Azure RTOS Open‑Sources as Eclipse ThreadX: Impact on Raspberry Pi and Embedded Developers

Microsoft is open‑sourcing the real‑time operating system it acquired from Express Logic and donating it to the Eclipse Foundation. The donation includes the ThreadX RTOS and the Azure RTOS development kit.

Eclipse has renamed the project Eclipse ThreadX (https://threadx.io/).

Many RTOSes exist in the market, yet developers often know little about them. You may have never heard of ThreadX, but it is likely already present in multiple devices, possibly even running today.

Well‑known RTOS examples include Wind River’s VxWorks, which runs on NASA’s Perseverance rover, and BlackBerry’s QNX RTOS, historically used in smartphones and other products.

In the 1990s QNX was demonstrated on a single‑floppy‑disk demo (http://qnx.puslapiai.lt/qnxdemo/qnx_demo_disk.htm).

Microsoft claims ThreadX is extremely widespread, running on roughly 12 billion devices worldwide.

It powers Intel’s chip management engine and controls the firmware of Raspberry Pi devices: on Pi 1‑3 it appears as the bootcode.bin file on the SD card, while on Pi 4 and 400 it is the start*.elf file. In Debian on GitHub it also exists as a proprietary “blob” that runs on the VideoCore GPU, acting as a sealed black box that boots the Pi and manages its hardware.

In 2019, the 21‑year‑old operating system was acquired by Microsoft, which renamed it Azure RTOS, though the rebranding brought little benefit.

The acquisition followed Amazon’s takeover of FreeRTOS, clearly a competitive response. After the deal, original developer William Lamie left to start a new company selling a POSIX‑compatible “fifth‑generation” RTOS called PX5OS.

Nevertheless, ThreadX remains a thoroughly tested and mature product; some components, such as the STM32 version, have TÜV functional safety (FuSa) certification, which is attractive to many customers.

The current version is open‑sourced on GitHub, but a VideoCore version has not yet appeared. There is hope that the Raspberry Pi Foundation will obtain permission to release its source code.

As of last year, the Raspberry Pi Foundation has sold over 46 million units; an open software stack would make these products even more appealing.

Open‑sourcing brings several advantages: broader, uninterrupted access to ThreadX technology, accelerated innovation through community participation, a transparent collaborative development process, and wider coverage that makes the OS easier to adopt in various applications.

Starting in Q1 2024, the Eclipse ThreadX project will be offered under the MIT license, including ThreadX, NetX Duo, FileX, GUIX, USBX, LevelX, and related tools and documentation. Microsoft has pledged to continue supporting the project with the latest certifications to ensure safety and security continuity.

GitHub repository: https://github.com/azure-rtos