Why is the efficiency of the Cyclone® V and Arria® V hard memory controller lower than expected for single port designs?

Description

The Multi-Port Front End (MPFE), used with the Hard Memory Controller for Arria® V and Cyclone® V devices, contains an arbiter that enables load balancing across multiple ports. In addition, the MPFE will always grant access to a different port after it has finished serving a port.

This behavior means that where the MPFE only receives traffic on one port, either because no other ports have pending transactions or because a single port variation is generated, the controller will implement writes in 5 clock cycles instead of 4 clock cycles. Reads are not affected.

This behavior may also be seen in multi-port MPFE configurations.

Resolution

There is no workaround for this behavior.