  This work is devoted to the study of communication subsystem of
networks-onchip (NoCs) development with an emphasis on their topologies. The
main characteristics of NoC topologies and the routing problem in NoCs with
various topologies are considered. It is proposed to use two-dimensional
circulant topologies for NoC design, since they have significantly better
characteristics than most common mesh and torus topologies, and, in contrast to
many other approaches to improving topologies, have a regular structure. The
emphasis is on using ring circulants which although in some cases have somewhat
worse characteristics than the optimal circulants, compensate by one-length
first generatrix in such graphs that greatly facilitate routing in them. The
paper considers three different approaches to routing in NoCs with ring
circulant topology: Table routing, Clockwise routing, and Adaptive routing. The
algorithms of routing are proposed, the results of synthesis of routers, based
on them, are presented, and the cost of chip resources for the implementation
of such communication subsystems in NoCs is estimated.
