Microsemi – The Case for RISC-V in the Industrial Market

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By: Ted Marena, Director of SOC/FPGA Product Marketing & Business Development Microsemi, Vice-Chair RISC-V Marketing Committee

The industrial market has many unique needs that are not present in other vertical markets. Characteristics such as longevity of supply, long life product cycles, robust and reliable technologies, just to name a few. These designs also want technology that they can depend on for support for long periods of time. When it comes to processors being used in the industrial segment, there is a major shift which designers should be aware of. This new processor ecosystem is called RISC-V. Microsemi is a leading vendor adopting RISC-V. They have recently introduced their Mi-V RISC-V ecosystem which consists of tools, processor cores, solutions and more (www.Mi-V.org).

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Today, the vast majority of processor architectures is an Intel x86 variation or an ARM, mainly A class processor. Although it is unlikely these proces- sors will not be very popular in the future, the RISC-V processor ecosystem is poised for rapid growth in the industrial market. The RISC-V processor is founded not on an architecture but on a fixed instruction set (ISA). The design of the processor architecture is flexible. You can use an architecture that has some operations accelerated in hardware or a processor designed for lower power consumption. All of the variations in the RISC-V micro architecture are acceptable because the ISA is fixed. To enable broad use of RISC-V, the RISC-V foundation, froze the instruction set in 2014 so the market could dictate the processor architectures. The RISC-V organization is a non-profit foundation controlled by more than a hundred member companies, including many tier-1 organizations. It directs the future development of HW/SW specifications and the ecosystem, and drives the adoption of the RISC-V ISA. With the ISA set in stone, engineers can now implement processor architectures optimized for their requirements.

Mi-V Ecosystem Components

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Most industrial designs are leveraging Linux for their operating systems. Because of this market shift, designers and architects are free to choose any processor which is supported by Linux. In addition, with the widespread adoption of Linux, it is rendering the choice of the ISA and the processor itself to be simplified. If the processor supports Linux, then it can be considered. With each new version of ARM processors, the instruction set tends to grow. This actually requires new versions of Linux to support the newer architectures. Because the RISC-V ISA is frozen, code migration from one RISC-V core to another is much more seamless than migrating from one ARM to another. Because of the dominant Linux OS, the industrial market can rapidly adopt RISC-V as a new standard open architecture for direct native hardware implementations. This is one of the main reasons RISC-V is attractive for the industrial market. However, there are additional factors which make RISC-V more attractive than other processor architectures, even if you do not use Linux in your design. These can be summarized as follows:

Why RISC-V?

Simplicity: Because the ISA is fixed and contains less than 50 instructions and multiple standard extensions, it offers a stable, clean-slate design platform with clear and secure separation between User and Privileged modes. Designs are very simple to develop because all of the instructions have been frozen. Additions to the standard instruction set are made through extensions—not new ISA versions—for additional stability in future designs. These few instructions allow simple architectures to be created, which in turn leads to very cost effective and power-efficient processors. The industrial market can benefit from the fixed ISA and count on this consistency for years to come.

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Portability: Designs which could ramp into high volume will benefit from the portability of RISC-V. Start a design in an FPGA with a soft gate version of a RISC-V core and begin shipping the product. Because the software will be completely portable across all devices that have a RISC-V core, this creates “royalty-free” processor sub-system RTL code that can be implemented in hardware. Designers can modify, adapt, and migrate their design to the best platform available for their product. If the selected FPGA becomes obsolete, there is no need to rewrite the software code. You have the entire source RTL. Simply retarget this to another FPGA. Alternatively, if the volumes reach high enough levels, simply retarget the RTL source to an ASIC without paying any royalty fees! This is simply not possible with an ARM or x86 type processor.

Certification and Safety: For industrial designs which require functional safety, RISC-V’s flexibility enables unique solutions. For example, one could design a system with multiple, functionally-equivalent cores autonomously designed for the ultimate in redundancy. One core could be the Microsemi RV32IM, and the other core could be a functionally-equivalent, yet com- pletely different, in-house design. RISC-V also allows complete flexibility over the micro architecture, so one could provide single event upset (SEU) protective measures for data and instruction cache memory. Many other safety prevention techniques can be used because RISC-V allows access to the RTL. For industrial designs which must be certified, providing the RTL for the RV32IM from Microsemi will enable inspection so the core can be more easily certified. These are the key benefits of the RISC-V ISA. Now, you may be asking yourself, “OK, how do I learn more about using a RISC-V core for my next design?” There are several places to get started. For background information about RISC-V and its member organizations, go to www.riscv.org. If you want to simply jump into a design and begin coding for a RISC-V core, head over to Microsemi’s Github site, github.com/ RISCV-on-Microsemi-FPGA. Microsemi was the first FPGA vendor to offer an open architecture RISC-V IP core and a comprehensive software IDE solution. Designers can deploy the RISC-V IP core in multiple flash based FPGAs, including the PolarFire FPGAs, IGLOO2 and SmartFusion2 devices. These devices also enable one to store the boot code for the RV32IM in secure eNVM which could prevent malware or a root kit from being installed. Embedded engineers can leverage the benefits of this open HDL architecture in their custom FPGA designs by using the Libero SoC Design Suite.

If you just want to review a RISC-V core and write software executable code, Microsemi has created a series of reference designs. My favorite and the least expensive is for the Creative board RISC-V reference design, as shown in the following figure. By leveraging the Future Electronics Creative development kit and an Arduino touch screen display, Microsemi has implemented their RV32IM core and compiled source code to run a tic-tac-toe game. For software code development, the Eclipse-based Soft Console integrated development environment (IDE) hosted on a Linux or Windows platform provides complete development support, including a C or C++ compiler and debugger capability.

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IGLOO2 Core RISC-V Tic-Tac-Toe

The complete reference design can be created by purchasing the Creative board (www.FutureElectronics.com/CreativeDevelopmentBoard) and the Arduino shield display (www.adafruit.com/products/1651). Together, these cost only $135. The Microsemi RISC-V IP core, Libero SoC development software, and the Soft Console IDE can all be downloaded free of charge from the Microsemi Github site.

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Creative RISC-V board with IGLOO2 FPGA Block Diagram
Industrial designers now have a compelling new alternative processor architecture to consider with the mainstream adoption of RISC-V. If you run Linux in your system, selecting an appropriate RISC-V device provides you a compelling alternative to ARM. The advantages of design portability, retargeting to different hardware and lower power can benefit virtually every industrial application. Customers can also count on the fixed ISA to ensure longevity of the architecture. The RISC-V processor is especially compelling for applications where functional safety, certification and security is important. For industrial engineers who prefer to collaborate and are able to leverage the open source community, RISC-V is the logical choice. Regardless of your reason, there is no doubt that using a RISC-V core unleashes a new generation of innovation for embedded industrial designers.

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