Rust Programming Language PDXRust, 7 Oct 2016

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From YouTube: PDXRust October 2016: PSAS Flight Controller

Description

PDXRust: Capstone team who built flight controller in Rust shares their work

More on http://www.meetup.com/PDXRust/events/234601233/

Help us caption & translate this video!

http://amara.org/v/2Fi2/

A

So welcome the PFAs flight controller team to pdx rest.

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My name is Brian and I am here to talk about the Portland State capstone project. For the cs group, we did a project for peace, s I'm getting a whole what that means in a minute, just let every let everybody know every time.

C

B

Talk it seems to be a while, since the last time I've talked so I'm gonna triple over a bunch of words, so I apologize ahead of time for that, but.

D

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Ahead and get right.

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Into it, so let's start off with what is a capstone, so a capstone is a group project can be a.

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Good project based.

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On our field of studies of computer science, in our case we did this out of Portland State University with sponsors from outside of the class, so somebody from sometimes within the organization, sometimes within psu, but oftentimes outside of the school altogether, will come in and they.

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Want to build something awesome.

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They want, they need a tool, build, they need to expand some features on another product and they.

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Come in with a.

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Specification and an idea in mind and our.

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Job is to build.

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Whatever they want it, but really go through the formal process of all the software engineering steps in all of the software methodology that one might theoretically use in the real world. So who is PSS? Pss is the program state, aerospace society and they are a team of students that build rockets which.

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Is pretty cool? You don't usually get.

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To say at a student level that you build rockets, are you work on rockets? They.

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Do this at a very.

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Low cost they have to do things like build their own wife by because they can't afford GPS the type of GPS that would go into commercial grade. Rockets all.

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Is open source online as well as all of our hardware designs? So if you're following piece s, you can go on see how they've built everything, and if you have the money, actually build. One yourself which is kind of cool and the their eventual goal is to put a satellite into orbit, which is a very tall order. It's definitely not something that you do overnight.

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So p. Sas has a challenge, and this is what they came to the capstone with they want to be able to fly in space. All of their previous rockets flew in the atmosphere, and you can use fins for that or wings.

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Anything that you know works in the atmosphere and space. None of that works, so they needed to rebuild a flight controller.

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They had enough changes, they wanted to make date decided they wanted to rebuild it, but they also had enough changes in this language called breast was coming along. They wanted to try that out so.

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What does this new flight.

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Control I need it needed to use coal ship coal gas jets. It also.

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To be testable so that they can run tests on laptops instead of constantly using rockets to test sort of flight mode, it needs to be fast. It also needs to be safe. You don't want your code crashing in the middle of the flight or when it's trying to make a turn or doing something critical. So the decision that piece asked mate was that they were going to use this product called JSP sim to simulate.

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On the laptop so that they can do mimic mimicked flights without ever having to take off to be fast and safe, they decided to use the breast language and they needed to be able to read and write for these cold gas jets. Using these libraries called aight to see and gpio, which we'll talk a little bit more about later.

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So these tools.

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Were complicated we.

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Are all undergraduate we're all undergraduate, CS majors? We didn't know how to use these tools. We didn't know a lot about hardware. Some.

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Of our group members.

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Had a little bit of experience in that actually because they worked in the field before coming back to school, so we had a lot to catch up on. We had a lot to learn before even writing. The first bit of rust code, including living rust itself I, had.

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Bit of familiarity.

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Before we started and I think one other group member might have heard of it so.

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It was a new unless language.

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That we actually had to learn that from this from scratch, so we built the Minimum Viable Product that compiles in flight mode in test mode I'll talk about why that needed to happen in a second. It integrates.

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Two libraries and it integrates with the simulation software JSP sim, so to test it, we were given an LED prototype which has some videos about and integrating with JSP soon we were able to test our flight move or a test mode locally on a laptop. So let's talk a little bit, let's go into pieces, so this is PSS his most recent launch and launch it's one of my favorite videos or launch 12. So this is what the current rocket looks like.

B

As you can see, it's got spins. It's doing a little tail spin thing which we can talk about later and overall, it seems to go off without a hitch. This launch shouldn't have any problems. Oh that's true. If we want two blocks all the way until the camera falls out actually.

B

Yeah, there's actually old link to all their YouTube videos, there's quite a few just on this launch and if you get motion sick from watching videos know the time you look away all pops it right there, so they have this prototype system and I would have loved to say that we got a chance to run on this, but it by the time we were done with a code. It actually had some repairs. It needed to happen, so we couldn't actually run on this at the time.

