Runtime Adaptive Extensible Embedded Processors - A Survey

Current generation embedded applications demand the computation engine to offer high performance similar to custom hardware circuits while preserving the flexibility of software solutions. Customizable and extensible embedded processors, where the processor core can be enhanced with application-specific instructions, provide a potential solution to this conflicting requirements of performance and flexibility. However, due to the limited area available for implementation of custom instructions in the datapath of the processor core, we may not be able to exploit all custom instruction enhancements of an application. Moreover, a static extensible processor is fundamentally at odds with highly dynamic applications where the custom instructions requirements vary substantially at runtime. In this context, a runtime adaptive extensible processor that can quickly morph its custom instructions and the corresponding custom functional units at runtime depending on workload characteristics is a promising solution. In this article, we provide a detailed survey of the contemporary architectures that offer such dynamic instruction-set support and discuss compiler and/or runtime techniques to exploit such architectures.