Programming The Teensy 3.2 Using A Makefile

The Arduino toolchain is a good starting point. So many libraries, most of them fine quality, and the editor allows you to write incorrect C++ so you can have a simpler life…

Wait, what? That’s right, the Arduino IDE does a lot of stuff to compile your program that usually does not happen in the standard C++ compilation procedure. For example, the IDE generates function prototypes for you, so that you can write your functions in whichever order you like. This alone is iffy for some. But it also automatically includes header files needed for your libraries, making the entire process rather opaque. This would have been reason enough for me to look into doing it differently, but really the elephant in the room that needed changing was the poor, often belittled Arduino IDE. The IDE simply does not do the toolchain justice.

Benefits from using Make


  • Use any editor and just run shell commands (or press buttons)
  • Compile and flash the program immediately after checking out from version control, not having to set up Arduino
  • Do syntax highlighting and completion based on local files
  • Symbol lookup (go to definition, find usage) and all the vim/IDE/ctags goodness.

The Easy Part: Using Someone Else’s Makefile

In this repo, GitHub user apmorton has prepared a working makefile. Only tiny adjustments are needed in the provided makefile, like setting desired clock frequency, setting Teensy version and enabling more compiler warning flags :)

The Hard Part: Getting Existing Code to Compile (… and run…)

I had used numerous Arduino libraries in my existing project. Here it became apparent how much the Arduino IDE actually did in the backgound - after including the libraries, there was a large wall of compiler warnings and errors. Most of them can be fixed:

  • If it is a missing (undeclared) function:
    • Looking up the header file it should be located in using google or man pages
    • Looking for that header file in ./teensy3 or ./tools using ripgrep or similar
    • Including that file, and seeing if that at least removes the error
    • When all errors are fixed, taking a hard look at all the included code, and whether it actually does the desired job
  • If the issue are duplicate function definitions:
    • Difficult one. You need to find out which of the functions to use and then comment out or guard (with a preprocessor definition) the others definition.
  • Else:
    • Tough luck, you are on your own…

The Hardest Part: Fixing Remaining Issues When The Program Compiles Fine

It is likely that after compiling with only few errors, the program still has different behaviour than when running under Arduino IDE… In my case, example code from I2Cdevlib was not setting an interrupt pin’s pinMode and thus the interrupts were ignored when not using the IDE. Presumably, the IDE does some special magic to fix this up, I don’t know. Setting the pinMode fixed this.

Good Luck!

P.S. there is an even harder part - keeping the toolchain up to date. Using platformio can fix this and get you all the benefits, but there is something to be appreciated about just running make flash

Written on November 21, 2017