Arduino, Day 1

A friend of mine sent me a RedBoard and asked me to collaborate with him on a development idea. So I'm playing with an Arduino-compatible device for the first time. I've been aware of them, but just never got one, in part because after writing embedded code all day, what I've wanted to do with my time off is not necessarily write more embedded code.

I downloaded the Arduino IDE and checked that out a bit. There are some things about the way it's presented that drive me a little batty. The language is C++, but Arduino calls it the "Arduino Programming Language" -- it even has its own language reference page. Down at the bottom the fine print says "The Arduino language is based on C/C++."

That repels me. First, it seems to give the Arduino team credit for creating something that they really haven't. They deserve plenty of credit -- not least for building a very useful library -- but not for inventing a programming language. Second, it fails to give credit (and blame) for the language to the large number of people who actually designed and implemented C, C++, and the GCC cross-compiler running behind the scenes, with its reduced standard libraries and all. And third, it obfuscates what programmers are learning -- especially the distinction between a language and a library. That might keep things simpler for beginners but this is supposed to be a teaching tool, isn't it? I don't think it's a good idea to obfuscate the difference between the core language (for example, bitwise and arithmetic operators), macros (like min), and functions in the standard Arduino library. For one thing, errors in using each of these will result in profoundly different kinds of diagnostic messages or other failure modes. It also obfuscates something important -- which C++ is this? Because C++ has many variations now. Can I use enum classes or other C++11 features? I don't know, and because of the facade that Arduino is a distinct language, it is harder to find out. They even have the gall to list true and false as constants. If there's one thing C and C++ programmers know, and beginners need to learn quickly, it's that logical truth in C and C++ is messy. I would hate to have to explain to a beginner why testing a masked bit that is not equal to one against true does not give the expected result.

Anyway, all that aside, this is C++ where the IDE does a few hidden things for you when you compile your code. It inserts a standard header, Arduino.h. It links you to a standard main(). I guess that's all helpful. But finally, it generates prototypes for your functions. That implies a parsing stage, via a separate tool that is not a C++ compiler.

On my Mac Pro running Mountain Lion, the board was not recognized as a serial device at all, so I had to give up using my Mac, at least until I can resolve that. I switched over to Ubuntu 12.04 on a ThinkPad laptop. The IDE works flawlessly. I tried to follow some directions to see where the code was actually built by engaging a verbose mode for compilation and uploading, but I couldn't get that working. So I ditched the IDE.

This was fairly easy, with the caveat that there are a bunch of outdated tools out there. I went down some dead ends and rabbit holes, but the procedure is really not hard. I used sudo apt-get install to install arduino-core and arduino-mk.

There is now a common Arduino.mk makefile in my /usr/share/arduino directory and I can make project folders with makefiles that refer to it. To make this work I had to add a new export to my .bashrc file, export ARDUINO_DIR=/usr/share/arduino (your mileage may vary depending on how your Linux version works, but that's where I define additional environment variables).

The Makefile in my project directory has the following in it:

BOARD_TAG    = uno
ARDUINO_PORT = /dev/serial/by-id/usb-*
include /usr/share/arduino/Arduino.mk

And nothing else! Everything else is inherited from the common Arduino.mk. I can throw .cpp and .h files in there and make builds them and make upload uploads them.

If you have trouble with the upload, you might take a look at your devices. A little experimentation (listing the contents of /dev before and after unpluging the board) reveals that the RedBoard is showing up on my system as a device under /dev/serial -- in my case, /dev/serial/by-id/usb-FTDI_FT232R_USB_UART_A601EGHT-if00-port0 and /dev/serial/by-path/pci-0000:00:1d.0-usb-0:2:1.0-port0 (your values will no doubt vary). That's why my Makefile reads ARDUINO_PORT = /dev/serial/by-id/usb-* -- so it will catch anything that shows up in there with the usb- prefix. If your device is showing up elsewhere, or you have more than one device, you might need to tweak this to properly identify your board.

When you look at the basic blink demo program in the Arduino IDE, you see this, the contents of an .ino file (I have removed some comments):

int led = 13;

void setup() {                
    // initialize the digital pin as an output.
    pinMode(led, OUTPUT);     
}

// the loop routine runs over and over again forever:
void loop() {
    digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(1000);               // wait for a second
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    delay(1000);               // wait for a second
}

The Makefile knows how to build an .ino file and inserts the necessary header, implementation of main, and generates any necessary prototypes. But if you want to build this code with make as a .cpp file, it needs to look like this:

#include <Arduino.h>

int led = 13;

void setup() {
    // initialize the digital pin as an output.
    pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
    digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(1000);               // wait for a second
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    delay(1000);               // wait for a second
}

int main(void)
{
    init();

#if defined(USBCON)
    USBDevice.attach();
#endif

    setup();

    for (;;) {
        loop();
        if (serialEventRun) serialEventRun();
    }

return 0;

}

And there it is -- C++, make, and no IDE. Relaxen and watchen Das blinkenlights!