Contiki內(nèi)核結(jié)構(gòu)

嵌入式系統(tǒng)可以看作是一個(gè)運(yùn)行著死循環(huán)主函數(shù)系統(tǒng)，Contiki內(nèi)核是基于事件驅(qū)動(dòng)的椎工，系統(tǒng)運(yùn)行可以視為不斷處理事件的過程。Contiki整個(gè)運(yùn)行是通過事件觸發(fā)完成，一個(gè)事件綁定相應(yīng)的進(jìn)程馋劈。當(dāng)事件被觸發(fā)，系統(tǒng)把執(zhí)行權(quán)交給事件所綁定的進(jìn)程晾嘶，contiki系統(tǒng)運(yùn)行原理示意圖如下所示：

contiki系統(tǒng)的process

contiki系統(tǒng)中process的結(jié)構(gòu)體如下所示：

struct process {

struct process *next;

#if PROCESS_CONF_NO_PROCESS_NAMES? /* More CODE space savings by turning off process names */

#define PROCESS_NAME_STRING(process) ""

#else

const char *name;

#define PROCESS_NAME_STRING(process) (process)->name

#endif

PT_THREAD((* thread)(struct pt *, process_event_t, process_data_t));

struct pt pt; ?

unsigned char state, needspoll; ?

};

next：contiki事件以單鏈表形式存儲(chǔ)妓雾，此處指向當(dāng)前事件的下一個(gè)事件地址，contiki定義了一個(gè)process_list的全局變量來標(biāo)記事件的表頭垒迂；

PROCESS_CONF_NO_PROCESS_NAMES：進(jìn)程名稱械姻，為0時(shí)進(jìn)程名稱為空字符串；

pt：記錄當(dāng)前中斷狀態(tài)机断，其實(shí)是一個(gè)void*的指針楷拳，用來保存被中斷的行數(shù)；

state：標(biāo)記進(jìn)程的狀態(tài)吏奸，共有三種狀態(tài)欢揖，分別為：PROCESS_STATE_NONE， PROCESS_STATE_RUNNING奋蔚， PROCESS_STATE_CALLED她混；

needspoll：進(jìn)程優(yōu)先級(jí)，取值為0 或者1泊碑，為1表示優(yōu)先級(jí)更高坤按，需要將該進(jìn)程插入到其他普通進(jìn)程前；

PT_THREAD：進(jìn)程處理函數(shù)馒过，此處為一個(gè)函數(shù)的指針臭脓；struct pt *用來標(biāo)記進(jìn)程狀態(tài)；process_event_t為進(jìn)程中事件的名稱沉桌，原型為unsigned char谢鹊；process_data_t為進(jìn)程傳遞的參數(shù)，原型為void *類型留凭；

進(jìn)程調(diào)度

進(jìn)程創(chuàng)建

創(chuàng)建進(jìn)程實(shí)際上是定義一個(gè)進(jìn)程控制塊和進(jìn)程執(zhí)行體的函數(shù)佃扼；PROCESS宏定義即可用來定義一個(gè)進(jìn)程控制塊和聲明一個(gè)進(jìn)程執(zhí)行體函數(shù)，name為進(jìn)程控制塊蔼夜，PROCESS_THREAD為進(jìn)程執(zhí)行體函數(shù)兼耀。

#define PROCESS(name, strname) \

PROCESS_THREAD(name, ev, data); \

struct process name = { NULL, strname, \

process_thread_##name }

需要注意的是，PROCESS宏定義只是對(duì)進(jìn)程的執(zhí)行函數(shù)做了聲明，但是并沒有定義瘤运，所以還需要對(duì)PROCESS_THREAD函數(shù)進(jìn)行定義窍霞；

PROCESS_THREAD(hello_world_process, ev, data)

{

PROCESS_BEGIN();

printf("Hello World!\n");

PROCESS_END();

}

進(jìn)程創(chuàng)建完成之后，通過process_start函數(shù)將新創(chuàng)建的進(jìn)程加入到進(jìn)程執(zhí)行鏈表里拯坟，process_start的核心代碼如下所示但金；

/* Put on the procs list.*/

p->next = process_list;//將進(jìn)程添加到進(jìn)程鏈表的頭部

process_list = p;//更新進(jìn)程鏈表頭部

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);

process_post_synch為進(jìn)程同步函數(shù)，內(nèi)部直接調(diào)用call_process函數(shù)郁季，此處將進(jìn)程狀態(tài)置為PROCESS_STATE_RUNNING冷溃，所以第一次將新創(chuàng)建的進(jìn)程加入到進(jìn)程鏈表的時(shí)候，會(huì)執(zhí)行一遍進(jìn)程的thread函數(shù)梦裂，然后通過exit_process函數(shù)將state置為PROCESS_STATE_NONE似枕，exit_process函數(shù)核心代碼如下所示；

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) { //通知其他進(jìn)程當(dāng)前進(jìn)程已經(jīng)退出年柠，回收相關(guān)系統(tǒng)資源

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) { ?//如果當(dāng)前進(jìn)程p為process_list的頭節(jié)點(diǎn)凿歼，則將process_list指向它的next；

process_list = process_list->next;

} else { ?//如果當(dāng)前進(jìn)程p不為process_list的頭節(jié)點(diǎn)冗恨，則將p的上一個(gè)節(jié)點(diǎn)的next指向p的next答憔，即將p節(jié)點(diǎn)從鏈表中去除掉；

for(q = process_list; q != NULL; q = q->next) {

if(q->next == p) {

q->next = p->next;

break;

...

