Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public

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4.1. Cache Coherency Unit (CCU)

The Agilex™ 5 hard processor system (HPS) cache coherency unit (CCU) ensures consistency of shared data. The CCU hides the presence of Arm DynamIQ Shared Unit (DSU) caches from software by monitoring the state and location of shared data to ensure all requestors maintain a consistent view of shared data.

Dedicated initiator peripherals in the HPS and those built in FPGA logic access coherent memory through the CCU. Cacheable transactions from the system interconnect are also routed to the CCU.

Only the Arm DSU subsystem supports full coherency. Other transaction initiators such as the F2H bridge, Ethernet/TSN, DMA, and USB interfaces support I/O coherency. I/O coherent requestors only have the capability to snoop processor caches as they do not have their own local caches. I/O coherency, also called one-way coherency, allows HPS peripherals and FPGA initiators to see the same coherent view of system memory as the DSU subsystem.

The CCU also contains error protection logic and logic for optimal performance during coherent accesses. The CCU enables both coherent and non-coherent accesses.