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Comment by zokier | Hacker News Reader

Editorialized title; its not part of the MCU family, its part of the MPU family

And the line between the two is blurred now with MCU running at hundreds of MHz. The STM32H7 is has more IPC than the original Raspberry Pi.

Do you take external DDR RAM on an application-class ARM core? You're an MPU.

There's a blurry line sometimes, but Application-class (Cortex A* cores, like A5, A35, etc. etc.) are solidly MPU. Not even close.

> Do you take external DDR RAM on an application-class ARM core? You're an MPU.

The actual difference IMHO is the existence of an MMU. (Which is, fdpic/linux-nommu efforts notwithstanding, the general "Linux" condition.)

(Ex.: the SOPHGO SG2000 RISC-V chip comes with integrated DDR3 RAM, but is still solidly an MPU. I believe there are some ARM Cortex-A with integrated RAM too, can't think of any off the top of my head. [Ed.: nevermind, the SG2000 is dual RISC-V/ARM])

Nuvoton have some ARM9 parts with integrated DRAM for example [0].

It’s a little outdated but this blog post is a pretty good overview of the options available [1].

[0] - https://www.nuvoton.com/products/microprocessors/arm9-mpus/

[1] - https://jaycarlson.net/embedded-linux/

If it runs Linux, it's MPU. If it runs bare firmware, it's MCU.

No this not a really good criteria. There is Linux support for a few MCUs, including a few STM32 Series. Having a MMU is a much better criteria.

Then the 8-bit ATMega328p in the Arduino Uno is an MPU[1]. Except it's solidly an MCU. I'd say if it uses external RAM as its main memory, and external storage as its main storage, then it's an MPU. If the RAM is all internal, and the storage is all (or can be all) internal, it's an MCU.

[1] https://github.com/raspiduino/arv32-opt

That’s a gimmick. I’m talking about how given chip is supposed to be used in a real products, whether vendor supplies Linux builds in one way or another, etc.

It's even more blurred with this vhip because it sound like it has both a 64-bit Cortex-A35 MPU and a 32-bit Cortex-M33 MCU core.

As an aside, I'm pretty sure these chips were announced months ago despite what the article says.

Yes, my bad, thanks. Don't think I can change it now, though.

What’s the diff between an SoC and MPU? Lack of a wireless connectivity subsystem?

Well, SoC is different again. We're talking MCU, microcontrollers.

For ARM, its rather simple. Cortex-M cores are MCUs, while Cortex-A cores are Microprocessors.

Cortex A72?? That's a Microprocessor.

Cortex M7? This is a Microcontroller.

MPU -> Microprocessor. MPUs typically have features that let it support a "full" OS; MMUs, speculative execution, advanced CPU pipelining features, etc. They also have a much higher RAM capacity. Often has more complicated power requirements when doing board design due to needing different voltage busses for different peripherals. Usually can't be run standalone, you have to bring some of your own peripheral hardware. For example, you usually need to bring your own RAM.

MCU -> Microcontroller. Low power, less RAM, limited MMU/memory protection features, typically run baremetal firmware or an RTOS. Usually so simple it only needs a single voltage rail. More or less self-contained. Has RAM and ROM on-die.

SoC -> System-on-a-chip. Actually a very vague term. But in broad strokes, an SoC is what it says: An entire system on a single chip. Could incorporate an MCU or an MPU, plus other peripherals, etc. You can almost think of it as a "single chip computer" as opposed to a "single board computer". It's almost more of a marketing term than an EE term. For example, the Apple Silicon stuff is a "SoC" because it has the MPU + GPU + RAM on a single die.

I tend to think of an SoC as "MCU with other peripherals not typically on an MCU", so BLE/WiFi radio or maybe gate drivers for motor control. But usually radios. As you pointed out "not typically on an MCU" is a moving target. Was a point where RAM and a decent ADC would be things you had to add externally.

The definition of MPU is basically CPU, no?

MPU is a processor so you supply data to process.

MCU is a controller so you supply target to control.

SoC is a system so you supply tasks to execute.

disclaimer: above is all I hallucinating.

Indeed, this is an embedded SOC, not an MCU. Very nice device.

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