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Development Support
18-20
MPC801 USER’S MANUAL
MOTOROLA
18
NOTE
When programmed to count instruction watchpoints, the last
instruction that decrements the counter to zero is treated like any
other instruction breakpoint in the sense that it is not executed
before the machine branches to the breakpoint exception
routine. As a side effect of this behavior, the value of the counter
inside the breakpoint exception routine equals 1 and not zero.
When programmed to count load/store watchpoints, the last
instruction that decrements the counter to zero is treated like any
other load/store breakpoint in the sense that it is executed
before the machine branches to the breakpoint exception
routine. Therefore, the value of the counter inside the breakpoint
exception routine equals zero.
18.2.2.4 TRAP ENABLE PROGRAMMING.
The trap enable bits can be programmed by
regular software (only if MSR
PR
=0) using the
mtspr
instruction or on-the-fly using the
special development port interface. For more information, refer to
Section 18.3.3.3
Development Port Serial Communications
. The value used by the breakpoint generation
logic is the bit-wise OR of the software trap enable bits written using the
mtspr
instruction
and the development port trap enable bits that are serially shifted using the development
port. The software trap enable bits and development port trap enable bits can be read from
the ICTRL and LCTRL2 registers using the
mtspr
instruction. For exact bit placement, refer
to Tables 18-18 and 18-20.
18.3 DEVELOPMENT SYSTEM INTERFACE
When debugging an existing system it is sometimes helpful to be able to do so without
making any changes. Although, in some cases it is not helpful and may even make it
impossible to add load to the lines connected to the existing system. The development
system interface of the core supports this configuration.
The development system interface of the core uses the development port, which is a
dedicated serial port that does not need any of the regular system interfaces. System activity
can be controlled from the development port when the core is in debug mode. The
development port is a relatively inexpensive interface that allows the development system
to operate in a lower frequency than the core’s frequency. It is also possible to debug the
core using monitor debugger software. For more information, refer to
Section 18.4 The
Software Monitor Debugger
.
In debug mode, the core fetches all instructions from the development port. Data can be
read from or written to the development port. This allows memory and registers to be read
and modified by a development tool or emulator connected to the development port. For
protection purposes two possible working modes are defined—debug mode enable and
debug mode disable. These working modes are only selected during reset. For details, refer
to
Section 18.1.1.6 Benefits of Compression
.