We Done?

We've reached an unfortunate point now. Lab is over, and soon the entire semester will be as well. It's been fun.

Well, here's what we ended up creating in these 2-or-so-odd months.

Unfortunately Blogger is not very good with videos.

The Solutions to your Issues Lie in the Most Obscure Places

Memory Management Revisited

So remember the issues that we were having with the Photon and its memory management? Turns out C++ is pretty hard. One simple mistyped character caused a cascade of instability.

One Character?

Yep. One character.

The model we used was essentially an operating system for the Photon, with the input device being a 5 way button thingy and the output device being the screen. The system itself was composed of "input responders," a rough classification that is used for anything that responds to user input accordingly.

This model made use of both Menus and Info screens. The menus consisted of both the location menu, which gives the location of the device using Google's Geolocation API, and several first aid menus, act as collections of responses to first aid situations. Then come the info screens, which give users the information they need to respond to various situations.

The issue we were experiencing arose with the first aid menus. Though we had passed a parameter for the number of different situations on each menu, we happened to forget that while drawing the screen. Instead, we used a constant number 5, which happened to be more than the number of situations. And because this is C++, the Photon attempts to access data that it shouldn't. Sometimes, some other data was there, which resulted in the random gibberish that sometimes popped up everywhere.

A simple fix made the device stable. Or, well, almost. There was another issue that impeded progress.

Be the Better Programmer

This issue arose from my attempt to be a good programmer. Whenever I compiled the code, the compiler always warned me about the deprecated conversion from Particle's String to a char array. So I decided to create a method that would solve this issue and convert it without the trouble.

As luck would have it, this method caused more trouble than it solved. In the conversion process, random characters were added on for some reason. Perhaps it was in the length method. or perhaps it was something else. But one way or another, these random characters were tacked on.

It was perhaps these random characters that also caused similar issues as the ones we had solved beforehand. The library we used for the Nokia 5110, our LCD, made use of a bitmap for each character in order to store how the characters should be rendered. But given how these random characters were not in the range of that array, once again, the Photon begins accessing garbage data once again. Best case scenario, it renders as blank. Common scenario, it renders as random data.

Turns out that, like most deprecated things, support still exists. So instead of going through the conversion ourselves, make the Photon do it for us. It works just fine that way.

So why the Crashing?

To be honest, I can't tell. My best guess is that either the bitmap or the array was allocated near the end of memory, so accessing out-of-bounds data resulted in attempting to access memory that doesn't exist. And the Photon responds by crashing.

Can't blame it.

Of course, this is my best guess. Perhaps someone at Particle could explain this much better than I ever could.