Flexible system LSI for embedded systems and its optimization techniques

In this paper, we propose a chip architecture and design techniques to simultaneously reduce both the chip cost and power consumption of system-on-a-chip (SOCs). The chip cost of SOCs consists of the design cost, the mask cost, the fabrication cost, the package cost, and the test cost. In case that the production volume of one design is large, the fabrication cost becomes relatively larger than other costs. The minimization of the fabrication cost by shrinking the chip area has been the main problem to reduce the chip cost. SOCs are not always mass-produced and their design and the mask costs are dominant. We need new design criteria and a new design methodology for SOCs whose production volume is small. Our major contribution is a proposal of a design methodology based on new criteria suitable for SOC design. In our methodology, system designers use a pre-fabricated chip, called Flexible System LSI (FlexSys) chip, which consists of a processor, memories, and other cores specific to an application domain. At the fabrication phase, the power supply for unused parts of the FlexSys chip is cut off using a few additional masks which are designed for a specific application. This leads the reduction of wasteful power consumed by circuits which do not essentially contribute to the computation of the application. Since the basic die of the FlexSys is fabricated as a general purpose product, we can reduce the cost of the dies drastically. Experimental results show that about 30% power reduction can be achieved without performance loss by reducing the wasteful power consumption.