[rkangel]

> MCU-class footprint (fits in 16 MB RAM)

That is absolutely not an MCU class footprint. Anything with an "M" when talking about memory isn't really an MCU. For evidence I cite the ST page on all their micros: https://www.st.com/en/microcontrollers-microprocessors/stm32...

Only the very very high performance ones are >1MB of RAM.

[marci]

For squeezing erlang in KiB sized RAM, the AtomVM project is probably a better fit.

https://github.com/atomvm/AtomVM

[PinguTS]

I see their board uses a daughter board from Phytec, a German company too. This is based on very high performance NXP MCU, the i.MX 6UL, with additional external DDR RAM.

[LeifCarrotson]

It's a $212 SBC. They've got more L2 cache than most microcontrollers have Flash memory.The fact that it's got an L2 cache at all, much less external LPDDR3 DRAM, is a bit ridiculous. In most parameters - cost, RAM, frequency, storage, power consumption - it's approximately 2 orders of magnitude beyond the specifications of a normal microcontroller.

[magicalhippo]

NPX calls[1] it an application processor, and is based on a Cortex-A7, not a Cortex-M series microcontroller processor.

That said these nomenclatures are a bit fuzzy these days.

[1]: https://www.nxp.com/products/i.MX6UL

[cmrdporcupine]

Eh. It's getting blurry and has been for some time. To me these days the differentiators are: does it have an MMU? Address lines for external memory? Do you write for an OS or for "bare metal" / RTOS kit? Are there dedicated pins for GPIO?

If you choose some arbitrary memory amount as the criterion it will be out of date by next year.

[derefr]

Espressif calls the ESP32 an MCU, and at least 1/3 of ESP32 models have >1MiB of onboard PS ("pseudo-static") RAM (i.e. DRAM with its own refresh circuit.) At least 20 of the ESP32 models do have 16MiB.

(And I would argue that the ESP32 is an MCU even in this configuration — mostly because it satisfies ultra-low-power-on-idle requirements that most people expect for "pick up, use, put down, holds a charge until you pick it up again" devices.)

So, sure, if you mean the kind of $0.07 MCU IC you'd stuff in a keyboard or mouse, that's definitely not going to be running Nerves (or any other kind of dynamic runtime. You need to go full bare-metal on these.)

But if you mean the kind of $2–$8 MCU IC you'd stuff in a webcam, or a managed switch, or a battery-powered soldering iron, or a stick vacuum cleaner with auto suction-level detection, or a kitchen range/microwave/etc with soft-touch controls and an LCD — use-cases where there's more-than-enough profit margin to go around — then yeah, those'll run Nerves just fine.

[ACCount37]

Even ESP32, the quintessential "punches above its weight" MCU, only packs 520KB of RAM by default. At the time of its release, that was a shitton of RAM for an MCU to have!

If you ship MCUs with 16MB of RAM routinely, you're either working with graphics or are actually insane.

[defen]

The MCU I'm currently working with has 12KB of RAM and it feels luxurious.

[ACCount37]

Ah, the cultural shock of going from 8 bit cores with 512 bytes to an actual modern chip.

[the__alchemist]

ESP32's are on the high end of FLASH and RAM counts. You are pointing out that there is variance. The kind sof 2-8$ MCUs I've used generally have 512k-2Mb[it] onboard flash and <512k SRAM. (STM32G4, H7, ESP32C3 etc)

The Sub <$1 you refer do will have <100k of these. (STM32C0, G0 etc)

ST is actually moving away from the 2Mb MCUs, and instead offering ~1Mb with Octospi. I believe the intent is to use offboard flash if you want more. (e.g. the newer H7 variants)

[imtringued]

MCU generally refers to self contained microcontrollers without any external memory. Once you add external memory, there are basically no limits anymore, but if you are going that route a LicheeRV Nano would get you a full Linux system with 256MiB for $16 so why bother targeting "MCU-class" chips?

[dlcarrier]

Espressif's ESP32 line uses an MCU IC, either sold by itself (https://www.espressif.com/sites/default/files/documentation/...) or with flash memory and RAM ICs, all packaged together in a system-in-package footprint. (e.g. https://www.espressif.com/sites/default/files/documentation/...) There are various options for which flash and RAM ICs are packaged together, but the ESP32 die itself is very much an MCU and has only has 520 KB of SRAM.

