EVL is a way to experiment freely with dual kernel technology going back to the drawing board for the most part, which can be pretty damn fun.
In the long run, I’m hoping that the work which takes place in EVL will help in improving Xenomai which I contribute to as well. For instance, substituting the venerable I-pipe with Dovetail as Xenomai’s dual kernel interface is a valuable goal.
You can register on the EVL mailing list to discuss EVL-related topics including Dovetail and the real-time EVL core.
In several ways implementation-wise, starting from the interface which connects the Linux kernel to the autonomous core: EVL is developing Dovetail, Xenomai relies on its ancestor, the interrupt pipeline.
Although the EVL core inherits some basic code from Xenomai’s Cobalt core, both implementations are already quite different, and poised to diverge even more over time:
the EVL core only implements a handful of basic features in kernel space known as elements, which should be sufficient to provide high-level API services from user-space. At the opposite, Xenomai’s Cobalt core implements a POSIX interface directly from kernel space which amounts to 100+ system calls.
another major difference is the lack of specific driver model in the EVL core, which fits in the regular Linux model. Xenomai relies on the RTDM layer instead, which is entirely separate.
high scalability with large multi-core systems is a strong goal of the EVL core, and the current single-lock model Cobalt exhibits won’t fit that bill. For this reason, their respective scheduler infrastructures are already diverging.
EVL and Xenomai differ in purpose too. On the one hand, Xenomai aims at a comprehensive real-time framework offering multiple APIs, RTOS emulators and various protocol stacks, based on a POSIX-compliant core and the I-pipe dual kernel interface, tracking LTS kernel releases. Xenomai APIs can even run in single kernel configurations such as PREEMPT_RT.
On the other hand, EVL is about enabling any autonomous software core to run along the most recent mainline kernel release, according to clear interface rules defined by the latter. In other words, EVL is all about, and only about dual kernel technology. To showcase this, EVL comes with a compact real-time core delivering basic services via a small library implementing its ad hoc API, for anyone to play with and build on.