Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 4/01/2024
Public
Document Table of Contents

4.1.5.6. Snoop Filters

CCU uses snoop filters to reduce the system bandwidth consumed to enforce coherence by eliminating unnecessary coherency operations. On Agilex™ 5 CCU there is one snoop filter, assigned to CAIU0 caching agent.

A tag filter is a set-associative structure that tags entries by physical address and stores cache line validity and ownership information about its associated caching agents so that only the necessary coherency operations are performed on those caching agents. Each caching agent is represented by a bit that indicates whether the caching agent is a sharer and one of the caching agents, represented by a pointer field, may be designated as the owner of the cache line. A sharer caches a valid, clean, non-unique copy of data, while an owner caches a valid copy of data that may be either dirty or unique. For a coherent transaction that requires a valid copy of a cache line, only the owner is snooped, and for a coherent transaction that requires a unique copy of a cache line, the owner and each sharer are snooped.