A managed switch is very computy heavy, and does usually run a microprocessor with a full RTOS, if not Linux itself, which probably costs in the mult-dollar range. It's also not something most people have at home, outside of the switch built into their router. Everything elese you mentioned usually runs on microcontrollers with under 1 MiB of RAM. For example, Infineon's CYUSB306X series ASICs for webcams come in two RAM sizes: 256 KiB or 512 KiB, despite handling gigabits per second of data, and having an MCU at all isn't even necessary. (https://www.latticesemi.com/usb3#_CDED461DE15245C78A2973D4A4...) The Pinecil's Bouffalo BL706 MCU has 123 KiB of RAM, despite being a low-volume product where design time matters more than component cost. (https://wiki.pine64.org/wiki/Pinecil, https://en.bouffalolab.com/product/?type=detail&id=8) Microwave ovens are so high volume that they often don't even use packaged microcontrollers, mounting the die directly on the PCB, with an epoxy blob protecting it, and there's no way any would splurge on megabytes of SRAM. The most advanced microwave oven I've seen was from the 90's and definitely didn't splurge on an microprocessor. (https://www.youtube.com/watch?v=UiS27feX8o0)

A slow MCU with external memory could run anything, like booting into linux on an AVR (https://www.avrfreaks.net/s/topic/a5C3l000000BrFREA0/t392375) but it's going to be extremely slow and not practical for any commercial product, which if produced in any volume will have as little RAM as possible.

[TrueDuality]

You don't necessarily need on-package RAM for this. I'm not sure I'd build a project around this, but 16MiB of RAM would hardly be BOM killer.

[PinguTS]

Actually it is. If you want to build a cheap sensor or actuator, than any additional component is getting expansive. Remember it is not only the external component, it is also the PCB space, is the production, and the testing after production. This adds up all to the costs.

When you use a µC to make it cheap, then you don't want to use additional components.

[jdndnc]

RAM on MCUs is getting cheaper by the minute.

A couple of years ago it was measured in bytes. Before the RP2040 is was measured in dozens of KiB now it's measured in MiB

While I agree that 16 MiB is on the larger side for now, it will only be a couple of years for mainstream MCUs having that amount on board

[jbarberu]

Also curious what MCUs you're working with to give you this impression?

RP2040 is 264k, RP2350 is 520k.

I use NXP's rt1060 and rt1170 for work, and they have 1M and 2M respectively, still quite far away from 16M and those are quite beefy running at 500MHz - 1GHz.

[tonyarkles]

While I generally agree with you, the RT106x line does support external SDRAM as well. I've got an MIMXRT1060-EVKB sitting here on my desk that has 32MB of SDRAM alongside the on-die 1MB of SRAM.

[theamk]

Those specs are $50 for compute module - a very non-trivial cost.

[15155]

> NXP's rt1060 and rt1170 for work

These both have FlexSPI controllers capable of interfacing with $3-5 in PSRAM at 8M or 16M.

[FirmwareBurner]

>RAM on MCUs is getting cheaper by the minute.

It really isn't. The RP2040 has 256KB RAM. Far away from 16MB.

>now it's measured in MiB

Where? Very few so far and mostly for image processing applications, and cap out at less than 8MB. And those are already bordering on SoCs instand of MCUs.

For applications where 8MB or more is needed, designers already use SoCs with external RAM chips.

>it will only be a couple of years for mainstream MCUs having that amount on board

Doubt very much. Clip it and let's see in 2 years who's right.

[pessimizer]

Bigger processors with more RAM have always been available. The question has always been whether you're going to use a $20 processor when you could do the job with a 50¢ one. It's the difference between your product being cheap and disposable, and you getting to choose your margin based on your strategy; and not being able to move a unit without losing money, hoping to sell yourself to someone who knows how to do more with less.

I'm an Erlang fanatic, and have been since forever, paid for classes when it was Erlang Training & Consulting at the center of things, flew cross-country to take them, have the t-shirt, hosted Erlang meetups myself in downtown Chicago. I'm not prototyping a microcontroller application in Erlang if I can get it done any other way. It's committing to losing from the outset.

edit: I've always been hopeful for some bare-metal implementation that would at least almost work for cheap µcs, and there have been promising attempts in the past, but they seem to have gone nowhere.

[toast0]

AtomVM runs on esp32, right? It's not an ultra-cheap microcontroller, but it's pretty cheap. AtomVM isn't BEAM either, though. I have no experience with AtomVM though... it didn't seem like a good fit when I was building something with an ESP32 (I didn't see anything about outputting to LCDs, and that was reasonable with arduino libraries... I also saw a library for calendars and thought that would work for my needs and then I got dragged into making it work better), and it would have worked for the stuff i was doing with ESP8266, but I didn't know about it when I was shopping for boards, so I didn't want to pay extra.