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本實驗定期的打印“hello world”，并且計數打印的個數。第二線程被稱作“blink”,實現LEDs的高速閃爍（如果在Hello world線程里，可能實現不了這么快的速度）。

C++ Code

#include "contiki.h"
        #include "dev/leds.h"
        
        #include <stdio.h> /* For printf() */
        /*---------------------------------------------------------------------------*/
        /* We declare the two processes */
        PROCESS(hello_world_process, "Hello world process");
        PROCESS(blink_process, "LED blink process");
        
        /* We require the processes to be started automatically */
        AUTOSTART_PROCESSES(&hello_world_process, &blink_process);
        /*---------------------------------------------------------------------------*/
        /* Implementation of the first process */
        PROCESS_THREAD(hello_world_process, ev, data)
        {
                // variables are declared static to ensure their values are kept
                // between kernel calls.
                static struct etimer timer;
                static int count = 0;
        
                // any process mustt start with this.
                PROCESS_BEGIN();
                // set the etimer module to generate an event in one second.
                etimer_set(&timer, CLOCK_CONF_SECOND);
        
                while (1)
                {
                        // wait here for an event to happen
                        PROCESS_WAIT_EVENT();
        
                        // if the event is the timer event as expected...
                        if(ev == PROCESS_EVENT_TIMER)
                        {
                                // do the process work
                                printf("Hello, world #%i\n", count);
                                count ++;
        
                                // reset the timer so it will generate an other event
                                // the exact same time after it expired (periodicity guaranteed)
                                etimer_reset(&timer);
                        }
        
                        // and loop
                }
                // any process must end with this, even if it is never reached.
                PROCESS_END();
        }
        
        /*---------------------------------------------------------------------------*/
        /* Implementation of the second process */
        PROCESS_THREAD(blink_process, ev, data)
        {
                static struct etimer timer;
                static uint8_t leds_state = 0;
                PROCESS_BEGIN();
        
                while (1)
                {
                        // we set the timer from here every time
                        etimer_set(&timer, CLOCK_CONF_SECOND / 4);
                        // and wait until the vent we receive is the one we're waiting for
                        PROCESS_WAIT_EVENT_UNTIL(ev == PROCESS_EVENT_TIMER);
        
                        // update the LEDs
                        leds_off(0xFF);
                        leds_on(leds_state);
                        leds_state += 1;
                }
                PROCESS_END();
        }
        /*---------------------------------------------------------------------------*/

1、線程啟動流程

a) 聲明線程PROCESS(name, strname)，name線程名字，strname對線程名字的描述。

b) AUTOSTART_PROCESSES(&hello_world_process, &blink_process)開啟線程。

c) PROCESS_THREAD(hello_world_process, ev, data)線程宏定義。

第一個參數lc是英文全稱是local continuation（本地延續？，這個不好翻譯），它可以說就是protothread的控制參數，因為protothread的精華在C的switch控制語句，這個lc就是switch里面的參數；

第二個參數就是timer給這個進程傳遞的事件了，其實就是一個unsigned char類型的參數，具體的參數值在process .h中定義；

第三個參數也是給進程傳遞的一個參數（舉個例子，假如要退出一個進程的話，那么必須把這個進程所對應的timer也要從timer隊列timerlist清除掉，那么進程在死掉之前就要給etimer_process傳遞這個參數，參數的值就是進程本身，這樣才能是etimer_process在timer隊列里找到相應的etimer進而清除）。