Memory Management Fun

Flash?

There comes a time in every programmer's life when they ask themselves, "how much memory is my code using?" Now is that time.

Background: what are we doing?

Being a first aid kid addon, the logical addition to our product is a way for people to find out first aid information in order to help people in trouble. So, of course, we decided to go and make essentially a new operating system for the Photon to run off of. What could go wrong?

C++ is Fun (this is a lie)

Though it's quite widely known and I do have a bit of experience, C++ still posed quite a few challenges in programming. To put it bluntly, I'm still working on it. The inclusion of libraries and a lot of other factors have made this project quite a bit more complicated than I would have liked, but this is the life that I've chosen.

Crashing and Memory Management

The Photon and its firmware are both quite fickle, and the slightest perturbation has caused countless crashes in our testing. Code that works fine one moment crashes the next, sometimes without any changes, though rarely in such a case. Much more common is random crashing caused by removal of code that has nothing to do with the cause of the crash!

When I was first prototyping the code, I decided to include an abbreviation field to store a menu's abbreviation. But I never used this field, and so I believed that I could free up some critical space by getting rid of this space. No dice, however, as the program crashed as soon as I pressed any buttons. No debug output could explain it; and at this point this memory-eating feature still exists.

Another fun bug came with changing the information that our device provided. I noticed that some characters were being cut off, so I decided to fix it in my code. And again, it just decided to crash randomly?

This issue is very confusing, and the only explanation I possibly have is that the method of allocating memory within the code is not allocating enough. After all, I am using an array of char pointer pointers as a 2 dimensional array, so I do not know the specifics of how the Photon manages its memory. Thus, attempting to read the memory at a certain point may exceed the bounds of the array and read other information that is complete gibberish.

But it this were the case, there still remains a puzzling bug. The location menu currently has no functionality built into its center button. In the final product, pressing the center button should call the Geolocation methods we worked so tediously on before and then display the results to the screen. But right now, we are still prototyping this "Operating System" so that functionality is not included. Despite this, pressing the button appears to be a toggle of some sort. Specifically, toggling whether some gibberish appears on the menu or not. We added tracing calls to see whether some other subclasses' method was being called instead, but it was not. The code within the method itself is just the tracing output.

Color me surprised. These random crashes happen for no apparent reason, either. It's quite frustrating trying to develop in such an environment. Perhaps it would be better to try and develop something similar for a computer instead, just to try and flesh out the concept.

Video Editing is Hard

In Our Best Interests

To not watch the proof of concept video. But if you insist, you can check it out here. Because I don't want to upload the video again.

Also it uses flash. Did we just get out of a time machine a decade in the past?

Broken Code and Broken Dreams

Push to Master

Don't do it if your code doesn't work. Please. And if someone opens an issue, please work on resolving it.

Sorry

I had to get that rant out of my system, I realize that many of these Particle library devs are volunteers who do what they do out of love. So I'd like to take a moment and that all the people working on Open Source projects right now. Y'all the real MVPs.

Cutting it Close

Our proof of concept's requirements weren't really that stringent. That being said, I did want to add as much functionality as possible. In fact, I made an entire post about getting the Geolocation to work. What didn't make the cut into the proof of concept is somewhat more interesting.

Hardware that Failed

Our Nokia 5110 LCD came with a part that we had trouble identifying at first. Turns out, it's a Texas Instruments CD4050BE, a fancy part that made wiring much trickier. In fact, we weren't entirely sure what its purpose was. With a little digging, we found out that the LCD worked just fine without this part. And sure enough, it did. So now there's a CD4050BE just sitting around in our design lab. In case anyone needs it.

The other component we were playing around with was pulsesensor.com's (appropriately enough) pulse sensor. In our demo testing of the hardware, we were able to get it working just fine. But that was 2 weeks before our proof of concept demo. We were content with it working, and so decided to move onto the LCD and Geolocation, figuring that getting the pulse sensor working would be easy enough.

Turns out, it's not that simple. In the two weeks that had passed, the author of the code released an update. Appropriately enough, our code broke. It was time to go hunting for a reason. Fortunately, Particle's online IDE's libraries make use of Github. The repository was just a click away. And checking the changelogs and the Readme gave us an answer as to why it was broken. Previous versions had included a dependency library along with the library code. The latest version separated them, so that it was necessary to include both libraries in the code.

So we went back and did that and... nothing. Instead of complaining about being unable to find a necessary library, it was complaining about an error within the library itself. Quite puzzling indeed.

