ARM enables custom instructions on Cortex-M

Technology News | October 9, 2019

By Peter Clarke

The capability will be available for the ARM Cortex-M33 processor in the first half of 2020 at no additional cost, and on all future Cortex-M processors.

The move is being made to address the fast-changing nature of computation and allow licensees to address such applications as artificial intelligence, security, 5G and specific IoT applications, said Thomas Ensergueix, senior director responsible for the IoT line of business at ARM. The prospect of a trillion IoT nodes connected to the internet will produce a rapidly increasing variety of use cases and workloads, ARM said.

Ensergueix, said that in time ARM expects to broaden the use of the technique beyond M-class architecture and possibly in the R-class next.

When asked if the move was a response to the custom instruction capability within the highly modular RISC-V architecture, Ensergueix did not deny it. “We are giving options to our customers. Some already design tightly coupled coprocessors and we are allowing that workload to move within the processor. It is a race and we have to raise our game. The way we are doing it is low risk for customers.”

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Ensergueix pointed out that the use of custom instructions is the extension of a trend from bus-connected processors, to closely-coupled co-processors. “The ARM architecture becomes a chassis to contain instructions,” he said. He added that the additional instructions are implemented in custom logic rather than the conventional datapath and this forms a key part of preserving the integrity of the ecosystem tools – compilers, instruction set simulators and fast models – and preventing fragmentation of software.