Raspberry Pi Bare Metal Programming with Rust

https://blog.thiago.me/raspberry-pi-bare-metal-programming-with-rust/

by thiagopnts • 11 years ago

340 88 11 years ago

blog.thiago.me

kalimatas• 11 years ago

Thanks for sharing!

s986s• 11 years ago

Very cool! Rust has been impressing me alot these past few months.

nickysielicki• 11 years ago

I remember reading a couple months ago that bare metal using Rust was in a bad state. If I recall correctly the outputs were prohibitively large, among other issues.

Has that changed?

steveklabnik3• 11 years ago

The real reason that Rust isn't necessarily wonderful for bare metal is that a lot of the things you need to do aren't stable yet.

Binary size isn't a problem, though. A lot of the threads talking about sizes aren't doing all the stuff you need to get truly small binaries. That's because, as this stuff is on nightly, it has much worse (or no) docs, so it's easy to miss things.

I'm working on a little kernel, the one linked in the first line of the post, and it's great.

Aeolos4• 11 years ago

I have the perfect project for this! Generate a signal using the GPIO ports to drive a mirror and camera in a synchronized fashion.

Does anyone know if the RPi GPIOs can be driven at around 80KHz? I've seen reports that this is possible, but that the USB or video driver tends to lock the CPU for long times, messing with timings - but hopefully running on bare metal would take care of that.

asandweech• 11 years ago

This might be of interest: http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-...

Aeolos4• 11 years ago

Excellent, thanks!

So GPIO performance won't be a problem, but they note that OS multitasking can cause issues:

"What is not evident from the snapshots, however, is that due to multitasking nature of Linux, the GPIO manipulation is constantly interrupted for short periods when the CPU is doing something else, such as receiving or sending data over network, writing log files, etc"

Running on bare metal should take care of that, so the only remaining problem is how to synchronize the signal generation on the RPi with the recording of data on the host computer. (Sigh, if only RPi had a USB3 port...)

jcoffland4• 11 years ago

You could do this with much less than an RPi. I would recommend using an AVR or better yet a 555 timer if all you need is an 80KHz signal. Let me know if you want help with this I'm looking for projects like this or something much more complicated.

IshKebab• 11 years ago

I wouldn't recommend an AVR. That is outdated technology. Even Atmel mostly makes ARM microcontrollers now (and they are much nicer than their AVR ones).

cmrdporcupine• 11 years ago

Or a Parallax Propeller

Aeolos4• 11 years ago

That's true, the reason I mentioned the RPi was because I happen to have one lying around. (Actually, I seem to remember there are a couple of AVR development boards lying around in the lab, so these might be worth a look.)

My project involves generating two analogue signals to drive a mirror (a sin wave on the x-axis and a staircase pattern on the y-axis), and a synchronized digital trigger signal for the camera. There are a number of configuration options that make this slightly more interesting than it looks at first (frequency, number of sin periods per staircase step, duty cycle and number of triggers per sin).

An implementation of this on a NI DAQ took the better part of a day and an implementation on a FPGA took roughly two weeks (mostly spent on familiarizing with the tools and communicating settings from the host.) I actually think an implementation on the RPi would be simpler than either, including wiring up simple DAQ.

tdicola• 11 years ago

Yeah 80khz should be no problem. Even in Linux if you access the Pi's GPIO registers directly you can toggle pins in a tight loop at around 1-2mhz. As others mentioned though you might look at a small microcontroller though since the Pi is kind of overkill for generating a simple signal.

bsder2• 11 years ago

Even in Linux if you access the Pi's GPIO registers directly you can toggle pins in a tight loop at around 1-2mhz.

Careful, this is strongly dependent upon the hardware, not Linux.

I seem to recall that people doing SWD programming can barely get the GPIO's to move faster than a couple of KHz.

I can tell you that, at least on the BeagleBone Black, you have to do some Linux driver voodoo to get better than a couple of KHz.

