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Comment by zwieback | Hacker News Reader

The idea is to move realtime-ish stuff to a popular processor many people have worked with and moving the Linux stuff over to an appropriate platform.

When it came out we used STM32MP257 to demo a quadrature encoder debugger/logger (for internal use, not a product) since the IO supports easy interfacing of encoders. The micro's peripherals (SPI, I2C, GPIO etc.) are easy to program at the register level and you can run a simple mainloop+interrupts thing on the micro, then run Linux for your UI, networking, etc.

The fact that there's not much activity around these kinds of platforms (CPU+micro or CPU+FPGA) suggests it's too hard to combine the two in a way that makes sense for enough people, easier to just use standard components and have them side-by-side on the PCB.

It is nice to have them on the same die, though, for people like myself who like to work on both ends but don't know how to make their own PCBs.

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The truth is that those are just niche items. Having a need for both a Linux-grade CPU and a real time MCU-like core is not that common. It tends to show up in projects too advanced for most to attempt.

That's untrue. Almost all the products I worked with in my last company had such architecture - which we leveraged (this was Ag industry). It's very easy to work as they have shared memory to talk to each other.

That's at least a tier more advanced than mainstream.

And if by "very easy to work" you mean "just allocate a shared memory block and put a mailbox in there for the Linux userspace and the RT MCU to talk to each other", you may have inflated expectations of what an average developer using an SBC can easily do. It's "very easy" in the same way rolling your own PCBs or writing your own drivers is very easy. Seasoned developers do it without thinking twice, and then stand dumbstruck when they see entry level developers avoid that like the plague.

Not like we're lacking for the offerings. Plenty of modern SoCs have MCU-like real time cores in them - intended for low power operation, real time control, or both. Even the mainstream RPi 5 boards ship spare PIO and MCU cores - in the RP1 chip. The vendor just couldn't be bothered to document that.

What do you mean by mainstream?

There’s whole sectors of industrial and automotive using these AMP SoMs. And relative to these RPi only recently began providing options that you could design into an embedded product at all. Their FAE and supply presence is way behind.

By "mainstream" I mean "the bulk of development work done", not "the bulk of units shipped".

The boards that people reach for when they roll their first projects, the hardware that ends up in early prototypes and one-off devices, the hardware that gets targeted by open source projects. The chips that return more than a "databrief" 8 pages long and a single page on a vendor site inviting you to visit the snake pit with "contact sales for more information". The boards you can actually buy with a fixed price tag and a delivery to door, and can find writeups on how to use them for specific things.

If you know what "FAE" is, let alone can get into a meeting with one, you're deep in the trenches, and are pretty much expected to wrangle an extremely poorly documented MCU core that happens to be shipped in a SoC as an afterthought into submission.

These parts aren’t designed to be your next Raspberry Pi that mostly gets tossed in a drawer.

Engineers actually use these in real products and embedded systems.

The combination of Linux and microcontrollers isn’t new. It’s a very valuable and common structure.

The comments here trying to dismiss it or call it uncommon are bizarre.

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