Hi,
What I understood that you have two questions (correct me if I am wrong). First the memcpy works fine with all addresses but the 0XF00, plus you want to keep the memcpy moving data without interruption.
For the first question I will try to replicate this issue on a board I have and see why this happens.
For the second, I advise you to use the MSGDMA or any DMA IP (MM to MM). This will solve your problems and give the targeted results.
Here is a design example of the MSGDMA with a video link show you how to use it.
Design reference:
https://fpgacloud.intel.com/devstore/platform/17.0.0/Standard/multi-core-nios-ii-processors-reference-design-based-on-arria-10-soc-development-board/
Videos:
https://www.youtube.com/watch?v=GTKLU2UR3bA
https://www.youtube.com/watch?v=DUNAemGhUTE
Regards,