31-03-2021 | By Robin Mitchell

RISC-V is a new open-source instruction set architecture (ISA) that is gaining traction as an alternative to ARM. It is designed to be more flexible and modular than traditional ISAs, and it is already being used in various applications, including microcontrollers, embedded systems, and data centres. While ARM is currently the dominant player in the market, RISC-V has the potential to become a major contender in the future due to its open-source nature and its ability to be easily customised to meet specific requirements. What are the major differences between ARM and RISC-V, and will one win over the other?

An Emerging Processor Type

When discussing processors, the instruction set architecture (ISA) is an essential factor to consider. Programs developed by software engineers can only operate on specific ISAs unless the code is written using an interpreted language that is cross-platform (such as Python or Java).

While there are many ISAs available to designers, most of these are restricted to custom architectures for microcontrollers. In terms of large processing systems, such as desktop PCs and smartphones, only two are widely available: x86/x64 and ARM.

The x86/x64 architecture, developed by Intel, has been the industry standard since the 1970s. The ARM architecture, on the other hand, was developed in the late 1980s for use on smaller systems. The key difference between the two is that x86/x64 is a complex instruction set (CISC) with many advanced features, while ARM is a reduced instruction set (RISC) with only a handful of instructions by comparison.

RISC architecture requires more clock cycles to complete the same instruction as CISC but can do so more efficiently, making it ideal for mobile applications. However, x86/x64 remains the dominant architecture in heavy processing markets. But ARM may face serious competition from a new processor architecture, RISC-V, which is open-source, customisable and does not require any royalties or licenses.


What is RISC-V?

RISC-V is an open standard instruction set architecture (ISA) based on Reduced Instruction Set Computer (RISC) principles. RISC-V uses a smaller and simpler instruction set compared to Complex Instruction Set Computer (CISC) architectures, such as x86 and ARM. This allows for more efficient and faster processing of instructions and smaller and more power-efficient designs.

The RISC-V ISA was first introduced in 2010 and currently supports 32, 64, and 128-bit CPUs. This makes it versatile and applicable for a wide range of applications, from low-power embedded devices to high-performance computing.

One of the key features of RISC-V is its load-store architecture. In this architecture, the processor cannot directly operate on data in memory and instead requires the user to move data from memory to its internal registers before it can operate on them. This might make RISC-V slower than CISC, but it allows RISC-V to be simpler in hardware design and therefore uses less silicon space. This makes RISC-V processors more suitable for low-power and cost-sensitive applications, such as IoT devices, embedded systems, and edge computing.

Another key feature of RISC-V is that it is open-source and royalty-free, meaning anyone can use, modify, and distribute. 

ARM vs RISC-V (3 Important Factors)

Open-Source vs Proprietary

While both processor technologies are somewhat similar in function (i.e. both being load-store and RISC), the major difference between RISC-V and ARM is that RISC-V is open-source, whereas ARM is proprietary. Any designer wishing to integrate an ARM CPU into their design (i.e. an SoC) must pay royalties to ARM holdings. Additionally, ARM's proprietary nature also means that there are limitations on how the CPU can be used, and designers are required to adhere to strict license agreements.

On the other hand, RISC-V is open-source and does not require royalties or licenses, allowing for greater flexibility and customisation. Designers can experiment and develop RISC-V systems for free and can even modify the instruction set architecture to match specific application requirements. However, the lack of the proprietary nature of RISC-V also means that there is little to no support for hardware design. ARM provides teams of engineers developing hardware systems that make it easy for designers to incorporate ARM CPUs. This can be a significant advantage for designers unfamiliar with developing hardware.

Support

The second major difference between RISC-V and ARM is support. RISC-V is a relatively new processor platform, and as such, there is currently limited support for software and programming environments. This means that developers may have difficulty finding resources and tools to help them work with RISC-V processors. The lack of support can make it more difficult for developers to debug and optimise their code for RISC-V processors, leading to longer development times and higher costs.

On the other hand, ARM has a well-established and mature support structure. The ARM architecture has been around for decades, and as such, it has a large and active online community of developers, engineers, and researchers. This community has created a wealth of resources and tools to help designers target various platforms, including microcontrollers, microprocessors, and servers. A wide variety of libraries and software development kits (SDKs) are also available for ARM processors, making it easier for developers to work with them.

In addition to the online community, ARM has an extensive network of partners and vendors providing support, training, and consulting services. This can be a valuable resource for companies looking to use ARM processors in their products, as it can help them overcome any technical challenges and ensure that their products are optimised for performance and power efficiency.

Accessibility

The third major factor is If ARM is to survive the competition posed by RISC-V, it will have to rely on its overwhelming market share to present itself as a better designer choice. This strategy has worked well for Intel, which has a dominant market share in the x86 processor market. However, it may not be as effective for ARM, as Intel not only developed the architecture but also developed physical CPUs. This means that Intel has complete control over the entire design and manufacturing process, giving it a significant advantage over other competitors.

