[pjc50]

For the Wifi device mentioned in the original article, they dissasembled the firmware and found out that it uses "ThreadX": https://en.wikipedia.org/wiki/ThreadX

> "hreadX provides priority-based, preemptive scheduling, fast interrupt response, memory management, interthread communication, mutual exclusion, event notification, and thread synchronization features. Major distinguishing technology characteristics of ThreadX include preemption-threshold, priority inheritance, efficient timer management, picokernel design, event-chaining, fast software timers, and compact size. The minimal footprint of ThreadX on an ARM processor is on the order of 2KB"

ie it's generic code that gets built into a unikernel-style image with the device-specific code that actually implements the various tasks required of a wifi controller.