Cyclone V SoC AHB BUS

I googled "AXI to AHB" and found a lot of solutions, here is one from OpenCores.org: http://opencores.org/project,robust_axi2ahb

The NOC that Qsys builds uses an archeticture resembling this:

Slave IP <-- translator <-- agent <-- limiter <-- switch <-- limiter <-- agent <-- translator <-- Master IP

If you instantiate just the agent by itself you might be missing pieces of what you need. Are you trying to integrate a bunch of AHB based IP or just one? If it's just one then throwing an AXI to AHB wrapper around the IP should be fairly straight forward. If you have many IP then exporting an AXI interface to the top and handling the adaptation outside of the system might be appropriate. Even if you have multiple AHB IP to integrate, putting wrappers around them to adapt them over to AXI might be the better approach because then you don't have to worry about implementing connectivity between the IP yourself.

To answer your last question the heart of the NoC is generic and doesn't care about the protocol. It's the translators and agents that are protocol aware so there is a pair of those cores for Avalon-MM, AMBA AXI, AMBA APB. So in the case of an AXI master connecting to APB slave it's connected through AXI aware fabric cores on one side and APB aware fabric cores on the other. If you add Avalon-MM into the mix the same thing occurs. As long as your IP has a supported interface the tools take it from there and handle the fabric integration for you and that's why I'm suggeting wrapping your IP with AHB to AXI conversion logic so that you can take care of the interface and let the tools handle the rest.