Zephyr v4.4.0-rc1 was officially released. Over the past six months, the R&D team at SiFli has been deeply engaged in foundational work—we have fully ported and merged the low-level code of the SF32 series chips (primarily the SF32LB52x series for now) into the Zephyr mainline.
Taking the opportunity of the v4.4 release, we’d like to have a brief chat with you, our fellow developers, about our progress and SiFli's future plans for building an open-source ecosystem.
Why invest the effort into Zephyr integration?
As an original chip manufacturer, we face developers' pain points head-on. As IoT devices become increasingly complex, traditional bare-metal development or simple RTOS often struggle to handle intricate network stacks, file systems, and multi-device collaboration.
Backed by the Linux Foundation, Zephyr has grown rapidly in recent years. It introduces Linux-like mechanisms such as the Device Tree, a highly modular configuration system (Kconfig), and incredibly rigorous driver model standards. These features give it a distinct edge in complex IoT application development. SiFli’s chips are defined by their high integration and low power consumption. By fully supporting Zephyr, we aim to provide developers with a standardized, modern low-level software platform, significantly lowering the barrier to cross-platform development.
What specific work have we done over the past six months?
From setting up the repository in September 2025 to now, the team has strictly adhered to community standards, submitting over 200 commits (approximately 209) upstream and successfully merging 36 Device Tree binding files.
From the kernel to peripherals and Bluetooth: Full integration of Zephyr's features:
- Comprehensive Peripheral Driver Support: We have completed the definitions for 8 sub-models and ported over 22 core peripheral drivers. To ensure real-world performance, we didn't just implement polling and interrupts for communication interfaces like UART, SPI, and I2C; we also enabled asynchronous APIs and hardware DMA support. Furthermore, multimedia and security-related drivers, such as the LCDC display controller, MIPI DBI, Audio Codec, TRNG, and eFuse, have all been successfully merged into the mainline.
- Rich Board-Level and Product Implementations: The mainline code now includes not only SiFli's official development board (
sf32lb52_devkit_lcd) but also Board Support Packages (BSPs) for third-party mass-produced products based on the SF32LB52x chip (such as the Pebble Time 2 smartwatch). - Complete Integration of the Bluetooth Stack: Zephyr's native open-source Bluetooth stack is one of the core strengths of its ecosystem. In this integration, we not only bridged the underlying Bluetooth HCI via the Mailbox IPC mechanism but also achieved full docking and support for Zephyr's Bluetooth protocol stack. Currently, everything from basic BLE communication to complex Bluetooth Mesh networking is supported on SiFli chips. Developers can directly call standard Zephyr Bluetooth APIs for application development.
Note: The submission of several key drivers mentioned above, such as LCDC, Audio CODEC, and Bluetooth Mailbox, has been officially featured in the Zephyr v4.4 Release Notes.
Embracing Open Source and Committing to the Long Term
Pushing code to an open-source mainline is an exercise in patience. The community's rigorous Code Review process demands high code quality and test coverage. Throughout this journey, our team resolved numerous potential issues and enriched the corresponding tests and sample applications.
For SiFli, getting the code merged into the mainline is just the first step. In the open-source world, long-term maintenance is often far more critical than the initial commit. Currently, our code status in the Zephyr community is officially marked as maintained. We are fully committed to tracking community updates, fixing bugs, and optimizing performance. Moving forward, we will gradually push more chip series, such as the SF32LB55x and SF32LB58x, into the Zephyr mainline.
The official release of Zephyr 4.4 is just around the corner. We sincerely invite all developers to pull the latest code, experience it, and build on the SiFli platform. If you run into any issues, feel free to open an Issue in the community or reach out to us directly. Help us build a stronger foundational ecosystem together
