Visible to Intel only — GUID: qtf1481129283654
Ixiasoft
Visible to Intel only — GUID: qtf1481129283654
Ixiasoft
4.5.2.1. Coherency Directory
The cache coherency unit uses a directory-based coherency protocol. The CCU has a memory structure that tracks the state of the L2 cache lines.
The coherency directory stores cache line addresses and state information about each address. The directory does not store cache line data. It is not a cache. The coherency directory only contains address and state information that other master agents snoop when making coherent accesses. The directory acts as a snoop-filter and assists the cache coherency controller in locally determining the state of a cache line without sending snoops to the L2 cache.
The directory-based protocol provides lower latency accesses, reduced network bandwidth, reduced snoop traffic for the Cortex* -A53 MPCore, and higher peak bandwidth of the system.
When the Cortex* -A53 MPCore replaces a cache line, it sends an evict request to the coherency directory for any clean lines it is dropping. The directory no longer tracks those addresses after the eviction request completes.