Arm brings custom instructions to its embedded CPUs

At its annual TechCon event in San Jose, Arm today announced Custom Instructions, a new feature of its Armv8-M architecture for embedded CPUs that, as the name implies, enables its customers to write their own custom instructions to accelerate their specific use cases for embedded and IoT applications.

"We already have ways to add acceleration, but not as deep and down to the heart of the CPU. What we're giving [our customers] here is the flexibility to program your own instructions, to define your own instructions - and have them executed by the CPU," ARM senior director for its automotive and IoT business, Thomas Ensergueix, told me ahead of today's announcement.

He noted that Arm always had a continuum of options for acceleration, starting with its memory-mapped architecture for connecting GPUs and today's neural processor units over a bus. This allows the CPU and the accelerator to run in parallel, but with the bus being the bottleneck. Customers can also opt for a co-processor that's directly connected to the CPU, but today's news essentially allows Arm customers to create their own accelerated algorithms that then run directly on the CPU. That means the latency is low, but it's not running in parallel, as with the memory-mapped solution.

As Arm, argues, this setup allows for the lowest-cost (and risk) path for integrating customer workload acceleration, as there are no disruptions to the existing CPU features and still allows its customers to use the existing standard tools they are already familiar with.

For now, custom instructions will only be available to be implemented in the Arm Cortex-M33 CPUs, starting in the first half of 2020. By default, it'll also be available for all future Cortex-M processors. There are no additional costs or new licenses to buy for Arm's customers.

Ensergueix noted that as we're moving to a world with more and more connected devices, more of Arm's customers will want to optimize their processors for their often very specific use cases - and often they'll want to do so because by creating custom instructions, they can get a bit more battery life out of these devices, for example.

Arm has already lined up a number of partners to support Custom Instructions, including IAR Systems, NXP, Silicon Labs and STMicroelectronics .

"Arm's new Custom Instructions capabilities allow silicon suppliers like NXP to offer their customers a new degree of application-specific instruction optimizations to improve performance, power dissipation and static code size for new and emerging embedded applications," writes NXP's Geoff Lees, SVP and GM of Microcontrollers. "Additionally, all these improvements are enabled within the extensive Cortex-M ecosystem, so customers' existing software investments are maximized."

In related embedded news, Arm also today announced that it is setting up a governance model for Mbed OS, its open-source operating system for embedded devices that run an Arm Cortex-M chip. Mbed OS has always been open source, but the Mbed OS Partner Governance model will allow Arm's Mbed silicon partners to have more of a say in how the OS is developed through tools like a monthly Product Working Group meeting. Partners like Analog Devices, Cypress, Nuvoton, NXP, Renesas, Realtek,
Samsung and u-blox are already participating in this group.