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Open source Zephyr RTOS snuggles up to RISC-V with new members

Aug 17, 2018 — by Eric Brown 2,598 views

The Zephyr Project announced six new members including RISC-V boosters SiFive and AntMicro, and expanded development support to more than 100 boards.

The Linux Foundation’s Zephyr Project, which is developing the open source Zephyr real-time operating system (RTOS) for microcontrollers, announced six new members, including RISC-V members Antmicro and SiFive. The project also announced expanded support for developer boards. Zephyr is now certified to run 100 boards spanning ARM, x86, ARC, NIOS II, XTENSA, and RISCV32 architectures.

Antmicro, SiFive, and DeviceTone, which makes IoT-savvy smart clients, have signed up as Silver members, joining Oticon,, Synopsys, and Texas Instruments. The other three new members — Beijing University of Posts and Telecommunications, The Institute of Communication and Computer Systems (ICCS), and Northeastern University — have joined the Vancouver Hack Space as Associate members.

Zephyr architecture (Mar. 2018)
(click image to enlarge)

The Platinum member leadership of Intel, Linaro, Nordic Semiconductor, and NXP remains the same. NXP, which has returned to an independent course after Qualcomm dropped its $44 billion bid, supplied one of the first Zephyr dev boards — its Kinetis-based FRDM-K64F (Freedom-K64F) — joining two Arduino boards and Intel’s Galileo Gen 2. Like Nordic, NXP is a leading microcontroller unit (MCU) chipmaker in addition to producing Linux-friendly Cortex-A SoCs like the i.MX8.


RTOSes go open source

Zephyr is still a toddler compared to more established open source RTOS projects like industry leader FreeRTOS, and the newer Arm Mbed, which has the advantage of being sponsored by the IP giant behind Cortex-M MCUs. Yet, the growing migration from proprietary to open source RTOSes signals good times for everyone.

Thea Aldrich

“There is a major shift going on the RTOS space with so many things driving the increase in preference for open source choices,” said Thea Aldrich, the Zephyr Project’s new Evangelist and Developer Advocate, in an interview with “In a lot of ways, we’re seeing the same factors and motivations at play as happened with Linux many years ago. I am the most excited to see the movement on the low end.”

RISC-V alignment

The decision to align Zephyr with similarly future-looking open source projects like RISC-V appears to be a sound strategic move. “Antmicro and SiFive bring a lot of excitement and energy and great perspective to Zephyr,” said Aldrich.


With SiFive, the Zephyr Project now has the premiere RISC-V hardware player on board. SiFive created the first MCU-class RISC-V SoC with its open source Freedom E300, which powers its Arduino-compatible HiFive1 and Arduino Cinque boards. The company also produced the first Linux-friendly RISC-V SoC with its Freedom U540, the SoC that powers its HiFive Unleashed SBC. (SiFive will soon have RISC-V-on-Linux competition from an India-based project called Shakti.)

Antmicro is the official maintainer of RISC-V in the Zephyr Project and is active in the RISC-V community. Its open source Renode IoT development framework is integrated in the Mi-V platform of Microsemi, the leading RISC-V soft-core vendor. Antmicro has also developed a variety of custom software-based implementations of RISC-V for commercial customers.

Renode workflow diagram
(click image to enlarge)

On Aug. 14, Antmicro and SiFive announced a partnership in which SiFive will provide Renode to its customers as part of “a comprehensive solution covering build, debug and test in multi-node systems.” The announcement touts Renode’s ability to simulate an entire SoC for RISC-V developers, not just the CPU.

Zephyr now supports RISC-V on QEMU, as well as the SiFive HiFive1, Microsemi’s FPGA-based, soft-core M2GL025 Mi-V board, and the Zedboard Pulpino. The latter is an implementation of PULP’s open source PULPino RISC-V soft core that runs on the venerable Xilinx Zynq based ZedBoard.

Other development boards on the Zephyr dev board list include boards based on MCUs from Microchip, Nordic, NXP, ST, and others, as well as the BBC Microbit and 96Boards Carbon. Supported SBCs that primarily run Linux but can also run Zephyr on their MCU companion chips include the MinnowBoard Max, Udoo Neo, and UP Squared.

Zephyr 1.13 on track

The Zephyr Project is now prepping a 1.13 build due in September, following the usual three-month release cycle. The release adds support for Precision Time Protocol PTP and SPDX license tracking, among other features. Zephyr 1.13 continues to expand upon Zephyr’s “safety and security certifications and features,” says Aldrich, a former Eclipse Foundation Developer Advocate.

Aldrich first encountered Zephyr when she found it to be an ideal platform for tracking her cattle with sensors on a small ranch in Texas. “Zephyr fits in really nicely as the operating system for sensors and other devices way out on the edge,” she says.

Zephyr has other advantages such as its foundation on the latest open source components and its support for the latest wireless and sensor devices. Aldrich was particularly attracted to the Zephyr Project’s independence and transparent open source governance.

“There are a lot of choices for open source RTOSes and each has its own strengths and weaknesses,” continued Aldrich, “We have a lot of really strong aspects of our project but the community and how we operate is what comes to mind first. It’s a truly collaborative effort. For us, open source is more than a license. We’ve made it transparent how technical decisions are made and community input is incorporated.”

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