Servo - September 2010

We’re not out of the woods just yet. The nxtcom program cannot be executed; we have to change its file attributes. To make nxtcom executable, type chmod +x nxtcom. Now, we can assemble NBC files with the nbc program and download them to the NXT with nxtcom.

As I said before, I didn’t know any of this when I started so I asked my friend Joe (thanks Joe!) to help me out. He sent me a simple Makefile that showed the steps to use to compile and download NXC code to the NXT brick. In Listing 1, you will see the Makefile which is a UNIX scripting language that “simplifies” using compilers, linkers, programmers, and other complicated command line things so you can type short and simple commands to get things done. (More on this later.) One key thing that you need to remember about a Makefile is that it needs to have the “M” at the beginning of the name capitalized. Why? Don’t know, it’s just an ancient UNIX custom.

It would take a whole column to explain this Makefile, so I won’t do that. I’ll just point out that it sets up where the compiler and download program are (nbc and nxtcom), and the compiler options to use to compile your code and download it over the USB port. Using the Bluetooth port can be set too. If anyone is interested, I’ll do that question separately since it’s more fun setting up the Bluetooth connections.

Listing 1 shows Joe’s Makefile after I modified it. We’ll come back to it later to explain what is going on and why I made the changes that I did. Joe initially put all of his source files in the same directory as the nbc assembler. I like to put applications in the Applications folder and programming projects in the Documents folder, so before we go any further, let’s create a NXC projects folder here: Documents/NXC/projects/ first.

You can create this folder path in Finder or you can do it in your terminal window if you know the UNIX commands to do so (mkdir). (I did mine in Finder.)

Next, we’ll create a simple program to read a SONAR sensor and display the results on the NXT screen. Listing 2 shows this source. This was my first program written in NXC. These files are in the first folder we created

Figure 2. NXC application folder layout.

in the last paragraph.

Let’s see ... we’ve installed the NXC compiler, have a Makefile, and a source file — we’re ready to go. I tried to make the program and it failed. The compiler could not find the NXCDefs.h file. I searched the SourceForge site and Googled everything that I could to find out where to get this file. I found no mention of it. When you take the “road less traveled” (Mac) and are using open source tools, you must be ready to dust off your brain cells to figure out how to get things to work. Many open source tools are built for the fun of it and out of the kindness of some hard working person. Usually, there are holes in the documentation that we must fill in while actually figuring out how things work. This was one such time.