Chapter 1. Overview
1-9
MPC7400 Microprocessor Features
D 4-state (MESI) similar to the MPC604
D 5-state (MERSI), where the new R state allows shared intervention
Load/store with reservation instruction pair for atomic memory references,
semaphores, and other multiprocessor operations
Power and thermal management
Three static modes, doze, nap, and sleep, progressively reduce power
dissipation:
D DozeAll the functional units are disabled except for the time
base/decrementer registers and the bus snooping logic.
D NapThe nap mode further reduces power consumption by disabling bus
snooping, leaving only the time base register and the PLL in a powered state.
D SleepAll internal functional units are disabled, after which external system
logic may disable the PLL and SYSCLK.
Thermal management facility provides software-controllable thermal
management. Thermal management is performed through the use of three
supervisor-level registers and an MPC7400-speciTc thermal management
exception.
Instruction cache throttling provides control of instruction fetching to limit
power consumption.
Performance monitor can be used to help debug system designs and improve
software efTciency.
In-system testability and debugging features through JTAG boundary-scan
capability
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1.2.2 Instruction Flow
As shown in Figure 1-1, the MPC7400 instruction unit provides centralized control of
instruction ow to the execution units. The instruction unit contains a sequential fetcher,
six-entry instruction queue (IQ), dispatch unit, and BPU. It determines the address of the
next instruction to be fetched based on information from the sequential fetcher and from
the BPU.
See Chapter 6, òInstruction Timing,ó for a detailed discussion of instruction timing.
The sequential fetcher loads instructions from the instruction cache into the instruction
queue. The BPU extracts branch instructions from the sequential fetcher. Branch
instructions that cannot be resolved immediately are predicted using either the
MPC7400-speciTc dynamic branch prediction or the architecture-deTned static branch
prediction.