Thanks!

You might want to check out the Kendryte K210. I'm trying out these boards for development. They are designed with two (I think) 64-bit RISC-V cores with a hardware FPU. https://www.seeedstudio.com/blog/2019/09/12/get-started-with...

I've flashed mine a few times, but I'm still working to getting it to work. The documentation isn't very good, so I'm working to reverse engineer some aspects of it.

This is a low cost alternative. Of course, we could go with the SiFive Unleashed (64-bit) or the SiFive HiFive1, which uses a 32-bit RISC-V CPU in an Arduino form factor. https://www.sifive.com/boards

The SiFive Unleashed cost me a cool $1k, so I'm still scared to mess with it.

The Kendryte is pretty limited in many ways, not least that it's permanently limited to 8 MiB of DRAM (AFAIK).

The most interesting route is using an FPGA. There are many examples of running RISC-V softcores on FPGAs (for example, Berkeley's RocketChip) and many boards that support a decent amount of memory (even beyond 1 GiB).

I tried some of SiFive's evaluation cores. They limit you quite a bit unless you pay. Furthermore, many of the FPGAs worth their salt were quite expensive. The K210 in the MaixBit form is only $20, and it comes with a camera and LCD. For hobbyists, I think it's a good compromise.

I looked at the Xilinx FPGAs--the ones SiFive recommends, but they're quite pricey.

Which FPGAs had you had luck with?

I haven't used them myself, but these boards look awesome, and they are supported by an end-to-end open source toolchain:

1. https://www.crowdsupply.com/1bitsquared/icebreaker-fpga 2. https://www.crowdsupply.com/radiona/ulx3s 3. https://groupgets.com/campaigns/710-orangecrab

I was looking at getting this Maixduino kit since it appears to be the cheapest solution that satisfies my constraints (RISCV core + WiFi):

https://www.seeedstudio.com/Sipeed-Maixduino-Kit-for-RISC-V-...

I'm not sure what's the status of programming these from Rust. I suppose that you will probably need to build your own toolchain that links the Seeedstudio libraries.

RISC-V has their own supported toolchain. You can get it here: https://github.com/riscv/riscv-gnu-toolchain.git

With Rust, you can do what I did with my OS. It can compile out of the box. The kendryte has a "BSP" (base support package) that is essentially a minimal OS, but it is written in C.

Yeah, I was thinking more about what to do with the OS afterwards. That board has lots of things on it, including wifi, so I'll probably would like to use some of that.

It would be unfortunate to have to re-implement the wifi driver in Rust, but I suppose I'll just have to link parts of the C toolchain instead, creating Rust wrappers, etc.

Well, FPGA are more flexible but cost more than a cheap microcontroller that is true. There are way too many good options, but to pick one with a fantastic community: ULX3S

Have you checked out SiFive’s HiFive1?[0] It’s an Arduino Uno sized board, but instead of a weak ATMega328p, it’s a (relatively) powerful RISC-V processor. It also has a BT and Wi-Fi chip.

[0]: https://www.sifive.com/boards/hifive1-rev-b

No need to wait, the ESP32-S2 has a RISC-V as its low-power core.

ESP32-S2 has two ULP co-processors, with one based on RISCV instruction set architecture (ULP-RISCV) and the other on finite state machine (ULP-FSM).

ULP-RISCV has the following features:

    support for IMC instruction set
    thirty-two 32-bit general-purpose registers
    32-bit multiplier and divider
    support for interrupts
    boot by the CPU, its dedicated timer, or RTC GPIO

https://www.espressif.com/sites/default/files/documentation/...

Interesting, wasn't aware. Is the ULP-FSM the same as the one in the original ESP32? I thought that one was programmable / Turing-complete, so not just a FSM?

I have never used the ULP-FSM, the new docs for ESP32-S2 are fascinating. My S2 is on its way, I don't yet have the hardware in hand.