无线传感网络--开源框架Contiki3.0基本原理

引言：
在无线传感器的领域之中，Contiki是一个很好的开源框架。在IAR工作环境当中，利用Contiki框架对无线传感器模块进行烧写。接下来，就让笔者粗略分析一下Contiki框架的内容以及工作原理。

• 1）以下是在IAR工作环境中的一段简易的利用Contiki编写的部分源码。
  大致过程是：将编写的程序以单个进程为载体调用Contiki框架中的库文件，依次调用库文件执行相应的操作。

• 2）接下来分析一下Contiki进程头文件process.h以及源文件process.c：
  头文件process.h当中是对源文件process.h的一些宏定义，故在此不加以叙述，重点分析一下进程的源文件process.c
  源码如下（版权问题，仅供参考）：
  
  内核进程代码部分：

//版权所有，仅供读者学习参考
/*
 * Copyright (c) 2005, Swedish Institute of Computer Science
 * All rights reserved.
 * /

#include 
#include "sys/process.h"
#include "sys/arg.h"
/*
 * Pointer to the currently running process structure.
 */
struct process *process_list = NULL;
struct process *process_current = NULL;
static process_event_t lastevent;
/*
 * Structure used for keeping the queue of active events.
 */
struct event_data {
  process_event_t ev;
  process_data_t data;
  struct process *p;
};
static process_num_events_t nevents, fevent;
static struct event_data events[PROCESS_CONF_NUMEVENTS];

#if PROCESS_CONF_STATS
process_num_events_t process_maxevents;
#endif

static volatile unsigned char poll_requested;

#define PROCESS_STATE_NONE        0
#define PROCESS_STATE_RUNNING     1
#define PROCESS_STATE_CALLED      2

static void call_process(struct process *p, process_event_t ev, process_data_t data);

#define DEBUG 0
#if DEBUG
#include 
#define PRINTF(...) printf(__VA_ARGS__)
#else
#define PRINTF(...)
#endif

process_event_t
process_alloc_event(void)
{
  return lastevent++;
}

//1.进程start()
void
process_start(struct process *p, process_data_t data)
{
  struct process *q;

  /* First make sure that we don't try to start a process that is
     already running. */
  for(q = process_list; q != p && q != NULL; q = q->next);

  /* If we found the process on the process list, we bail out. */
  if(q == p) {
    return;
  }
  /* Put on the procs list.*/
  p->next = process_list;
  process_list = p;
  p->state = PROCESS_STATE_RUNNING;
  PT_INIT(&p->pt);

  PRINTF("process: starting '%s'\n", PROCESS_NAME_STRING(p));

  /* Post a synchronous initialization event to the process. */
  process_post_synch(p, PROCESS_EVENT_INIT, data);
}

//2.进程exit()
static void
exit_process(struct process *p, struct process *fromprocess)
{
  register struct process *q;
  struct process *old_current = process_current;

  PRINTF("process: exit_process '%s'\n", PROCESS_NAME_STRING(p));

  /* Make sure the process is in the process list before we try to
     exit it. */
  for(q = process_list; q != p && q != NULL; q = q->next);
  if(q == NULL) {
    return;
  }

  if(process_is_running(p)) {
    /* Process was running */
    p->state = PROCESS_STATE_NONE;

    /*
     * Post a synchronous event to all processes to inform them that
     * this process is about to exit. This will allow services to
     * deallocate state associated with this process.
     */
    for(q = process_list; q != NULL; q = q->next) {
      if(p != q) {
    call_process(q, PROCESS_EVENT_EXITED, (process_data_t)p);
      }
    }

    if(p->thread != NULL && p != fromprocess) {
      /* Post the exit event to the process that is about to exit. */
      process_current = p;
      p->thread(&p->pt, PROCESS_EVENT_EXIT, NULL);
    }
  }

  if(p == process_list) {
    process_list = process_list->next;
  } else {
    for(q = process_list; q != NULL; q = q->next) {
      if(q->next == p) {
    q->next = p->next;
    break;
      }
    }
  }

  process_current = old_current;
}

//3.进程call()
static void
call_process(struct process *p, process_event_t ev, process_data_t data)
{
  int ret;

#if DEBUG
  if(p->state == PROCESS_STATE_CALLED) {
    printf("process: process '%s' called again with event %d\n", PROCESS_NAME_STRING(p), ev);
  }
#endif /* DEBUG */

  if((p->state & PROCESS_STATE_RUNNING) &&
     p->thread != NULL) {
    PRINTF("process: calling process '%s' with event %d\n", PROCESS_NAME_STRING(p), ev);
    process_current = p;
    p->state = PROCESS_STATE_CALLED;
    ret = p->thread(&p->pt, ev, data);
    if(ret == PT_EXITED ||
       ret == PT_ENDED ||
       ev == PROCESS_EVENT_EXIT) {
      exit_process(p, p);
    } else {
      p->state = PROCESS_STATE_RUNNING;
    }
  }
}

