Rust on the RP2350 (2024)

https://thejpster.org.uk/blog/blog-2024-08-08/

by fanf2 • 1 year ago

148 51 1 year ago

thejpster.org.uk

sph• 1 year ago

Can anyone explain how the dual ARM/RISC-V system works, architecturally?

Are there two actual CPUs on the same die? Is it one shared architecture with two different instruction decode stages, one for ARM and the other for RISC-V that can be toggled at boot time? I like the idea conceptually but I'm not sure how much of that is a hack and/or inefficient compared to a pure ARM or RISC-V core.

dcan• 1 year ago

To be more precise, four CPUs - two ARM and two RISC. There is just a mux for the instruction and data buses - see chapter 3 of the [datasheet](https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.p...).

It’s space-inefficient as half of the CPUs are shutdown, but architecturally it’s all on the same bus.

Narishma• 1 year ago

It may be technically space inefficient but they only added the RISC-V cores because they had area to spare. It didn't cost them much.

myrmidon2• 1 year ago

I find this whole concept remarkable, and somewhat puzzling.

Have seen the same (ARM + RISC-V cores) even at larger scales before (Milk-V Duo @1GHz-ish). But how is this economical? Is die space that cheap? Could you not market the same thing as quadcore with just minor design changes, or would that be too hard because of power budget/bus bandwidth reasons?

Aurornis• 1 year ago

It’s space-inefficient as half of the CPUs are shutdown

In practice is doesn't matter very much for a design like this. The size is already limited to a certain minimum to provide enough perimeter area to provide wire bonding area for all of the pins, so they can fill up the middle with whatever they want.

MisterTea3• 1 year ago

Can anyone explain how the dual ARM/RISC-V system works, architecturally?

What I really want to know is why would anyone need or want dual architectures on one chip?

pjc502• 1 year ago

This is hedging their bets.

Tapeouts are expensive. It seems that they had spare area, so they decided to add RISC-V as a sort of feature test and market test; that lets them determine what the market preference is between the two and acquire geek coolness points (plus an additional point for using Rust) at relatively low cost, certainly lower cost than doing two tapeouts for two different SKUs.

Here at $MEDIUM_SIZED_CHIP_CO, we also have some products which have a custom DSP for realtime audio processing and an ARM for "other stuff". It's more common than you think. Even the very first Pi was effectively a video-oriented vector processor with a small ARM glued on the side.

cmrdporcupine• 1 year ago

Isn't half the mission of the Pi project that it is an educational project, and also taretting hobbyists?

In that respect it makes perfect sense to me.

password4321• 1 year ago

Which of the four RP2350 variants is used in the Raspberry Pi Pico 2 W? I see RP2350A0A2⁰ and (pardon my ignorance) guess that means SKU RP2350A package QFN60, the one with the least features.

⁰ https://datasheets.raspberrypi.com/picow/pico-2-w-schematic....

moefh• 1 year ago

As far as I know, any Pico 2 currently sold carry the RP2350A: 30 GPIOs, no internal flash since the board carries an external flash chip.

(BTW two of the variants are called RP2354 and not RP2350, the last digit means the amount of internal flash)

maeln• 1 year ago

Most picture I find seem to show the RP2350A variant for the W and non-W version.

teleforce• 1 year ago

Previous post on HN:

Raspberry Pi Showcases Rust on the RP2350 Microcontroller (9 comments):

https://news.ycombinator.com/item?id=41476505

mastax• 1 year ago

thejpster, where do I know that username from...

Ah, he wrote most of embedded-sdmmc-rs which I used quite a bit. Jonathan, if you see this, thanks!

drrotmos3• 1 year ago

Note that this was written 2024-08-08. While I haven't kept up to date with exactly what's been happening in rp-rs, I do know that probe-rs has since been updated with support for the RP2350. Other things may be outdated as well.

jayyhu• 1 year ago

The author points out that his changes have already been upstreamed to https://github.com/rp-rs/rp-hal

moffkalast• 1 year ago

See, this is why we use conformal coating ;)

GolDDranks• 1 year ago

I own a home router (TP-Link Archer C7) and I have been running OpenWRT for many years on it, having full control over it via SSH. A few years back, I had an idea for an daemon process/service to improve a certain thing in its functionality. I was delighted to find out that the MIPS chip that powers the thing was supported by Rust, and I coded a "script", cross-compiled it to a binary and SCP't that to the router. It ran beautifully. After that (and running Rust on a few other embedded systems, including an ARM Cortex-R chip) I became convinced that Rust is the next C for the embedded.

johnisgood2• 1 year ago

I became convinced that Rust is the next C for the embedded.

Ada works, too, though, or Forth. :P

johnisgood2• 1 year ago

See more at https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Dev....

ricudis• 1 year ago

The OpenWRT SDK is quite polished and convenient to use, so I usually use that for custom OpenWRT binaries. But a few days ago I needed to run something custom on my old QNAP NAS (Marvell ARMv5TE based), and I decided to try cross-rs[1] for the first time.

It turned the usual multi-hour expedition of locating and configuring SDKs, toolchains, etc into 3 commands and 5 minutes of downloads and compilation. The resulting executable ran successfully at the first try. I was amazed.

[1] https://github.com/cross-rs/cross

overfeed• 1 year ago

I default to Go for code I want to run on old MIPS and ARMv5/v6 appliances because despite the "huge" binary sizes, cross-compiling is done by setting 2 environmental variables.

boguscoder• 1 year ago

Embassy got _some_ support for rp2350 for quite some time now

https://github.com/embassy-rs/embassy

drrotmos3• 1 year ago

I'm very much looking forward to giving Embassy on the RP2350 a go. I've been using it for a while with the RP2040, and it's a joy to use.

vkaku• 1 year ago

Uhm, I was looking to try it and I found this advisory: https://forums.pimoroni.com/t/rp2350-gpio-internal-pull-prob...

Would suggest people understand this before buying.

Rust on the RP2350 (2024)

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