Edit: I stand corrected. Apparently the Broadcom chip in the RPi does much better than the TI one in the BeagleBone Black when driving baseline GPIO's.

niccl2• 11 years ago

And then if you want to get seriously weird, you could try the PRU on a Beaglebone Black. Two internal processors (almost) entirely separate from the main processor. They have a 200 MHz clock speed and can generate extremely accurate and deterministic time critical signals

rdtsc• 11 years ago

Here is an example of a project driving a realtime camera with Beaglebone black.

http://www.erlang-factory.com/static/upload/media/1394631509...

There is a video for the presentation as well.

https://www.youtube.com/watch?v=OBGqVmzuDQg&list=UUKrD_GYN3i...

The trick is Bealgebone black has 2 co-processors PRUs and they can be used for realtime work:

http://beagleboard.org/pru

http://elinux.org/Ti_AM33XX_PRUSSv2

It is a programmable 200-MHz, 32-bit processor with single-cycle I/O so it can be used to toggling GPIO pins.

akerro2• 11 years ago

Is Rust the future? As a C++ (hobby), Java (full time) developer, should I invest my time in Rust?

jacquesm2• 11 years ago

Rust, Go, Java, Scala, Clojure, Javascript... (leaving out quite a few other choices for brevity). They say choice is a good thing but too much choice is actually really annoying and fragments the community across a very large number of ecosystems.

akerro2• 11 years ago

I can't stand JS and Go syntax, I tried a few times... This is the worst thing that happened to humanity after in XXI century. I feel more comfortable with Prolog than with JS.

pdpi• 11 years ago

I see the point you're trying to make, yet:

- Nobody in their right mind would choose Rust or Javascript for a project where the other is more appropriate.

Though (AFAIK) Scala and Clojure both interop quite well with Java, and Scala/Clojure interop isn't terrible either, plus there's definitely a culture of reusing in Clojure/Scala all the stuff that the Java ecosystem already had. So this cluster isn't causing much fragmentation at all.

You have something of an argument that Go and the JVM languages clash for mindshare, but at that point the argument around really annoying fragmentation has kind of lost steam.

Cshelton• 11 years ago

Out of all the new languages of the last 5 years or so (D, Rust, Crystal, Go?, etc.) I think Rust shows the most promise. It is attracting both c/c++ people and people coming from dynamic languages (Python, ruby, js). So I'd recommend trying Rust out for sure, not much to lose, maybe spending a day...

vive-la-liberte• 11 years ago

The first release of D was in 2001. That's 15, not 5, years ago.

craftkiller• 11 years ago

If you're just concerned about employment then you'll probably be fine with java (maybe go in the future). If you're looking for self-improvement then its always a good idea to learn a new language, especially if it does something different like Rust's borrow checker. Outside of that, I also used to do all my hobby code in C++ and after learning Rust I'm never going back to C++.

pearjuice• 11 years ago

maybe go in the future

Go is not going to replace Java in the future. For a language which cannot even lock dependencies to a version, people sure like to pretend it is the holy grail because Google made it.

magicmu3• 11 years ago

I started playing around with Rust a few weeks ago and fell in love; it has some quirks for sure (the whole borrowing system is a bit tough to grok at first) but it didn't take long for me to start seeing things the "Rust way." My only hang-up with it right now is that so many of the most useful packages in Cargo depend on the nightly build of Rust.

Manishearth4• 11 years ago

Could you list which packages you tried to use which were blocked on a nightly? In many cases a package can be moved off nightly with trivial changes, I can try to do it.

buster• 11 years ago

I think you should lean Rust just for some new insights and patterns (error handling, optionals, pattern matching come to mind). It might make you a better programmer over all.

zokier2• 11 years ago

As a fan of Rust I don't think it is really going to be the future. While it might be successful in its own way I now believe that it will remain relatively small-scale (compared to e.g. C++ and Java). The entrenched players are extremely entrenched and Rust lacks the mass appeal that popular languages such as Ruby and Go have, being more complex to learn and write.

EugeneOZ• 11 years ago

If you invest your time in reading books then with same success (at least) you can invest your time in Rust. And there are chances it will be even more useful.

