[Felger]

Chuckles. Intel and AMD provide ME/AMT/SPS and PSP respectively on their whole x86-64 CPU range, which are embedded SOC : a CPU (based on quark for intel) and basic OS (said to be from Minix 3 for intel as well), nested within the CPU in the way they cannot be disabled as they are serialized to logical CPU init, "microcode style". Add obfuscated code modules, cannot be completely removed whatever everyone could do up to now. It can access to the network stack and has an "always on" behavior once the system is simply plugged to the power.

If you're security concerned, the OS stack is quite a... secondary issue to you.

You will have to consider switching to an open RISC architecture (Risc-V someone ? Strangely enough or not, EU seems quite fan of this on-the-rise-again architecture) AND a linux distribution.

For sure, for sensitive applications, having a cheap, secure and versatile architecture would be better than making DSPs or issuing hardly scalable and pricy FPGA solutions (well, lots of communication equipements' mainboards still uses them)

[Felger]

Even though for REALLY sensitive applications (defence and space), DSP stay the gold standard.