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MOTOROLA
MPC801 USER’S MANUAL
18-1
18
SECTION 18
DEVELOPMENT SUPPORT
Emulators require a level of control and observation that are in sharp contrast to the trend
of modern microcomputers and microprocessors in which many bus cycles are directed to
internal resources and are not externally visible. The same is true for bus analyzers. To
enhance support for development tools, some of the development support functions are
implemented in the silicon. The following features allow you to efficiently debug systems
based on the MPC801.
Program flow tracking
Internal watchpoint and breakpoint generation
Emulation systems that control core (debug mode) activity
18.1 PROGRAM FLOW TRACKING
The MPC801 provides many options for tracking program flows that impact performance in
varying degrees. The information provided while tracking code flow can be compressed and
captured externally and then parsed by a post-processing program using the
microarchitecture defined here. The program instruction flow is visible on the external bus
when the MPC801 is programmed to operate in serialized mode and show all fetch cycles
on the external bus. When working in this mode, although tracking of the program instruction
flow is simpler, the performance of the MPC801 is much lower than when working in regular
mode. For more details about programming the core to operate in this mode, see
Table 18-18.
The MPC801 implements a prefetch queue combined with parallel, out of order, and
pipelined execution. These features, plus the fact that most fetch cycles are performed
internally from the instruction cache, increases performance but makes it very difficult to
provide real program trace. Instructions progress inside the core from fetch to retirement. An
instruction retires from the machine only after it and all preceding instructions finish
executing with no exception. Therefore, only retired instructions can be considered
a
rchitecturally executed.