Animats2• 11 years ago

Very nice. A few more months and that should be stable.

jcoffland4• 11 years ago

As a long time C programmer this is not very convincing. A C program to do the same requires far less voodoo. All you need to do is take the address of the GPIO register then toggle the bit. No name mangling. No error handlers to override. Don't get me wrong I know rust does have some compelling features. It does seem odd to me that so many of what would be compiler options in C are hard coded.

steveklabnik3• 11 years ago

We generally try to put options in source code or configuration files, rather than in command-line flags, because that's more repeatable. It makes the CLI much simpler.

izacus• 11 years ago

Of course that same ability lets you clobber anything else in your address space and leads to those lovely debugging sessions playing "track down what corrupted my datastructure".

Manishearth4• 11 years ago

Whilst having to debug this is still undesirable, I recommend trying `rr` (http://rr-project.org/) to track this if you're ever in such a situation. It's as simple as setting a watchpoint and reverse-continue-ing!

I don't do much C/++ these days, but when I do (and it's a large codebase which is hard to debug), `rr` is invaluable. It works with Rust too.

hatsunearu• 11 years ago

As the author said at the end, the general "good practice" for Rust is to encapsulate the weird stuff and unsafe blocks into a safe lib that other people can use.

pcwalton3• 11 years ago

Point by point:

All you need to do is take the address of the GPIO register then toggle the bit.

Yes, and that is unsafe. Rust makes you put that in an unsafe block, to encourage you to build safe interfaces. This is a good thing.

No name mangling.

The alternative to name mangling is not having a module system, with all the fun name conflict issues that come with it. Rust made the right decision here.

No error handlers to override.

C has no concept of a panic handler because what would be panics in C are undefined behavior. Undefined behavior is bad for safety and understandability of the code. Having to declare an error handler is a small price to pay.

It does seem odd to me that so many of what would be compiler options in C are hard coded.

Because Rust is safe by default. That's one of its most important features. Being more like C in the ways you mention would mean compromising that principle.

jeffreyrogers• 11 years ago

After having played around with Rust a bit and seeing it used in some non-trivial applications I've grown to like it a lot, despite being an initial skeptic. However it's aggravating that in every post about Rust which raises valid criticisms about the language (in this case having to do with the ease with which C allows you to do low level programming), those associated with the Rust project leap to its defense and suggest that Rust's decisions are right for every situation.

Just because Rust can't easily do things that C can doesn't make it a bad language, but it does mean that, shockingly, there are somethings that Rust isn't as well positioned for as other languages are.

Similarly, there are things that C is bad at. Both at the high level and the low level. At the low level it hides too much of the CPU's features so for some very low level programming you need to drop to assembly. At the high level it has obvious deficiencies, many of which Rust addresses, but for interfacing with the actual hardware it is tough to beat C in terms of convenience.

Animats2• 11 years ago

That's because there's no language syntax for device address space. Modula had DEVICE as a keyword, and you could define structures as being in device space.

That's a useful language feature for low-level programming. It tells the compiler that the address space is special - it can change without help from the program. Other features of device space can include that the write width can matter (some registers have to be written as a single byte, world, or double word) and some registers are read-only or write-only. The compiler needs to know this stuff. Especially because Rust makes some strong assumptions about memory.

Rust probably needs to know about both device registers and memory shared with peripherals to operate at this level. For the blinky light program it doesn't matter; for the network stack it matters a lot.

0xcde4c3db• 11 years ago

My experience doing this sort of stuff in C is that this class of complexities is still present, but hidden outside the source in the crt0 and build scripts. Putting it in the actual program text seems like an improvement.

e12e3• 11 years ago

Exactly. I saw the gp comment and feared there was lots of boilerplate, arcane incantations -- and the only slightly smelly thing in the (IMNHO) beautiful and short example is the use of an empty asm block to "fight" the compiler on optimizing out the busy loop.

I can't imagine the full C example for this is any prettier or easier to follow?

