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Comment by gaudat | Hacker News Reader

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.

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It’s a little outdated but this blog post is a pretty good overview of the options available [1].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

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.

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.

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