Computer System Designs: System-on-Chip

5

Interconnect

5.1 INTRODUCTION

SOC designs usually involve the integration of intellectual property (IP) cores, each separately designed and verified. System integrators can maximize the reuse of design to reduce costs and to lower risks. Frequently the most important issue confronting an SOC integrator is the method by which the IP cores are connected together.

SOC interconnect alternatives extend well beyond conventional computer buses. We first provide an overview of SOC interconnect architectures: bus and network-on-chip (NOC). Bus architectures developed specifically for SOC designs are described and compared. There are many switch-based alternatives to bus-based interconnects. We will not consider ad hoc or fully customized switching interconnects that are not intended for use with a variety of IP cores. Switch-based interconnects as used in SOC interconnects are referred to as NOC technology.

An NOC usually includes an interface level of abstraction, hiding the underlying physical interconnects from the designer. We follow current SOC usage and refer to interconnect as a bus or as an NOC implemented by a switch. In the NOC the switch can be a crossbar, a directly linked interconnect, or a multistage switching network.

There is a great deal of bus and computer interconnect literature. The units being connected are sometimes referred to as agents (in buses) or nodes (in the general interconnect literature); we simply use the term units. Since current SOC interconnects usually ...