• Introducing Contiki-NG Processes

Introducing Contiki-NG Processes

Contiki-NG applications can run on a process that executes in either cooperative or preemptive mode. Cooperative mode is regular execution in the micro-controller. A process with preemptive mode runs with interruptions resulting from I/O or timers. In general, we can create a process in Contiki-NG by calling PROCESS(). We can define a process as

PROCESS(inner_name,outter_name);

where

• inner_name is a variable of the process,
• outter_name is a process name that is represented as a string for users notification.

Then, we implement this process using PROCESS_THREAD. We can declare this as follows:

PROCESS_THREAD(inner_name, ev, data)
{
 PROCESS_BEGIN();
 /* Do something here. */ 
 ...
 PROCESS_END();
}

The following is a list of macros API for processes:

• PROCESS_BEGIN() - Declares the beginning of a process protothread
• PROCESS_END() - Declares the end of a process protothread
• PROCESS_EXIT() - Exits the process
• PROCESS_WAIT_EVENT() - Waits for any incoming event
• PROCESS_WAIT_EVENT_UNTIL() - Waits for an event, but with conditions
• PROCESS_YIELD() - Waits for an event; equivalent to PROCESS_WAIT_EVENT()
• PROCESS_WAIT_UNTIL() - Waits for a given condition; may not yield the micro-controller
• PROCESS_PAUSE() - Temporarily yields the micro-controller

For demo purposes, we will create a simple Contiki-NG app. Create a folder called demo-process. Then, create two files, demo-process.c and Makefile.

• demo-process.c
• Makefile

The first step is to write a program for demo-process.c. We define three processes as follows:

• demo-process.c

#include "contiki.h"
#include <stdio.h> /* For printf(); */
PROCESS(myprocess1, "process 1");
PROCESS(myprocess2, "process 2");
PROCESS(myprocess3, "process 3");
AUTOSTART_PROCESSES(&myprocess1,&myprocess2,&myprocess3);
PROCESS_THREAD(myprocess1, ev, data)
{
 PROCESS_BEGIN();
 printf("This message from process 1\n");
 PROCESS_END();
}
PROCESS_THREAD(myprocess2, ev, data)
{
 PROCESS_BEGIN();
 printf("This message from process 2\n");
 PROCESS_END();
}
PROCESS_THREAD(myprocess3, ev, data)
{
 PROCESS_BEGIN();
 printf("This message from process 3\n");
 PROCESS_END();
}

Save this program. We continue to Makefile. We declare our program and the path of the Contiki-NG root directory via CONTIKI:

• Makefile

CONTIKI_PROJECT = demo-process
all: $(CONTIKI_PROJECT)
CONTIKI = /home/user/Documents/book/contiki
include $(CONTIKI)/Makefile.include

Change the Contiki-NG path directory in CONTIKI. To compile and run the program, we can open Terminal and navigate to a program folder. We can type the following commands

make TARGET=native
./demo-process.native