originally taken from https://wiki.ubuntu.com/Emulino

Emulino is an emulator for the Arduino platform by Greg Hewgill, originally found on emulino: arduino cpu emulator.

With it, you can build ("Verify") a .pde sketch in Arduino IDE which uses serial port for communication to say a .hex file, and then you can invoke the emulino executable with the .hex file as an argument, and get a local simulation of how an Arduino would behave; useful for debugging without wasting burn cycles on the Arduino's AVR chip.

Here is a brief overview of steps to get emulino built.

sudo apt-get install clang-3.6
sudo apt-get install git # to check out the source
sudo apt-get install scons # to build the source

git clone git://github.com/ghewgill/emulino.git
cd emulino/
scons install

The result is an emulino executable installed in /usr/bin.

You need to have Vagrant, VirtualBox and Ansible, but this handles all of provisioning for you. Simply do

$> vagrant up
$> vagrant ssh
$> cd /vagrant
$> scons

and you will have an emulino executible in <project-root>/build

For instance, one could use the following simple code, which simply increases a counter and writes its value on serial, as test.pde in Arduino IDE:

int counter = 0;

void setup()
{
    // initiate Arduino serial communication
    Serial.begin(115200);
}

void loop()
{
    counter = counter + 1;
    Serial.print("Counter: ");
    Serial.print(counter, DEC);
    Serial.println();
    delay(50);
}

By clicking on "Verify", the code is built - and during a "Verify" the .hex file is written to /tmp. In order to simulate the code, one can simply call emulino with the path to the hex file as argument:

$> ./emulino /tmp/build523158875647966391.tmp/test.cpp.hex
emulino: Loading hex image: /tmp/build523158875647966391.tmp/test.cpp.hex
Counter: 1
Counter: 2
Counter: 3
Counter: 4
...

Note that, in principle, emulino uses stdin and stdout of the console to simulate serial input/output. There is a command switch "-io" which should allow input/output to/from files (which have fixed names of name-of-hexfile.hex.in and name-of-hexfile.hex.out), however I cannot get it to work every time (maybe instead of files, one should use mknod and named pipes; not sure).

Note however the example below - which reads a character from serial and echoes it back to serial:

static unsigned char _c;

void setup()
{
    Serial.begin(9600);
}

void loop()
{

  // read in a byte, and send it back immediately
  // send data only when you receive data:
  if (Serial.available() > 0)
  {
      // read the incoming byte:
      _c = Serial.read();

      // say what you got:
      Serial.print(_c);
  }

  // must have delay for emulino to work
  delay(1);
}

In this example, if the delay statement is missing, then emulino will never register that a character came in from "serial"; with the delay statement, a command like session will look like:

$> stty -icanon ; ./emulino /tmp/buildXXX.tmp/test.cpp.hex
emulino: Loading hex image: /tmp/buildXXX.tmp/test.cpp.hex
tteessttiinngg  bbuuttttoonn  pprreessss^C

Note again that "stty -icanon" seems to be needed, in order to set up the terminal as a character device - so that keypresses are passed on to "stdin" per individual character basis.¯