AN2203 Freescale Semiconductor / Motorola, AN2203 Datasheet - Page 16

• Manufacturer Part Number: AN2203
• Description: MPC7450 RISC Microprocessor Family Software Optimization Guide
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Overview of Target Microprocessors
a code performance point of view, the need for biasing the branch to be fall-through has increased to avoid
the 1- or 2-cycle fetch bubble of a taken branch.
The longer pipeline makes the MPC7450 more sensitive to branch misprediction than earlier designs.
2.3.3.9
MPC7450 Compiler Model
A good scheduling model for the MPC7450 should take into account the dispatch limitations of the three
instructions per cycle, the 16-entry CQ has completion limitation of three instructions per cycle, and the
various execution units with the latencies discussed earlier.
A full model would also incorporate the full table-driven latency/throughput/serialization specifications for
each instruction listed in Appendix A, “MPC7450 Execution Latencies.” The usage and availability of
reservation stations and rename registers should also be incorporated. Finally, attention should be given to
the issue limitations of the various issue queues—for example, it is important to note that AltiVec
instructions must be issued in-order out of the vector issue queue. This means that a few poorly scheduled
instructions can potentially stall the entire vector unit for many cycles.
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MPC7450 RISC Microprocessor Family Software Optimization Guide
MOTOROLA
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