（1）基于事件的任务调度器

一、基于事件的任务调度器

1.事件任务调度器数据结构

typedef unsigned char      bit_t;
typedef unsigned char      u1_t;
typedef   signed char      s1_t;
typedef unsigned short     u2_t;
typedef          short     s2_t;
typedef unsigned int       u4_t;
typedef          int       s4_t;
typedef unsigned long long u8_t;
typedef          long long s8_t;
typedef unsigned int       uint;
typedef const char* str_t;
typedef s4_t  ostime_t;
struct  osjob_t;  

typedef void (*osjobcb_t) (struct osjob_t*);
struct osjob_t {
    struct osjob_t* next;//链表
    ostime_t deadline;//任务执行事件
    osjobcb_t  func; //任务函数
};
TYPEDEF_xref2osjob_t;
// RUNTIME STATE 用于记录当前即时任务及计划任务；即时任务添加进即时任务链表后即时运行；计划任务则为计时时间到则运行。
static struct {
    osjob_t* scheduledjobs; /* 计划任务 */
    osjob_t* runnablejobs; /* 即时任务 */
} OS;

任务的添加和删除工作，都以回调的形式完成。

2.OS初始化及时基

  /*   系统初始化，如定时器、中断等 */
void os_init () {
/* hal_init();  */
}
 /*   获取系统时间，需要消耗MCU一个定时器来实现OS系统时基 */
ostime_t os_getTime () {
    return hal_ticks();
}

3.任务及任务链表

任务链表分两个，一个为即时任务链表，一个为定时任务链表；删除时需要从两个表中寻找并删除。

从任务链表中删除指定任务

static u1_t unlinkjob (osjob_t** pnext, osjob_t* job) {
    for( ; *pnext; pnext = &((*pnext)->next)) {
        if(*pnext == job) { // unlink
            *pnext = job->next;
            return 1;
        }
    }
    return 0;
}
// clear scheduled job
void os_clearCallback (osjob_t* job) {
    hal_disableIRQs();
    unlinkjob(&OS.scheduledjobs, job) || unlinkjob(&OS.runnablejobs, job);
    hal_enableIRQs();
}

添加任务至即时任务链表

// schedule immediately runnable job
void os_setCallback (osjob_t* job, osjobcb_t cb) {
    osjob_t** pnext;
    hal_disableIRQs();
    // remove if job was already queued
    os_clearCallback(job);
    // fill-in job
    job->func = cb;
    job->next = NULL;
    // add to end of run queue
    for(pnext=&OS.runnablejobs; *pnext; pnext=&((*pnext)->next));
    *pnext = job;
    hal_enableIRQs();
}

添加任务至计划任务链表

// schedule timed job
void os_setTimedCallback (osjob_t* job, ostime_t time, osjobcb_t cb) {
    osjob_t** pnext;
    hal_disableIRQs();
    // remove if job was already queued
    os_clearCallback(job);
    // fill-in job
    job->deadline = time;
    job->func = cb;
    job->next = NULL;
    // insert into schedule
    for(pnext=&OS.scheduledjobs; *pnext; pnext=&((*pnext)->next)) {
        if((*pnext)->deadline - time > 0) { // (cmp diff, not abs!)
            // enqueue before next element and stop
            job->next = *pnext;
            break;
        }
    }
    *pnext = job;
    hal_enableIRQs();
}

4.主任务

优先从即时任务中提取任务运行，即时任务运行完成后，才会再运行计划任务。所以，计划任务一般给对实时性无要求的任务，有时候为了保证即时任务，需要将一些任务设定为计划任务，如：点灯任务。

// execute jobs from timer and from run queue
void os_runloop () {
    while(1) {
        osjob_t* j = NULL;
        hal_disableIRQs();
        // check for runnable jobs
        if(OS.runnablejobs) {
            j = OS.runnablejobs;
            OS.runnablejobs = j->next;
        } else if(OS.scheduledjobs 
                     && hal_checkTimer(OS.scheduledjobs->deadline)) { 
                   // check for expired timed jobs
            j = OS.scheduledjobs;
            OS.scheduledjobs = j->next;
        } else { // nothing pending
            hal_sleep(); // wake by irq (timer already restarted)
        }
        hal_enableIRQs();
        if(j) { // run job callback
            j->func(j);
        }
    }
}

5.任务调度实例

static void immediatelyfunc (osjob_t* j) 
{
/*TODO*/
}
static void scheduledfunc (osjob_t* j) 
{
/*TODO*/
}
// application entry point
int main () {
    osjob_t immediatelyjob;
    osjob_t scheduledjob;
    // initialize runtime env
    os_init();
    // setup initial job 添加即时任务
    os_setCallback(&immediatelyjob, immediatelyfunc);
    // execute scheduled jobs and events
    os_setTimedCallback (&scheduledjob, 1000, scheduledfunc)
    os_runloop();// (not reached)
    return 0;
}