#pigpio

Since I haven’t written the main program yet, I’m trying out pigpio, one of tooons of gpio libraries for the Pi, just to check out the differences to wiringpi (spoiler: from the GPIO perspective, I didn’t find them super different...I’ll admit it is kind of nice not having to do all this abstraction ourselves. If you do want to level up your direct register access and embedded skillz and you’ve never done it, give it a shot! If you’re an aspiring firmware engineer, you WILL do it on the job).

The only interesting part here is that the Pi allows pullups/pulldowns on all GPIOs and interrupts on all of them as well (which is not true with all microcontrollers). That gives us a huge amount of freedom when we need to pick what needs to go to which pin.

With our little dev board, we’ve got a great starting point since all of the GPIOs are put into a spot and we just need to reference the GPIO ports we want to read from (promise, schematic is coming, just haven’t set it in stone since I need to get all these tests out of the way).

First, let’s start by downloading pigpio. Follow the instructions on this page: http://abyz.me.uk/rpi/pigpio/download.html.

If you check out the repo, under dev/buttons (https://github.com/amckeeota/UltiCon/tree/master/dev/buttons), I have two examples: buttontest.c and buttonIntTest.c. buttontest uses a polling loop and delays to check the button lines and see if anything has been pressed. Then it prints combos on the screen (try any combo and it should show which buttons you pressed). buttonIntTest registers a single function where we handle what to do with button presses and tell it we’re interested in both low to high and high to low transitions.

To build them, just type

make button

for buttontest.c or

make button_int

for buttonInt.c

For programming in C, the API docs are here: http://abyz.me.uk/rpi/pigpio/cif.html

And for python, they’re here: http://abyz.me.uk/rpi/pigpio/python.html

I’m only using C since I want the final project to be coded in C.

I only used a handful of API functions:

gpioInitialise and gpioTerminate to initialize the pigpio library

gpioSetMode to set all of the button GPIO to input

gpioSetPullUpDown to set the internal pull up resistor to the button

gpioRead for buttontest.c to read the GPIO in the polling loop

gpioSetISRFunc for buttonIntTest.c to set an interrupt in response to a button press or release

Feel free to check through my code for how to use them.

The only thing we seem to be missing is debouncing. I’m a big proponent of debouncing living in hardware just because it’s a little sloppy to deal with in software. This will guide some revision to my original board.