To support communication among hundreds of cores on a chip, on-chip communication must be well organized. In the embedded systems using such a chip, the communication patterns can be profiled and routing can be well planned off-line.
Source routing, with many advantages over distributed routing, will be very suitable in such contexts. However, source routing has one serious drawback of overhead for storing the path information in header of every packet. This disadvantage becomes worse as the size of the network grows.
In this study we propose a technique, called Junction Based Routing (JBR), to remove this limitation. In the proposed technique, path information for only a few hops is stored in the packet header. With this information, either the packet reaches the destination, or reaches a junction from where the path information for on-ward path is picked up.
There are many interesting issues related to this approach. Two important issues related to JBR, namely, number and position of junctions and path computation for efficient deadlock free routing are discussed and solved in this work. Increase in path length by using the minimum number of junctions, link load distribution while computing paths, path encoding for JBR and packet format in JBR are also discussed.
A few tools have been developed in MATLAB to analyze the various aspects of JBR. A simulator has been also developed to evaluate the performance of JBR with simple source routing. Outline of the architecture for a junction is also proposed.
The results of simulation-based experiments show that the performance of JBR is similar to source routing. JBR is compared with source routing and the simulation based results show that latency does not increase so much using junctions.
Throughput also does not level off significantly. Header flit in JBR can carry payload data and this improves the performance of JBR in terms of throughput and latency compared to source routing which needs to store large path information. We observe improvement in throughput as compared to basic source routing when payload is very small.
Source: Jönköping University
Author: Badri, Shabnam