ARM, however, does not develop any hardware and instead licenses its IP to other companies, which then manufacture and sell ARM-based processors. This can be a disadvantage for ARM, as designers may prefer to work with a company that has control over the entire design and manufacturing process, as it can provide more control over the final product. Additionally, the licensing model of ARM can be perceived as a limitation for the companies that want to use ARM technology, as they may have to pay royalties and may not have the freedom to customize the architecture to their specific needs.

RISC-V vs ARM Performance

RISC-V processors, which are based on the Reduced Instruction Set Computer (RISC) architecture, generally have a higher instruction-per-cycle (IPC) performance compared to ARM processors, which are based on the Complex Instruction Set Computer (CISC) architecture. This is because RISC-V processors have a simpler instruction set architecture, allowing them to execute instructions faster and more efficiently. Because RISC-V processors have fewer instructions to execute, they require fewer cycles to complete a task, resulting in a higher IPC performance. Additionally, RISC-V processors have a simpler pipeline, which allows them to execute instructions in parallel, further increasing their performance. In contrast, ARM processors have a more complex instruction set and pipeline, which can lead to increased power consumption and lower performance.

When it comes to performance metrics, RISC-V and ARM have some key differences:

  • Instruction set architecture (ISA): RISC-V has an open-source, customisable ISA, while ARM's ISA is proprietary and only available under license.
  • Power consumption: RISC-V processors generally consume less power than ARM processors due to their simpler architecture and the ability to customise the ISA to match specific application requirements.
  • Clock speed: ARM processors typically have higher clock speeds than RISC-V processors, which can provide better performance for certain applications, such as high-performance computing or data-intensive tasks.
  • Area and cost: RISC-V processors tend to have smaller die sizes and lower production costs than ARM processors, making them more suitable for low-power and cost-sensitive applications.
  • Memory Management Unit (MMU): ARM processors have advanced memory management units which is not the case in RISC-V processors. This could be a limitation for some specific applications.
  • Performance per watt: RISC-V processors typically perform better per watt than ARM processors.
  • Security: ARM processors have a proven track record in providing security features such as memory protection and cryptographic acceleration. RISC-V processors are still in the process of building similar features.

As technology improves and support for RISC-V grows, designers will have the option to choose between a paid-for processor architecture or a free, open-source architecture with no limitations. However, just because something is free doesn't mean it will automatically become more popular. 

The use of RISC-V is increasing, and a recent job opening at Amazon is looking for candidates with RISC-V experience. This move shows that major companies are already looking at alternatives to ARM, and the attempted purchase of ARM by NVIDIA does not help this. It indicates that RISC-V is becoming more popular in the market, and major companies recognise its potential. 

The Linux operating system is a classic example, as although most distributions are free, Linux makes up a small percentage of operating systems worldwide.

Exploring the Potential of RISC-V: From Microcontrollers to High-Performance Computing

RISC-V is becoming more well-known as an open-source instruction set architecture that offers a potential replacement for proprietary architectures in a number of industries. Processors can be customised for specific needs because of their adaptive and modular design, which enhances performance, power efficiency, and security. Because of this, more companies and academic institutions are making investments in RISC-V-based solutions, spurring advancements in edge computing, AI, and the Internet of Things. As a result, a strong ecosystem of tools, libraries, and programmes has grown. This list highlights the variety of applications for RISC-V and how it has the potential to completely transform the computing industry.

Microcontrollers and Embedded Systems: One of the areas where RISC-V is already being used is in microcontrollers and embedded systems, which are small, low-power devices designed to perform specific functions. SiFive, a company that designs RISC-V processors, has developed a microcontroller called the FE310, which is based on the RISC-V ISA. The FE310 is designed for low-power applications and can be used in smart home devices, wearables, and IoT devices.

Data Centers: RISC-V is also being explored for use in data centres, which are large facilities that house computer systems and related equipment. One of the advantages of RISC-V in data centres is its flexibility, which allows for customisation to meet specific requirements. Esperanto Technologies, a company that designs RISC-V processors, is developing a chip called the ET-SoC-1, which is designed for use in data centres and can perform machine learning tasks.

High-Performance Computing: While RISC-V is currently being used primarily in low-power applications, it also has the potential for use in high-performance computing (HPC). The RISC-V Foundation has launched the OpenHW Group, which is developing open-source HPC processors based on the RISC-V ISA. These processors could be used in supercomputers, which are large computer systems used for scientific and engineering applications.

Academic Research: RISC-V is also being used in academic research, particularly in the area of computer architecture. Since RISC-V is open-source and freely available, researchers can experiment with the ISA and develop new ideas and techniques. For example, the University of California, Berkeley, developed the RISC-V ISA as a research project, and it has since grown in popularity and use.

In conclusion

While ARM's large market share may give it an advantage over RISC-V, this may not be sustainable in the long run. RISC-V has the potential to be more flexible, open-source and accessible, and ARM must adapt and make its architecture more attractive to designers to keep its market share.

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By Robin Mitchell

Robin Mitchell is an electronic engineer who has been involved in electronics since the age of 13. After completing a BEng at the University of Warwick, Robin moved into the field of online content creation, developing articles, news pieces, and projects aimed at professionals and makers alike. Currently, Robin runs a small electronics business, MitchElectronics, which produces educational kits and resources.