If the Enable Memory-Mapped Configuration and Status Register (MMR) Interface option is turned ON under the Controller tab of the Arria® 10 DDR4 IP Parameter Editor, you may see the MMR signal (mmr_slave_readdatavalid_0) toggling even though there is no user read request.
Device Family: Intel® Arria® 10
Last Modified: May 30, 2017
Version Found: v16.1 Update 2
Bug ID: FB: 452373 (MODIFIED RTL IS AVAILABLE PRIOR TO 17.1 FIX);
IP: Arria 10 External Memory Interfaces
This problem is scheduled to be fixed in a future release of the Quartus® Prime software.