David May wants to re-RISC the ARM - Embedded.com

David May wants to re-RISC the ARM

Professor David May, a leading computer scientist, has looked at producing an implementation of a simplified ARM instruction set architecture. He has started work on the project in the interests of teaching how processors work and the fundamentals of parallel programming.

Professor May revealed the project – based around the 30 or so most-useful ARM Thumb instructions – at the end of a lecture entitled “Heterogeneous processors: Why?” given at the Multicore Challenge one-day conference organized by Test and Verification Solutions Ltd. (TVS) recently and held in Bristol.

Professor May, of Bristol University and who is also CTO of XMOS Ltd., is still probably best known as the lead architect of the transputer, a processor designed explicitly for ease of parallel processing.

As I expected, he provided much food for thought in his talk. I was unable to attend the conference, but thanks to TVS archiving material on YouTube I have been able to experience the presentation almost as if I had been there.

In his talk Professor May pointed out that heterogeneous multiprocessing systems have been around for a long time but he also argued for keeping systems simple and, where possible, resisting the urge to use multiple architectures, in the interests of simplicity and computational and development efficiency. “One architecture means one set of programming languages and tools,” he pointed out.

The extension of that argument was that if you want heterogeneity it would be better to have it in the implementation of processor cores based on a single architecture rather than in multiple architectures, which sounds like an argument for designing CPUs, GPUs, I/O processors and radio processing units all within a single common architecture framework.

One could argue that ARM's “big-little” implementation of Cortex-A15 and Cortex-A7 processor cores falls in-line with this argument, although Professor May could not resist a little gibe at ARM asking: “Is a chip with several different ARMs heterogeneous? You could argue it is fairly heterogeneous given that it takes a 1,000-page manual to describe all the different variants.”

Professor David May of Bristol University and CTO of XMOS Ltd.

To read more, go to “The most useful 37 Thumb instructions.”

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