[LeifCarrotson]

I completely agree, it depends on your expectations.

With the caveat that it's not a one-way trade-off of "better" vs. "good enough for the expectations". If your customer calls you and says "My industrial CNC controller crashed and ruined a $20k prototype, is this my fault or yours? Here are the logs." and your answer is "the browser was running bad javascript that locked up too many threads for too long so it stopped counting the encoder for 20 ms", they're going to tell you that a servo amplifier has no business doing any of that stuff.

Some devices do need to be on the Internet and should therefore be running general-purpose operating systems. They may need to interact with other devices that run real-time operating systems (or bare metal, like the Teensy). Some IoT devices try to bridge the gap. Knowing and deciding which side you're on is critical.

And I think the best answer to pennypinching on the BOM is to separate your concerns into separate devices/apps. Make the CNC HMI handle the Internet connectivity. Give it one NIC that hooks up to the Wifi, let it run whatever Javascript you want. On a separate NIC, talk whatever flavor of industrial protocol you prefer on the machine. Do not bridge the two. In the servo amp, use a bare-metal/RTOS microcontroller. That device doesn't need to be burdened with Linux, and in fact is made worse by it: Let it be what it is and no more. In 20 years, it should still run reliably, regardless of whatever newfangled holographic VR HMI is loading in motion profiles.

[ohazi]

Exactly, use the right tool for the job.

FPGAs and microcontrollers are really good for meeting (and verifying that you're meeting) hard real-time constraints.

Network connectivity (by definition) can't be real-time, so you wouldn't want to run a network stack on the real-time core anyway, even if you could.

Instead of adding another non-real-time microcontroller for networking and making it sweat, go with an application processor and just treat it like a dumb modem that happens to know how to handle VPN traffic without exploding.

There are application processors like the i.MX7 and the STM32MP1 that combine a Cortex-M4 and a Cortex-A7 on the same die for precisely this reason (and similar FPGA fabric + PowerPC / ARM Cortex-A? products from Xilinx and Altera for even longer).