//4.进程exit()
void
process_exit(struct process *p)
{
  exit_process(p, PROCESS_CURRENT());
}

//5.进程init()
void
process_init(void)
{
  lastevent = PROCESS_EVENT_MAX;

  nevents = fevent = 0;
#if PROCESS_CONF_STATS
  process_maxevents = 0;
#endif /* PROCESS_CONF_STATS */

  process_current = process_list = NULL;
}

//6.进程call() poll's handler
static void
do_poll(void)
{
  struct process *p;

  poll_requested = 0;
  /* Call the processes that needs to be polled. */
  for(p = process_list; p != NULL; p = p->next) {
    if(p->needspoll) {
      p->state = PROCESS_STATE_RUNNING;
      p->needspoll = 0;
      call_process(p, PROCESS_EVENT_POLL, NULL);
    }
  }
}
//7.事件do_event()
static void
do_event(void)
{
  static process_event_t ev;
  static process_data_t data;
  static struct process *receiver;
  static struct process *p;

  /*
   * If there are any events in the queue, take the first one and walk
   * through the list of processes to see if the event should be
   * delivered to any of them. If so, we call the event handler
   * function for the process. We only process one event at a time and
   * call the poll handlers inbetween.
   */

  if(nevents > 0) {

    /* There are events that we should deliver. */
    ev = events[fevent].ev;

    data = events[fevent].data;
    receiver = events[fevent].p;

    /* Since we have seen the new event, we move pointer upwards
       and decrease the number of events. */
    fevent = (fevent + 1) % PROCESS_CONF_NUMEVENTS;
    --nevents;

    /* If this is a broadcast event, we deliver it to all events, in
       order of their priority. */
    if(receiver == PROCESS_BROADCAST) {
      for(p = process_list; p != NULL; p = p->next) {

    /* If we have been requested to poll a process, we do this in
       between processing the broadcast event. */
    if(poll_requested) {
      do_poll();
    }
    call_process(p, ev, data);
      }
    } else {
      /* This is not a broadcast event, so we deliver it to the
     specified process. */
      /* If the event was an INIT event, we should also update the
     state of the process. */
      if(ev == PROCESS_EVENT_INIT) {
    receiver->state = PROCESS_STATE_RUNNING;
      }

      /* Make sure that the process actually is running. */
      call_process(receiver, ev, data);
    }
  }
}

//8.进程run()
int
process_run(void)
{
  /* Process poll events. */
  if(poll_requested) {
    do_poll();
  }

  /* Process one event from the queue */
  do_event();

  return nevents + poll_requested;
}
//9.事件process_nevents()
int
process_nevents(void)
{
  return nevents + poll_requested;
}

//10.进程发送process_post()
int
process_post(struct process *p, process_event_t ev, process_data_t data)
{
  static process_num_events_t snum;

  if(PROCESS_CURRENT() == NULL) {
    PRINTF("process_post: NULL process posts event %d to process '%s', nevents %d\n",
       ev,PROCESS_NAME_STRING(p), nevents);
  } else {
    PRINTF("process_post: Process '%s' posts event %d to process '%s', nevents %d\n",
       PROCESS_NAME_STRING(PROCESS_CURRENT()), ev,
       p == PROCESS_BROADCAST? "": PROCESS_NAME_STRING(p), nevents);
  }

  if(nevents == PROCESS_CONF_NUMEVENTS) {
#if DEBUG
    if(p == PROCESS_BROADCAST) {
      printf("soft panic: event queue is full when broadcast event %d was posted from %s\n", ev, PROCESS_NAME_STRING(process_current));
    } else {
      printf("soft panic: event queue is full when event %d was posted to %s from %s\n", ev, PROCESS_NAME_STRING(p), PROCESS_NAME_STRING(process_current));
    }
#endif /* DEBUG */
    return PROCESS_ERR_FULL;
  }

  snum = (process_num_events_t)(fevent + nevents) % PROCESS_CONF_NUMEVENTS;
  events[snum].ev = ev;
  events[snum].data = data;
  events[snum].p = p;
  ++nevents;

#if PROCESS_CONF_STATS
  if(nevents > process_maxevents) {
    process_maxevents = nevents;
  }
#endif /* PROCESS_CONF_STATS */

  return PROCESS_ERR_OK;
}

//11.进程发送特征值
void
process_post_synch(struct process *p, process_event_t ev, process_data_t data)
{
  struct process *caller = process_current;

  call_process(p, ev, data);
  process_current = caller;
}

//12.进程poll()
void
process_poll(struct process *p)
{
  if(p != NULL) {
    if(p->state == PROCESS_STATE_RUNNING ||
       p->state == PROCESS_STATE_CALLED) {
      p->needspoll = 1;
      poll_requested = 1;
    }
  }
}

//13.进程运行判断
int
process_is_running(struct process *p)
{
  return p->state != PROCESS_STATE_NONE;
}

鉴于笔者能力有限，不能一一描述内核其他文件的内容，故将进程部分贴出来。如果有兴趣者可以自行通过IAR IDE进行debug测试。