Using a Soft Core in a SoC Design: Experiences with picoJava

60 0740-7475/00/$10.00 © 2000 IEEE IEEE Design & Test of Computers Major technologic and economic factors are driving a revolution in computer and communication system design. Networking applications like network processors, routers on chips and home gateways, portable products like wireless telephones and internet appliances, multimedia products like set-top boxes, and embedded controllers in automobiles, printers, and hard disk drives have generated a strong demand for hardware-software systems. Simultaneously, deep submicron technologies enable placement of complex systems on single chips. Giga-scale systems with millions of gates necessitate efficient design reuse to shorten the design productivity gap using predesigned intellectual property (IP) cores. This is leading to the emergence of IP core-based hardware-software system-on-chips (SoC) as a new paradigm in electronic system design. Three types of IP cores exist, providing different optimization levels and flexibility of reuse.1 A hard core, consisting of hard layouts, is the most optimized, but offers little flexibility in terms of changing the hardware features of the core itself. Most general-purpose processor and digital signal processing (DSP) processor cores available and used today, like the cores from ARM, LSI Logic, Motorola, and IBM, are hard cores. On the other hand, a soft core is a functional description of an IP, and the soft IP specification can be both simulated and synthesized. A soft IP allows flexibility in retargeting the IP specification to better fit the core user’s needs. For example, a soft processor core allows the core user to reconfigure the features of the processor, such as its instruction set, caches, communication mechanisms, and interrupt mechanisms to make the processor core more suitable for a particular SoC application. However, as opposed to a hard core user, a soft core user (the SoC integrator) must synthesize, optimize, validate, and develop tests for the soft core before integrating it in the SoC being designed. Firm cores try to balance the optimization and fast reuse potential of hard cores and the flexibility and reconfigurability of soft cores. Firm cores are typically delivered after certain Using a Soft Core in a SoC Design: Experiences with picoJava