Abstract

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 thesis 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 thesis 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 simulationbased

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.

Key Words

System on Chip (SoC)

Core-Based Design

On Chip Communication

Network on Chip (NoC)

Packet Switched Network

Routing Algorithms

Source Routing

Junction-Based Routing

Specification and Description Language (SDL)