We still had a working demo with example code, though. So we booted it up, and sure enough it worked just fine. It was running version 1.5.0, while the newest version was 1.5.1.. So instead of including 1.5.1 in our proof of concept code, we decided to go with 1.5.0. After all, the example code worked fine. Why wouldn't the rest of it work?

Well, for some bizarre and unknown reason, that code broke too. Same exact error as the 1.5.1 library, even though the example code worked fine. Our demo code with the 1.5.0 code still worked, and so did reusing the example code for 1.5.0. But when we tried to migrate the Pulse Sensor code to our proof of concept, it broke every single time.

At this point, we had already invested nearly an hour of time trying to get the pulse sensor to work. No matter what we tried, it simply refused to. So instead of wasting more time, we decided to cut it. For the proof of concept, we only really needed a location and a screen display that location. So we decided to work on those for a change.

Hardware that didn't quite Fail

To be quite honest, hardware and software are both hard. And for us in the Hardware IoT section that involves programming our devices, getting both to work together is even more difficult. Case in point - another many years of time used getting the screen to work. Aside from cutting out that weird Texas Instruments part, we did have to do quite a bit of work to get it working. And the other hard part about it - if it's not working 100%, it won't do anything.

Actually, that was a lie. The backlight controls and the screen control are separate. Aside from that, however, we had zero feedback as to where our errors were.

And speaking of errors, there were quite a few of them getting the screen to work. Our Photon currently has a significant amount of its pins in use just for the screen. Misplace any one of them, and the entire thing fails and nobody knows why. In fact, we broke it multiple times over the course of testing. Mostly, it was accidentally pulling out a wire. But sometimes it was trickier., We spent a good 20 minutes trying to get the screen working once, only to find out that somehow a wire had moved from A3 to A4. Resetting it quickly fixed the issue.

One Grand Realization

Experience really does matter in this line of work. There are so many different things that all have to be working in perfect harmony. Even though I have quite a bit of experience coming into this class, I've still been stuck on problems for many hours that turn out to have simple solutions. And it's not because I refuse to learn from my past mistakes. No, it's because there are so many possible mistakes to make, that it becomes impossible to not make one eventually. Even the most experienced of engineers will end up hooking up a wire incorrectly. Some may spend hours in their current state trying to diagnose the issue. Others may decided to simply tear down their machine and start over.

Sometimes I feel like I should do the latter.

Occam was Right

Overengineering at its Finest

From my time browsing the internets, I've come to hear one piece of engineering advice over and over and over again.

Don't overengineer stuff.

Well, it's kind of too late for that.

Geolocation is hard

With the work on the rest of the proof of concept going smoothly and ahead of schedule, I decided to work on something that wasn't explicitly in the proof of concept, but would be helpful for a more complete project: Geolocation.

The idea is that Geolocation provides an easy way for first responders to locate the rescuer and victims, especially in less-than-ideal situations such as earthquakes with rubble everywhere. The final product relies on a GPS module, which is built into the Particle Electron, but not the Proton. In disaster situations, GPS should be much more reliable, and it also comes with Particle's built-in library, AssetTracker. But GPS modules cost $40, which we already spent on other components. That wasn't an option, nor was throwing down $70 to buy an Electron and Particle's data plan. Instead, I decided to rely on Wifi access points and Google's Geolocation API.

Why-fi? Get it?

Well, because it was basically the only option we had. We're broke college kids who can't afford GPS. So basically, Wifi is the only option we're left with. So that's what we're gonna go with, and hope that it works.

The Quest to Query Google

It's a hard day for two of us freshies who have no experience with web APIs at all. I had to obtain an API key from Google in order to use their services. The free key allows me to make up to 50 requests per second and 2500 total requests per day. I highly doubt I will reach this limit any time soon, though for completed product it may be necessary to pay the $.50 for 1000 additional requests, up to 100,000 per day. Or maybe even upgrade to the premium plan. But, of course, it is highly doubtful that we will still be using Wifi access points to determine our location when GPS is available and much more accurate.

For the prototype, though, this is about as reliable as it gets. That presents another challenge: how to actually make a query to the service. Oh boy. Our inexperience really showed here. We ran through quite a few services to try and get this working, and ended up completely ditching all of them. Yep.

IFTTT

My first attempted solution was IFTTT - IF This Then That, a simple IoT "recipe" maker that allows certain action events to trigger certain responses, as is in the name. Particle provided a handy channel that allowed us to listen for changes in variables, function return values, events, and even the device status. I decided to start with an event listener. After all, it should be the least tedious to get working, right?

