
trap enable bit, or on the fly using the serial interface implemented in the development port
to set the corresponding development port trap enable bit.
External breakpoints can be generated by any of the peripherals of the system, including
those found on the MPC561/MPC563 or externally, and also by an external development
system. Peripherals found on the external bus use the serial interface of the development
port to assert the external breakpoint.
In the RCPU, as in other RISC processors, saving/restoring machine state on the stack
during exception handling, is done mostly in software. When the software is in the middle
of saving/restoring machine state, MSR[RI] is cleared. Exceptions that occur and that are
handled by the RCPU when MSR[RI] is clear result in a non-restartable machine state. For
In general, breakpoints are recognized in the RCPU is only when MSR[RI] is set, which
guarantees machine restartability after a breakpoint. In this working mode breakpoints are
said to be masked. There are cases when it is desired to enable breakpoints even when
MSR[RI] is clear, with the possible risk of causing a non-restartable machine state.
Therefore internal breakpoints have also a programmable non-masked mode, and an
external development system can also choose to assert a non-maskable external breakpoint.
Watchpoints are not masked and therefore always reported on the external pins, regardless
of the value of MSR[RI]. The counters, although counting watchpoints, are part of the
internal breakpoints logic and therefore are not decremented when the RCPU is operating
in the masked mode and MSR[RI] is clear.
Figure 23-1 shows the watchpoint and breakpoint support of the RCPU.