Zephyr Project at FOSDEM 2025: A Recap Blog

Zephyr RTOS Roasting Party

You’ve heard it from colleagues, you’ve seen it on Reddit… Zephyr RTOS can be difficult to navigate.

Join this session for a “Zephyr Roasting Party” where we’ll openly look at and discuss the most complained-about aspects of Zephyr, and try to honestly answer common questions and criticisms such as:

• “Zephyr is bloated and really has poor real-time performance compared to other RTOSes”
• “I already have a HAL from my silicon vendor, why would I need even more HW abstractions?”
• “Devicetree is so complex! How do I even understand what’s going on with all these ‘macrobatics’?”
• “There’s lots of drivers available upstream, sure, but how do I know how mature they are?”
• “What is this west thing, and why are you asking me to learn Python?”
• “Why is my board/driver not supported?”

The goal of the talk is NOT to rhetorically question some of the “bad” parts of Zephyr, only to immediately tell you why Zephyr is in fact the best thing since sliced bread. Instead, we will honestly discuss these pain points to help you understand better some of the design decisions behind Zephyr, and why they might (or might not!) actually be worth the steep learning curve.

Open-Source CPU: Deep-dive into RISC-V CFU and Zephyr

RISC-V’s instruction set architecture (ISA) has enabled seasoned embedded software engineers to experiment with FPGAs since numerous open-source RISC-V cores can be flashed onto an FPGA.

The Zephyr Project is rapidly emerging as a leading real-time operating system (RTOS). Zephyr integrates open-source and security best practices to ensure a vendor-neutral, secure, and reliable platform.

One of the exciting features of the RISCV ISA is the Custom Function Unit (CFU), which enables a framework to support custom operations in hardware, which is accessible from software. In this talk, Mohammed will provide an in-depth demonstration on how to add a CFU into a RISCV core on an FPGA, how to make the appropriate calls from Zephyr, and the possibilities that the CFU enables for hardware acceleration in embedded systems.

Developing BLE Host Applications with Zephyr

Bluetooth Low Energy, commonly abbreviated as BLE, is a well-known wireless communication technology aimed at low-power applications. It divides devices into two categories: low-cost, potentially high volume, battery constrained peripheral devices such as head phones or heart rate monitors, and comparatively more powerful and less constrained central devices, such as smartphones and notebooks.

The Zephyr Project has supported developing BLE peripheral applications for a long time. But it may not be well known that it also supports BLE host applications, or central devices as the standard calls them. In his talk, Florian will take a look at how we can develop BLE host applications using Zephyr. After a (very) short introduction to the BLE protocol stack, he will delve into Zephyr’s Bluetooth API and more importantly talk about the pitfalls he encountered while getting his feet wet with Zephyr. On the practical side, this talk will look into how BLE applications remain portabile between boards by different vendors, and how the many BLE-enabled emulators and simulators provided by Zephyr can be used for quicker development and testing.

In this talk you will learn about:

• the basics of the BLE protocols
• the Zephyr Bluetooth API and its pitfalls
• how portable Zephyr applications using BLE are
• how you can utilize the Zephyr emulators and simulators for BLE development

The USB-MIDI 2.0 device class in Zephyr

A few years ago, a musician friend of mine reached out, hoping to build a custom controller for a live act performance. Together, we decided on a USB-MIDI device, which soon became a hands-on learning journey into Zephyr, USB development, and the MIDI protocol.

MIDI (Musical Instrument Digital Interface) has been the leading standard for connecting digital instruments and controllers since the 1980s. Although USB includes MIDIStreaming (a subclass of the Audio device class), Zephyr had no support for it. So, I decided to build one.

In this talk, I’ll walk you through my adventures implementing (and eventually upstreaming) this new device class. We’ll start by revisiting the original MIDI 1 protocol from the eighties, the original USB-MIDI1.0 from the 2000s and the updated USB-MIDI2.0 specification from 2020. After a brief refresher on USB devices, I’ll introduce the USB MIDIStreaming interface and the various supported topologies. Finally, we’ll see how to bring it all together using Zephyr USB device_next, and how it is used from your application’s code. In the end, we should be able to make any kind of MIDI speaking device using our favorite kite-stamped RTOS.

Alongside this technical content, I may relate my experience as an occasional hobbyist contributor since Zephyr 1.14, and how I navigated spec updates (Device tree changes, USB-MIDI 1.0 to 2.0, Zephyr USB device next).

Embedded Video Systems With Zephyr

Zephyr is a real-time operating system providing Video APIs to embedded devices. It enables building video feeds out of any supported hardware, low-power or high-performance alike.

The image sensor market explodes and cameras are used for many purposes: optics, electronics and signal processing is empowering medical imaging, agriculture, drones, conferencing, traffic monitoring, robotics, automation, scientific equipment… Through computer vision, imaging becomes an integral part of an information system around it: images that act.

A Zephyr-themed overview of the video information chain, from photons to software APIs.

(Note: Video recording will be shared here as soon as the FOSDEM page publishes the talk)