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I have videos of the LED prototype I ran on, but this is sort of the future, but their future rockets going to look like up here. We have they have these things. These little rocket, nozzles, shooting cold gas jets out. We've got the compressed air down here, and this.

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Is a prototype they built, they.

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Wrote this in Python and all it does is keep rotations stable, and this is sort of what we had to mimic in rust. Using all these other libraries.

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So, like I said, I really wish you could have run on it, but we did not get the chance so jumping into he. I shall do this with a mouse jumping into the folder breakdown. We have our common inside of our main source folder. We have a common folder, a flight mode folder and a test mode folder. So one of the primary requirements was that PSS wanted to be able to compile the flight mode and test mode targets independently, because they didn't want some sophomore trigger to, like accidentally turn the flight mode.

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While the rocket was flying into test mode, stop working on the rocket itself and started producing JS be sent output while in flight. So.

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At compile time, they.

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Wanted to make sure absolutely that they were not going to run Jace besom code. The easiest way to do this. It's.

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Not the only way to.

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Do it the easiest way to do this was to break down flight mode and test mode specific code into their own directories below or common directory, or actually next to the comment directory and then have it referenced the common directory for the main program, the main flight software and actually data for matter as well. We needed to work with custom UDP packets that piece ass had designed so that we can send it to limit Raider back down to the ground. We need to do this because this is part of I'm referencing Jamie vector.

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This is part of the it's too expensive to buy commercial gps's for rockets. So you have to build your.

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I'm, sorry, that was separate I.

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Yeah, there's limited bandwidth that we have available for sending telemetry to the ground and we have a lot we want to get sent down to the ground. So we devised a custom lightweight binary protocol, specifically.

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We needed to send ok, I, remember Lana,.

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So let's go ahead and jump into some interesting statistics about our code. There is 651 lines of actual dress code, so that doesn't include white space or comments or anything all together combine those a thousand lines. There's forty three lines of C++ and I said CPP, because the software.

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Was using to make this presentation didn't like.

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Two plus signs together it just sort of deleted the slide it seeming me instead and.

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This is mostly because we had.

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To talk two jsb sin, which isn't entirely, which is entirely written in C++, it also has 668 lines of markdown documentation, which.

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A slightly more documentation than we have code, some.

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Of it is useful, some.

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Of it was really just a jump through hoops for the capstone project, so some interesting problems that we had when working on this jsb sim is a really hard tool that work with it's virtually undocumented. As I said, it was written in C++ and it kind of has spaghetti code. I had.

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Two people working on just this piece of it and it took the entire six months.

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Of our project.

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Come up with the perfect concept that we needed build an actual, testable runnable simulation, really really. A pain in the button are compiling.

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Modes, the way we solve that as I previously stated- probably wasn't the only way to solve it as probably other ways to do that too. But this is the one that we found was the easiest to do it didn't require building make files it didn't require. You know any code configuration it.

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You to be in the right directory when you compiled at the right time so.

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It seems like the simplest.

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Way to to do it, but it's certainly not the only way, some interesting bugs that we came across two bugs and I had two videos to show you so our counter clockwise bias, which was the fact that the LED board, based on temperature and slight variations of where it might be sitting in on the axis at any point in time. It's zero point wasn't actually zero, and then we actually had a dual spin bug I'm going to show both of these off.

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So this first book was I should probably explain this a little bit, so the rate of LED blinking was just set on a timer. So if we detected that we had, you know a plus blink green, we.

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The Midas blink red and it blinks in the opposite direction that the rocket, if you can imagine this being a piece of a rocket sort of lengthwise where the cold gas jets would light up. The cool gifts just would accelerate in the direction that the lights were going in the opposite of the direction. Well,.

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You'll notice here is that the.

B

Mm I did not actually get on the Wi-Fi. Can we pause this really quick.

B

Sorry about that, so you'll notice that I think we have a bias in the red direction. Red is blinking, nice and consistently. Green is blinking, but it kind of doesn't link all the time. So we have a bias which means that the center of this rocket is not actually the center. Once we fix that code, we you can see here, then that binds it seems to be working. Fine. We fixed this a couple of different ways: the.

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First way to fix.

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This was just to manually input. What we saw was the average bias and that got us going along for a little while and then later we actually wrote the rewrote that piece of the program to find an average of what the rocket was or.

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What the gyroscope was reading.

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Said that is a bias and applied. That's all of our readings and that.

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Worked out much better.

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And works even if there's a big enough change, that your biases isn't consistent. The next book we come across we came across. Was this duel spin bug? If you sort of trick.

