How to Design an ISA

The article discusses the process of designing an Instruction Set Architecture (ISA), particularly in the context of the increasing popularity of RISC-V. The author, David Chisnall, shares insights gained from projects involving ISA extensions and clean-slate ISAs for various processors. He emphasizes the importance of understanding what makes a good ISA, highlighting its role as a communication bridge between compilers and microarchitecture. The article delves into the significance of considering different source languages and microarchitectures when designing an ISA, pointing out the challenges of creating a one-size-fits-all solution. Additionally, it touches on the impact of a stable ISA as a business consideration and the interplay between ISA design and microarchitecture in achieving optimal performance. The author also addresses the misconception that ISA is less critical than microarchitecture, stressing the importance of a well-designed ISA in enabling efficient microarchitectural optimizations. Overall, the article provides a comprehensive overview of key considerations and complexities involved in designing an effective ISA for diverse computing environments.