Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 8/28/2023
Public
Document Table of Contents

10.3.14.2. Implementation Details

When the processor writes to any coherent memory location, the SCU ensures that the relevant data is coherent (updated, tagged or invalidated). Similarly, the SCU monitors read operations from a coherent memory location. If the required data is already stored within the other processor’s L1 cache, the data is returned directly to the requesting processor. If the data is not in L1 cache, the SCU issues a read to the L2 cache. If the data is not in the L2 cache memory, the read is finally forwarded to main memory. The primary goal is to maximize overall memory performance and minimize power consumption.

The SCU maintains bidirectional coherency between the L1 data caches belonging to the processors. When one processor performs a cacheable write, if the same location is cached in the other L1 cache, the SCU updates it.

Non‑coherent data passes through as a standard read or write operation.

The SCU also arbitrates between the Cortex*-A9 processors if both attempt simultaneous access to the L2 cache, and manages accesses from the ACP.

In rare circumstances, when the aggregate memory throughput requested by two cores exceeds the memory subsystem capacity and the Acceleration Coherency Port (ACP) is not being used, you may observe that the SCU master arbitration fairness is reduced. This reduction occurs because unused ACP arbitration shares are reassigned to CPU0, resulting in CPU0 gaining twice the memory bandwidth of CPU1. If your application requires a balanced throughput between CPU0 and CPU1, you must design the code that runs on CPU0 so that it prevents CPU0 from using more than 50% of the available memory bandwidth.