The WS2812 tutorial(s) use a global variable with an initializer that is called outside of the scope of any function. This is something that you can do in C++ that you really can't do in C, and I tend to think C is right where C++ is wrong.
In C the code wouldn't compile, because you can't execute code (beyond setting initializer values with builtin types) outside of a function. In C++, this is valid for constructors. The compiler puts the objects in the data segment, which is nice, as the alternative might be to call `new()` on it and get storage from the heap, which is nasty. But the compiler will generate some magic unspecified initializer function wherein it will call the constructors on the object, before it calls `main()`. And the order of those initializers is not guaranteed, so if A depends on B, you may be shit out of luck. And I especially don't trust global initializers that seem to be touching hardware. The whole thing just feels *wrong*.
With this pattern, I get the global variable, that lives in the data segment, that is initialized exactly when I want it to be initialized. The downside (some might say) is that I'm stuck with using a pointer to reference the object in memory. Someone who fears pointers could use `std::optional` and `emplace()` to do the same thing, assuming that their toolchain supports it. But I feel like that's adding complexity in layers of abstraction. It doesn't get much simpler than saying "This object lives in memory *right over there* and here is a pointer to it".
Up until now I've been using whatever pins the tutorial chose because, well, I had enough to figure out while getting my fundamental electronics lessons. But ...
<center><img alt="read the datasheet" width="320" src="readthedatasheet.jpg"/></center>
When you're following tutorials it's easy to assume "Pin X does Y thing because that's what the tutorial connected me to", and it's especially easy to think "Pin X **only** does Y thing", or "You **always** do Y thing with Pin X". This is almost never true. Each microcontroller has a datasheet from the manufacturer that tells you what all the different pins on the MCU do. The particular dev board you're using should also have a datasheet (or at least a pinout) that shows how the dev board maps all of the microcontroller pins to the devboard pins. Using these references will show you that, in fact, you can just lots of pins for lots of different functions, and that depending on how the chip is set up, a given pin may be overloaded with several different features - and that these usually can't be used together at the same time.
For example, here is the Freenove ESP32-S3 WROOM pinout from Freenove, the manufacturer of the dev board I'm using
And here is some of the pin reference documentation from Espressif on the ESP32-S3 chip itself that lives on the devboard (click each image for higher resolution - this can alos be found in chapter 2 of the datasheet from Espressif). This should tell us that the pins on our devboard aren't on the same place as the ones on the ESP32-S3 itself, they may not even be numbered the same, and the board vendor may not actually choose to expose the entire package. At least the vendor and the chip manufacturer should be using the same *names* for the pins (`GPIOxx` for example) so we can cross reference them.
The WS2812 is a series of LEDs on a strip, which can be controlled by sending a compact stream of data to the strip, and each LED takes its own data before forwarding on the rest. This allows you to control each LED individually in a theoretically endless string of LEDs with very little hardware overhead. In the particular example here, the WS2812 strip is arranged as an octagon of LEDs on a square PCB package with one `V+` line, one `GND` line, and one `S`(ignal) line.
Oh, and you control it using the **infrared remote control module** on the ESP32.
The WS2812 is controlled with a wierd single line protocol that's really efficient but very sensitive to timing. The whole thing works off of PWM signals on the wire, and there is no clock synchronization. You could do it yourself on a GPIO pin manually sending the PWM signals but it is very easy to get wrong. So the RMT module, which was originally designed to convert data to pulses and back again for sending over infrared, is abused for this purpose instead. We can just send the data and the CPU goes along its merry way.
## Calibrating joysticks
I implemented calibration logic in my code, but it was a bit lazy, and to be honest, it doesn't do what real calibration typically does. But by the time I got here, I was just ready to move on to the next project. When you press the calibration button, the calibration routine starts which continually samples over a period of time. It creates a deadzone according to the lowest and highest values seen on each axes during this time. When future joystick reads occur, anything within this deadzone are counted as being at the center of the axis. Really I did this to account for potential wobble in the joystick I hooked to the arduino, but that was unnecessary, it was remarkably stable in the center.
A real calibration routine is more advanced and allows the center to actually move. As it samples, it figures out where the center of the sample average range is, and future joystick reads return the axis movement relative to that center location. My calibration routine here can't do that. I considered changing this, but again, that was outside of the original design goal for the calibration routine.