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Controller back and forth, you can get both lights to go on at the same time, which you can see right there, and that should never happen. So if the rocket is experiencing some sort of jiggle and both of them are going off at the same time, it's not doing anything productive, it's wasting gas, but it's also potentially just going to throw your rocket out of whack. We did end up fixing that bug, and this is actually what it looks like so to actually explain here. We first run the program.

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It takes a couple of seconds to figure out what that biases and then it starts running and it just dumps to the screen all the all of the gyro data, then we're going to do a little back and forth on the prototype. So the prototype is going to show its red and green lights and then.

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We're going to come.

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Back to the screen, where we've loaded up the telemetry viewer, which is that the UDP packets and you can see that it's working.

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Was our final product.

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That took about six months to do, of course,.

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Account that we all had to learn rust.

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All of these libraries and a bunch of mechanical work, but we feel pretty good about it and we're pretty happy that we got to that stage. Oh.

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And that was the watch at work slide already did that so code time. So let's go ahead and jump into what the code actually looks like, and now these microphones make more sense to use so over. On the left side. Here we have the common directory, the flight mode directory and the test mode directory. Now the files I showed you before was just a subset of the files. There's a whole lot more in here, for example, all of our JSP sim integration stuff. All of these work off of you XML, but it's an old program.

B

That is what it is. We have some see make files in here we have some c++ wrapper files to get we needed to use. We needed to run the rust code that will actually run C++ code in order to go all the way down to JSP sim. We actually had to write a rust wrapper and, as you can see, I didn't actually write this or else all of the line. Endings would not be showing. Oh.

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That's actually a good point. Sorry about that.

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Yeah that'll work.

D

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Thank you. So we have a rust wrapper that calls C++ wrappers and that is below are rust code and above the JSP send code. So it takes a little bit to get j's PCM integrated with rust, but fortunately we actually we're able to do it. I to see in gpio I'm not going to dive into too much, because I don't have enough time to talk about deeply what they are, but we basically had to wrap them up in our own rusts trucks and call them internally in flight mode.

B

So the best way to explain this is the common code, which is like, where our main program is, is going to load up these I to see and gpio interfaces and start talking to them, but in our flight mode we need them to talk to hardware and in test mode. We need them to interact with JSP sim. So we had to write wrappers between those and on the JSP sim side. We had to write the rest in the c++ rapper, but we had to write our own modules in between those that had consistent.

B

For example, implementations on those trucks functions that we implemented ourselves. So, for example, we have in flight mode gpio. We have a my pens, struct and in the test mode gpio we have the pipe instruct and this only works because we're compiling them to different one of these gpios is being compiled at a time or else we'd have similar conflicts and we didn't do anything super crazy. With our rust pode, we tried to keep it pretty simple. That's also pretty much.

B

The only rest we knew we I was I was actually pretty happy that I got the team to use results and options instead of just returning integers that had error codes attached to them like you would do in see. A couple of our programmers were old-school seat programmers, so they sort of mimicked what they were doing on the seaside, which isn't really idiomatic rust. It works, but I wanted to get everybody to use the correct sort of idiomatic way of doing things.

B

There's a lot of code to go through, like I, said, there's over 600 lines, so I'm not gonna be able to touch all of it. But this is all on github there and the rocket videos I showed you were there and I. Think I am ready for questions.

C

So we are recording, so I will pass you a mic. If you have questions, I.

C

Did you consider so you had some kind of like duplicated types for one for the test and then one for the real thing. Did you consider putting all of that into a trait and and then just requiring having a common code requires something that implements the trait you.

B

Started talking about trades and how to implement those, and at the time that we were designing it, we didn't know enough about trades when we prefer speaking looking back on it. I probably would have done something like that. I would have designed it with more of a trade system, but we still needed to keep our code separate, or else we needed some really complicated make file to make it all work. So we still.

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Kind of needed to.

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Implement everything twice on the Sun level.

A

Oh ma, I'm not terribly familiar with rest, but is there any like checks for integer, overflow and underflow.

B

Your overflow and underflow, I I'm not actually sure about that I haven't written rest in a little while that's true life cycle, haha the.

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Tldr is by default in debug mode. It will check and not release mode, but then there are options to change that or to use it in specific cases.

C

Okay, any other questions for the flight control team. I.

B

Really wish, I could actually show you she, you would actually work on this laptop, but this is not the laptop I developed on. This is my work laptop and it was just last minute my laptop wasn't working properly, but you did get all of it to run. I have the videos of it and so long as you have JSP sim installed properly. You can actually get this.

C

That's well. Thank you very much. Brian thank.

B