Home / ARM / ARM vs. RISC-V


At Critical Link, we spend a lot of time thinking about processors, and for a while now, some of that thinking has been around ARM vs. RISC-V Instruction Set Architectures, or ISA’s which are basically the go-between between hardware and software. So I was very interested to come across an article by Shreyas Sharma, which was published on Wevolver last summer. Sharma’s piece provided a “comprehensive comparison” of these two key architectures, which I’ll summarize here, also offering some thoughts on how Critical Link views the debate.

Let’s set the groundwork with some brief descriptions. ARM is a proprietary ISA. Itself a member of the RISC (Reduced Instruction Set Computing) family, ARM has been around in some form since the mid-1980’s. Over time, ARM has become very prevalent when it comes to embedded systems and mobile devices. (Critical Link has developed a number of ARM-based SOM’s.) RISC-V is not exactly a newcomer, but was not commercialized until 2018. Despite its being open source/royalty free, RISC-V hasn’t gained as much traction as ARM. But adoption is rapidly accelerating and is now seen as a more head-to-head ARM competitor, with ARM-based architectures seen as more proven and reliable, while RISC-V is generally viewed as more flexible and, thus, more likely to enable innovation.

Which is not to say that ARM is inflexible. ARM has been licensed by many semiconductor companies who have used the underlying IP to create ARM processor families that have been customized for specific industries and applications. And there are an awful lot of ARM chips out there “with over 180 billion ARM chips shipped to date. Around 30 billion ARM chips are shipped every year.” (Sharma’s article doesn’t include the stats on RISC-V, but the numbers I’ve seen – which admittedly may be a bit out of date by a year or so – put the number of RISC-V processors out there at roughly ten billion.)

Some of the technical highlights of Sharma’s article – which is well worth the read – include the differentiation between the two architectures.

Among other aspects, RISC-V’s design translates into greater modularity and extensibility.

The ISA is designed to be easily extended with custom instructions and coprocessors, allowing for tailored implementations that meet specific application requirements. This flexibility is achieved through a modular design, where the base ISA can be combined with optional standard extensions, such as the M extension for integer multiplication and division, the A extension for atomic operations, and the F and D extensions for single- and double-precision floating-point arithmetic.

The focus of ARM architecture is “on power efficiency and simplicity.”

ARM processors typically implement the ARM and Thumb instruction sets, with the latter providing 16-bit compressed instructions for improved code density and energy efficiency. ARM introduced the Thumb instruction set as an optional 16-bit extension to the traditional 32-bit ARM instructions. This feature enables code size reduction while maintaining reasonable performance, making it suitable for memory-constrained devices like embedded systems.

As noted earlier, there are a number of ARM processor families that enable “specific performance and power requirements.” For high-performance apps, there’s the Cortex-A series. Cortex-R processors are used in real-time applications, while Cortex-M is optimized for energy efficiency and ease of use. So, while RISC-V may be more customizable, the different ARM processor families are to some degree “pre-customized” for specific applications and industries.

Most of the System on Modules Critical Link has brought to market include an ARM processor. These are most commonly of the A variety, for example the dual Cortex-A76 + dual Cortex-A55s that are on the MitySOM-A5E, our Intel/Altera Agilex 5 SoC based solution currently in development. Despite having significantly more processing resources than the Cyclone V SoC, the Agilex 5E will consume 50% less power – a major advantage for developers who are constantly looking for ways to make designs more efficient while also building in more advanced features.

Another of our newer families, the MitySOM-AM62A, includes a Cortex-R5F which customers use for things like managing an EtherCAT master interface, providing safety critical software operation, or real-time handling of attached peripherals.

When it comes to performance, Sharma gives the nod to ARM’s holding the advantage. He does qualify this a bit:

However, RISC-V’s modular nature and customization potential hold promise for specific use cases. The ongoing efforts of RISC-V proponents to narrow the performance gap will be a crucial factor in determining how well RISC-V can match ARM’s established performance standards in the future.

Since power efficiency is one of ARM’s core strengths, it’s no surprise that Sharma gives ARM “a palpable advantage in power efficiency” when compared with RISC-V.

Power efficiency has been a key focus of the ARM architecture since its inception, making it the preferred choice for many mobile and embedded applications. ARM processors are designed to deliver high performance with low power consumption, enabling the development of energy-efficient devices across a wide range of applications…

While RISC-V holds promise due to its customization potential, its open nature requires a more extensive investment of time and resources to fully harness its energy-saving capabilities.

Since it’s been around longer, and has such broad adoption, the ARM ecosystem is far more extensive than that of RISC-V. In Sharma’s view,

… while ARM’s extensive ecosystem offers stability, proven tools, and a wide range of hardware options, RISC-V’s open-source nature fosters collaboration, customization, and innovation.

Sharma also provides some useful discussion on the different business/licensing models for the two architectures. He also gets into use cases. RISC-V: IoT devices such as wearables and home automation systems; ARM: mobile devices, embedded systems, industrial controls, and IoT devices. He does see overlap in many areas, including deployment of both technologies in data centers.)

Sharma’s article delivers on its promise to provide “a comprehensive comparison of [RISC-V and ARM] processor architectures.” There are certainly advantages to each, and while ARM clearly dominates the industrial space – and our offerings — right now, we’re always on the lookout for opportunities to incorporate new (or maybe just new to our portfolio!) technology.


Source for image: The Tech Edvocate