和process_post_synch對(duì)應(yīng)的為process_post派近，該函數(shù)為進(jìn)程異步函數(shù)攀唯，調(diào)用process_post函數(shù)處理事件時(shí)，事件并未立即處理渴丸，而是被加入到事件等待處理隊(duì)列nevents里侯嘀，等待下一次process_run的時(shí)候，通過do_event函數(shù)來執(zhí)行谱轨。

進(jìn)程加入到進(jìn)程執(zhí)行鏈表之后戒幔，通過process_run函數(shù)來進(jìn)行進(jìn)程的輪詢調(diào)用，process_run核心代碼如下所示土童；即先執(zhí)行優(yōu)先級(jí)比較高的進(jìn)程诗茎，再執(zhí)行普通進(jìn)程。

if(poll_requested) {

do_poll();

}

/* Process one event from the queue */

do_event();

進(jìn)程優(yōu)先級(jí)

contiki只有兩種類型的進(jìn)程調(diào)度優(yōu)先級(jí)献汗，用process中的needspoll標(biāo)記敢订，默認(rèn)為0，即普通優(yōu)先級(jí)罢吃；可以在創(chuàng)建該進(jìn)程時(shí)設(shè)置其優(yōu)先級(jí)楚午；在進(jìn)程運(yùn)行時(shí)會(huì)優(yōu)先檢查高優(yōu)先級(jí)的進(jìn)程；process_run函數(shù)原型如下：

int

process_run(void)

{

/* Process poll events. */

if(poll_requested) {

do_poll();

}

/* Process one event from the queue */

do_event();

return nevents + poll_requested;

}

poll_requested：全局變量尿招，是否有高優(yōu)先級(jí)事件的標(biāo)志位矾柜，初始化為0阱驾，在函數(shù)process_poll里進(jìn)行置位；

do_poll：函數(shù)原型如下所示怪蔑，遍歷整個(gè)進(jìn)程鏈表里覆，查看進(jìn)程優(yōu)先級(jí)，如果進(jìn)程的needspoll標(biāo)志位為1缆瓣，則優(yōu)先執(zhí)行該進(jìn)程喧枷，將其狀態(tài)標(biāo)記為PROCESS_STATE_RUNNING，然后調(diào)用call_process執(zhí)行該進(jìn)程捆愁；

/* 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);

}

call_process函數(shù)核心代碼如下：

if((p->state & PROCESS_STATE_RUNNING) &&

p->thread != NULL) {//如果當(dāng)前進(jìn)程的狀態(tài)是PROCESS_STATE_RUNNING模式割去，并且thread函數(shù)不為NULL

PRINTF("process: calling process '%s' with event %d\n", PROCESS_NAME_STRING(p), ev);

process_current = p;

p->state = PROCESS_STATE_CALLED;//將進(jìn)程的狀態(tài)置為PROCESS_STATE_CALLED

ret = p->thread(&p->pt, ev, data);//運(yùn)行進(jìn)程函數(shù)thread窟却，返回值為ret

if(ret == PT_EXITED ||

ret == PT_ENDED ||

ev == PROCESS_EVENT_EXIT) {

exit_process(p, p);//如果該進(jìn)程被正常執(zhí)行昼丑，則退出該進(jìn)程

} else {

p->state = PROCESS_STATE_RUNNING;

}

以上即為contiki系統(tǒng)process管理的整個(gè)過程，主要分為進(jìn)程創(chuàng)建和進(jìn)程管理兩大部分內(nèi)容夸赫，進(jìn)程創(chuàng)建其實(shí)就是對(duì)進(jìn)程控制塊和進(jìn)程執(zhí)行函數(shù)進(jìn)行注冊(cè)和聲明菩帝；進(jìn)程管理其實(shí)就是對(duì)進(jìn)程各個(gè)狀態(tài)的維護(hù)和處理。

contiki系統(tǒng)的事件

事件也是contiki系統(tǒng)的重要組成部分茬腿，在contiki系統(tǒng)中呼奢，當(dāng)有事件傳遞給進(jìn)程時(shí)，就會(huì)新建一個(gè)事件加入事件隊(duì)列切平，并綁定該進(jìn)程握础；一個(gè)進(jìn)程可以對(duì)應(yīng)多個(gè)事件，一個(gè)事件也可以通知給所有的進(jìn)程悴品；事件的數(shù)據(jù)結(jié)構(gòu)如下所示禀综；

struct event_data {

process_event_t ev; ? //unsigned char

process_data_t data; ?//void *

struct process *p;

};

ev：標(biāo)識(shí)所產(chǎn)生事件ID，0x80-0x8F為系統(tǒng)事件ID苔严，其余的為用戶可自定義的事件ID定枷；

data：保存事件產(chǎn)生時(shí)獲得的相關(guān)信息，即事件產(chǎn)生后可以給進(jìn)程傳遞的數(shù)據(jù)届氢；

p：指向監(jiān)聽該事件的進(jìn)程欠窒；

static struct event_data events[PROCESS_CONF_NUMEVENTS];

通過PROCESS_CONF_NUMEVENTS宏定義來確定事件隊(duì)列的大小退子；將需要執(zhí)行的事件加入到events隊(duì)列中岖妄，在系統(tǒng)調(diào)用process_run的時(shí)候，通過調(diào)用do_event函數(shù)來執(zhí)行events隊(duì)列中的事件寂祥；do_event核心代碼如下所示荐虐；

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);

}

}

如果事件隊(duì)列里有需要執(zhí)行的事件，則通過call_process函數(shù)將該事件的相關(guān)參數(shù)傳遞給相應(yīng)的process進(jìn)行執(zhí)行壤靶。