Interconnections and interrupts between nios processors

It all depends on the performance you are after on how you would implement this. You could use one single memory for all your processors and the arbiter handle who has access when. This would of course be a lower performance solution. The other is the you have a dedicated dual port memory between each of the processor that needs to communicate. This will cost more in resources, but have much higher performance since your have no data contention.

Also, a factor in this is the packet size that you desire. If it is large you might have to go more on the first method. If it is smaller packets you can easier do the dual port way. You can also do a hybrid method.

On the interrupt controller you would need one interrupt for each processor and a slave port that processor A can write to to cause an interrupt for another processor.