Step 49Software: Introduction

The software is written in C and compiled with the open source compiler avr-gcc. This is the main reason we use Atmel AVR micro controllers. The PIC series from Microchip is also a nice choice, but most of the C compilers cost money, and the free versions have limitations on code size.

The AVR route is much more hassle free. Just apt-get install the avr-gcc compiler, and you're in business.

The software on the AVR consists of two main components, the cube interrupt routine and effect code for making fancy animations.

When we finally finished soldering, we thought this would be the easy part. But it turns out that making animations in monochrome at low resolutions is harder than it sounds.

If the display had a higher resolution and more colors, we could have used sin() and cos() functions and all that to make fancy eye candy. With two colors (on and off) and low resolution, we have to use a lot of if() and for() to make anything meaningful.

In the next few steps, we will take you on a tour of some of the animations we made and how they work. Our goal is to give you an understanding of how you can make animations, and inspire you to create your own! If you do, please post a video in the comments!

Step 50Software: How it works

As mentioned in the previous step, the software consists of two pars. The interrupt routine and the effect code.

Communication between these two happens via a voxel array. This array has a bit for every LED in the LED cube. We will refer to this as the cube array or cube buffer from now on.

The cube array is made of 8x8 bytes. Since each byte is 8 bits, this gives us a buffer that is 8 voxels wide, 8 woxels high and 8 voxels deep (1 byte deep).

volatile unsigned char cube[8][8];

The interrupt routine reads from the cube array at given intervals and displays the information on the LED cube.

The effect functions writes the desired LED statuses to this array.

We did not use any synchronization or double buffering, since there is only one producer (either the effects currently running, or input from RS232) and one consumer (the interrupt-code that updates the cube). This means that some voxels could be from the next or previous "frame", but this is not a problem, since the frame rate is so high.

When working with micro controllers, code size is critical. To save code size and programming work, and to make the code easier to read, we have tried to write re-usable code as often as possible.

The LED cube code has a base of low level drawing functions that are used by the higher level effect functions. The draw functions can be found in draw.c. Draw functions include everything from setting or clearing a single voxel to drawing lines and wireframe boxes.