Well, that too :) What I’m referring to is more like Qualcomm “safety island” on Dragonwing, Xilinx RPU, or Allwinner AR100 (I think this is used in 3D printer projects using A64, actually), though - where most modern large “embedded” Linux SoCs have some real time island to talk to the outside world. Cell phone SoCs and stuff like Apple M also have realtime cores hiding in them running blobs, although they’re usually connected to more specific RF or A/V blocks rather than generic IO.