When you generate designs with a version of the high-performance controller II (HPC II) earlier than 11.0, the merging feature is turned off by default. Burst Merging is not supported in HPC II generated by the Quartus II software versions 11.0 to 12.0. Support resumes beginning in version 12.1.
If your traffic exercises pattern that you can merge, you should turn on merging. Turning merging on may affect fMAX performance.
This issue affects all ALTMEMPHY-based designs generated with a pre-11.0 version of the HPC II architecture.
If you can merge traffic when you turn on the merging feature, there is a performance improvement.
Controllers in half-rate configuration may not see Burst Merging happen often, although the Avalon command is set to a Burst Chop (BC) size of 1 because the controller is able to process 1 Burst Chop command every clock. Burst Merging happens only when the controller temporarily stops processing commands due to Refresh or execution of row commands such as Activate/Precharge.