The part of TOPAZ is simple, you only have to edit sgml files and
configure the network you want to simulate. Take a look at Router3D,
Network3D and Simula3D to figure out how to do this.
On the other side, there is a problem with component mapping in
gem5. If I am not wrong, currently only very simple mappings are
supported (mesh-style, 1 cpu per router, 1 l2 bank per router). If
you are interested in full custom mappings, you will need to recover
this feature, that was available in gems. Gems ruby was much more
flexible in terms of component mapping, because you could define
your mapping in a file (directly assign each component to the router
desired).
This has been a highly demmanded feature, if ant TOPAZ user has done
this job (back to file-specified mapping) or pretends to do it, it
would be nice to share his/her work with the rest of users...
Regards.