14.2.5. Performance impact

In an error-free system, the major performance impact is the cost of the read-modify-write scheme for non-full stores in the data side. If a store buffer slot does not contain at least a full 32-bit word, it must read the word to be able to compute the check bits. This can occur because software only writes to an area of memory with byte or halfword store instructions. The data can then be written in the RAM. This additional read can have a negative impact on performance because it prevents the slot from being used for another write.

The buffering and outstanding capabilities of the memory system mask part of the additional read, and it is negligible for most codes. However, Arm recommends that you use as few cacheable STRB and STRH instructions as possible to reduce the performance impact.

Note

There might be a frequency impact because XOR trees are added on the data returned from the RAMs.

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