NEC Network Controller uPD98502 - Manual (Page 173)

CHAPTER 2 V R 4120A
Preliminary User’s Manual S15543EJ1V0UM 173
2.7.5 Cache state transition diagrams
The following section describes the cache state diagrams for the data and instruction cache lines. These state
diagrams do not cover the initial state of the system, since the initial state is system-dependent.
2.7.5.1 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 write operations shown in the state diagram below, which may cause cache state
transitions.
— Read (1) indicates a read operation from main 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.
— Write (1) indicates a write operation from CPU core to cache, inducing a cache state transition.
— Write (2) indicates a write operation from CPU core to cache, which induces no cache state transition.
Figure 2-70. Data Cache State Diagram
CACHE op CACHE op
Write (1)
Write (1)
CACHE op
Write-back
Read (2)
Read (2)
Write (2)
Read (1)
Invalid
Valid
Dirty
Valid
Clean
2.7.5.2 Instruction cache state transition
The following diagram illustrates the instruction cache state transition sequence.
Read (1) indicates a read operation from main 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 2-71. Instruction Cache State Diagram
Read (1)
CACHE op
Read (2)
Valid Invalid