Well, there were a couple problems. The action trigger in IFTTT required that the contents were equal to some arbitrary parameter, so our solution would be impossible to implement via IFTTT's Particle Event listener. Perhaps, then, the variable solution would be better.

But by using the variable listener, the solution becomes even more convoluted. We can say that the variable value is not equal to something, but then, what is stopping IFTTT from using up all our daily allotment of API calls in the blink of an eye? If we make IFTTT respond by firing an event of to set the value of the variable back to 0, we can theoretically fix it. But then there are even more things flying around. Not good.

Not to mention that querying Google's Geolocation API and returning the result was not really easy, either. IFTTT provides the Maker channel to make web API queries, which is exactly what we were after. But with our inexperience, it quickly became obvious that this was not the solution we were after. Sure, we could get the request. But how would we listen for the response? The Maker channel required an event name, but what would that be? We were absolutely clueless (and to be fair, I still am). So we decided that IFTTT was not going to work.

Noodl

In lab on the 28th of October, Simon introduced Noodl to us, a simple-to-use (Compared to writing raw code) prototyping tool that had Javascript features built-in. So I decided to try and figure out how to get it to try and query Google's Geolocation API. But like anything, it wasn't exactly straightforward.

The example code included about a few hundred lines of unformatted Javascript code that was required in order to interact with the Particle cloud. And once that was done, it required even more work to try and get an HTTP POST request to Google's API and process the response. Needless to say, it didn't quite work out as planned.

Sure, we ended up with a nice button that said "geolocate," but that button or the Javascript couldn't do everything necessary. Which was disappointing.

Thingspeak

It was at this point that I stumbled upon a post on the Particle Forums that did about exactly what we needed it to. So I decided to look up the basis of this post was. Turns out, it was Particle's own system to create webhooks. So I booted up the tutorials they provided and followed the steps they gave.

Those steps included setting something up with Thingspeak. So I did that and ended up relaying the information from the Photon to the Particle Cloud and then finally to Thingspeak. At Thingspeak, I was successful in creating a POST request to the Geolocation API. Almost there!

The only issue now was to try and process the response. I had to create a listener for the response and then create an action handler to forward that information back to the Particle cloud. The only problem with that was, well, all of it. I didn't know how to do that whatsoever. And despite me playing around in Lab for about 2 hours to try and fix it, I couldn't get it.

Give up?

Nope. If you find yourself in a pickle, back up a few steps to try and see why you're in the pickle in the first place. So I did just that, and I realized something. I didn't need a 3rd party cloud service at all. Particle's own Webhooks were powerful and simple enough to do just what I needed. Thus, I resolved to create a Webhook that would connect the Photon to Google and get its location.

Webhooks

Finally, the solution is known. No 3rd party cloud services necessary. A simple Webhook is enough to relay all the necessary information to determine a device's location. The only issue is that the Webhook creation process wasn't exactly straightforward. Once again, I was left fiddling with the system for a while before figuring out how it worked at all. And, to be fair, I still don't understand exactly how it works.

Creating a webhook can be done in two ways. With a proper JSON file, you can do it using Particle's Command Line Interface. The web interface also works and is more user-friendly, but at the same time leaves users with so many options that they should be overwhelmed. At least I was.

What's more, webhooks currently cannot be edited. If you mess up, you have to delete it and start over again. This is an issue.

Moment of Truth

Would it even work, though? Well, as they say, there's only one way to find out.

I flashed the Photon with the firmware then went to the Particle App. Sure enough, the function scanWifiAPs showed up as a callable function.

I opened up the Serial monitor to read the data I would be receiving.

I called the function and waited.

The data in the format to send to Google showed up.

And nothing.

What have I done wrong?

Turns out that Google's Geolocation API is quite fickle. A quick check of the Logs showed the reason - Response code 400, which means that either

• My API key is faulty
• The response body is incorrect.

Except neither of those was the issue. I just called my method again, and it returned something!

Did I mess up?

I got a location at approximately 40N 80W. I plugged those numbers into Google Maps, and...

I'm in the middle of nowhere. The nearest city is Pittsburgh. Close, but not quite.

Call me insane, but I tried the exact same thing again.

Google Why

Nope, it works this time. I am now consistently placed within 40m of the middle of the Duderstadt Center, which is where I have been testing. I have no clue why any of those errors are happening. I blame Google.

Words Unspoken by any Engineer

"It works!"

Of course, all this work is only for a proof of concept at the moment. For a final product, the Particle Electron and its AssetTracker library provides easy wrappers around its built-in Adafruit GPS module, which can obtain a device's latitude and longitude with ease.