VR4102 datasheet(219/701 Pages) NEC

219 / 701 page

CHAPTER 8 CACHE MEMORY

219

8.5 CACHE STATE TRANSITION DIAGRAMS

The following section describes the cache state diagrams for the data and instruction caches.

These state

diagrams do not cover the initial state of the system, since the initial state is system-dependent.

8.5.1 Data Cache State Transition

The following diagram illustrates the data cache state transition sequence. A load or store operation may include

one or more of the atomic read and/or write operations shown in the state diagram below, which may cause cache

state transitions.

— Read (1) indicates a read operation from memory to cache, inducing a cache state transition.

— Write (1) indicates a write operation from CPU core to cache, inducing a cache state transition.

— Read (2) indicates a read operation from cache to the CPU core, which induces no cache state transition.

— Write (2) indicates a write operation from CPU core to cache, which induces no cache state transition.

Figure 8-6. Data Cache State Diagram

CACHE op

Write (1)

CACHE op

Write-back

Read (2)

Write (2)

Read (1)

Invalid

Valid

Dirty

Valid

Clean

8.5.2 Instruction Cache State Transition

The following diagram illustrates the instruction cache state transition sequence.

— Read (1) indicates a read operation from memory to cache, inducing a cache state transition.

— Read (2) indicates a read operation from cache to the CPU core, which induces no cache state transition.

Figure 8-7. Instruction Cache State Diagram

Read (1)

CACHE op

Read (2)

Valid

Invalid

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