A11.3 ACP performance

The ACP interface can support up to four outstanding transactions. These can be any combination of reads and writes.

The master must avoid sending more than one outstanding transaction on the same AXI ID, to prevent the second transaction stalling the interface until the first has completed. If the master requires explicit ordering between two transactions, ARM recommends that it waits for the response to the first transaction before sending the second transaction.

Writes are higher performance when they contain a full cache line of data.

If SCU cache protection is configured, writes of less than 64 bits incur an overhead of performing a read-modify-write sequence if they hit in the L2 cache.

Some L2 resources are shared between the ACP interface and the cores, therefore heavy traffic on the ACP interface might, in some cases, reduce the performance of the cores.

AXI and ACEYou can use the ARCACHE and AWCACHE signals to control whether the ACP request causes an allocation into the L2 cache if it misses.
CHITo ensure correct ordering of data beats, ACP reads that miss always allocate into the L2 cache.
Non-ConfidentialPDF file icon PDF versionARM 100241_0001_00_en
Copyright © 2016, 2017 ARM Limited or its affiliates. All rights reserved.