[ed: As for "no name mangling" - having such an easy way to turn it off when needed, and yet avoid collisions when you do need it seems pretty good to me. Perhaps just having something that's "extern" be umangled by default would be better -- but it's not like one needs to bend over backwards to get a "mostly safe" bare metal program here.]

notabot3• 11 years ago

As a C programmer who fiddles with low level stuff I wonder why people get exciting about such trivial thing.

Don't get me wrong. Rust is an interesting language. The thing described in this post is well within its capability, i.e. IMO there isn't really anything that worths bragging about. Such trivial thing neither demonstrates the real potential of Rust, nor answers important questions from real world engineering perspective.

I'm all for having better tool to write low level stuff. I have dabbled with Rust and the experience was eye-opening. I think Rust still have a lot to catch up though.

rdc12• 11 years ago

Has hello world ever been exciting, it is only really a building point. You can't do anything intersting until you know the basics, of building and flashing the board.

The question is what does Rust have to offer as your embedded program grows.

notabot3• 11 years ago

Has hello world ever been exciting

The HN upvote says otherwise. :-)

But I guess had there been an HN-equivalent in assembly age people would get excited about C, too.

The question is what does Rust have to offer as your embedded program grows.

Exactly.

We are aware of the good, bad and ugly bits of C. The industry has built extensive tooling around it. Rust has a long way to go. I certainly wish to see more pioneering projects from Rust.

Manishearth4• 11 years ago

I don't think the post is bragging about this. It's well known amongst the Rust community that this stuff is pretty easy to do)

I read it as a primer for writing simple Rust programs that can run baremetal on the Pi (I've cross compiled for a Pi-with-OS before but never tried this) and access GPIO.

If you're talking about the HN upvotes, HN just tends to upvote posts mentioning Rust a lot :)

Have you looked at https://zinc.rs/?

notabot3• 11 years ago

zinc.rc is certainly interesting. Thanks for sharing!

akhilcacharya2• 11 years ago

Outside of C, are there any other languages or platforms that can do this? I'd like something modern, but I haven't liked what I've seen with Rust personally.

pjmlp9• 11 years ago

Still alive: Ada, SPARK, ATS, FreePascal, D

Controversial: Go (if someone ports the runtime to bare metal), embedded JVMs, embedded, Swift (depending how Apple drives it), .NET Native (if C# gets missing features from System C#)

Faded away: Algol, PL/I, CPL, Mesa, Modula-2, Modula-2+, Modula-3, Oberon, Oberon-2, Active Oberon, Component Pascal, Turbo Pascal, Forth, Sing#, System C#

jeremyjh2• 11 years ago

I think he was asking which languages could actually be used to do this today, without writing a new cross-compiler first.

dom96• 11 years ago

Don't forget to add Nim to that list! One of Nim's defining features (compilation to C) makes it work rather well for this sort of thing.

e12e3• 11 years ago

And C++, surely? (Although, I would probably choose C (or even assembler) over C++ for something this simple (loop, blink a light). And between all those, I think Rust is really interesting.

It could probably be argued that Rust doesn't add much on top of D (as a "better" C++) -- but between the mind-share and the focus on "safe" (and boxing in unsafe) memory access, I think Rust is really interesting. Not sure how run-time free D is coming along - believe there were some issues with the standard lib?

Ada was troubled by a confusing split between FSF LGPL Gnat trailing Ada Core GPL/commercial compiler with a release -- leaving people a little confused if there was a good Free Ada compiler that could be used for commercial (or just non-GPL) development. (Yes, it was a real issue, just as one needs an LGPL libc for c development etc).

But as I understand it the GNAT compiler has matured to the point that one can now use modern Ada without having to worry about that. Unfortunately Ada probably lost a lot of potential developers due to the confusion/issue.

kod• 11 years ago

If you want to play around with the code in this post that requires nightly, multirust makes it much more pleasant to use nightly and / or stable rust.

https://github.com/brson/multirust

Raspberry Pi Bare Metal Programming with Rust

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