Files For This Tutorial

Tutorial

This tutorial will guide you through the basic ussage of Nifty in combination with Cooja. We assume, that we have a C library on our nodes that we want to interface with. The header file answer.h looks as following:

extern int answer(int n);

The implementation in answer.c looks like this:

int
answer(int n) {
  return 42 + n;
}

Creating an Interface

We start creating an interface using Nifty:

1> nifty:compile("answer.h", mote_answer, []).
ok

This will create the files mote_answer.erl and contiki_app.c. mote_answer.erl contains the supprt library that is required to operate the interface. contiki_app.c contains a Contiki application that operates the interface in the Contiki firmware.

Compiling the firmware

When we compile the firmware, it is important to include the created contiki_app.c and the library sources answer.c. A Makefile coulde look like this:

all: contiki_app
PROJECT_SOURCEFILES+=answer.c
include $(CONTIKI)/Makefile.include

Creating a Simulation

We need to create a simulation containing nodes with the firmware using the interface. It is also neccesary to use the Socket Controll plugin that allows us to control Cooja with Nifty.

Starting Everything

Now we can start the simulation and call the functions. We need to subscribe to the motes serial line and wait for it to be initialized. Nifty provides the function wait_for_msg/4 which waits for a messages on a given mote. The third argument is a timeout and the function will return false if it runs out. The message can be any regular expression. If it is possible to match the message against the mote output, the function returns true:

2> Handler = nifty_cooja:start("$CONTIKI/tools/cooja", "$PWD/simulation.csc").
{handler, <7212.2.0>}
3> Motes = nifty_cooja:motes(Handler).
[1]
4> nifty_cooja:mote_listen(Handler, 1).
ok
5> nifty_cooja:wait_for_msg(Handler, 1, 1000, "Starting 'Process mote_answer'\n").
true

Now we can call the interface functions. In addition to the function arguments, we need to give the simulation handler and the mote ID as the firt two arguments:

6> c(answer).
{ok, answer}
7> answer:answer(Handler, 1, 10).
52

Debug Output

Messages starting with DEBUG are ignored by nifty-contiki. If you need to print some debug information, you can prefix the output with DEBUG:

int value=42;
printf("DEBUG: important value %d\n", value);

Events

Sometimes you need to return a value from an asynchronous event (in a callback function or similar). Nifty provides an event system to do this. Messages prefixed with EVENT: are interpreted as events and ignored during normal operations (similar to debug output):

printf("EVENT:connected\n");

Events can be read using the next_event/2 function:

1> nifty_cooja:next_event(Handler, 2).
"connected"

next_event/2 will return fail if no event has occured yet.