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REX系统2

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标签:mic   val   disable   resume   void   中断处理程序   led   等待队列   super   

REX(Real Time Executive)是一个面向嵌入式应用的,简单高效的,抢先式,多任务实时操作系统,支持基于优先级的任务调度算法(支持优先级反转)。它提供了任务控制,任务同步,互斥,定时器和终端控制等API。

  REX所有的函数都在任务上下文环境里执行。

  REX只需要少于5k的ROM控件,需要的RAM空间取决于运行的任务数目加上几k字节的状态数据和堆栈空间。

  REX处理了IRQ中断。

 

1. 数据定义与宏定义

  1.1 数据结构

  rex.h中定义了REX中的各种数据结构。

  1.1.1 TCB(任务控制块)

  * 用于描述一个REX任务

  * 不能被外部直接访问

  * 由于内核按照排列书序对其进行访问,结构中数据的排列顺序不能更改。

typedef struct rex_tcb_struct{

  void  *sp;  //堆栈指针

  void  *stack_limit; //堆栈限值

  unsigned long  slices;  //任务的时间片

  rex_sigs_type  sigs;  //当前持有的信号量

  rex_sigs_type  wait;  //等待获取的信号量

  rex_priority_type  pri;  //任务优先级

  #if defined FEATURE_REX_PROFILE

    unsigned long  time_samples;  //profiling information

    unsigned long  max_intlock_time;  //profiling info

  #endif

  #if defined TIMETEST

    word  leds;  //TIMETEST val

  #endif

  #if defined FEATURE_SOFTWARE_PROFILE

    //32 bits counter, ~30 usec/tick, ~35 hours

    dword  numticks;

  #endif

  #ifdef FEATURE_REX_APC

    long  num_apcs;  //APC调用数目

  #endif

  //以上数据域的偏移量已经在rexarm.h中定义。注意保持两者一致

  rex_tcb_link_type  cs_link;  //当等待临街区域时,为非空

  rex_crit_sect_type  *cs_stack[REX_CRIT_SECT_MAX];  //持有和等待临界区的TCB堆栈

  rex_crit_sect_type  **cs_sp;  //临界区堆栈指针

  boolean  suspended;  //任务是否挂起

  char  task_name[REX_TASK_NAME_LEN + 1];

  #if defined FEATURE_REX_EXTENDED_COUNTEXT

    void  *ext;

  #endif

 

  unsigned long  thread_id;

  unsigned long  stack_size;

  //检查task堆栈的使用情况,该特性没有打开

  #ifdef FEATURE_SI_STACK_WM

    unsigned long  stack_wm;

  #endif

  //用于BSD socket数据服务

  #if defined FEATURE_DS_SOCKETS_BSD

    void  *bsdcb_ptr;

  #endif

  int  err_num;  //error code

  //用于在task被阻塞时,通知dog停止监视

  int  dog_report_val;  //dog report id

  int  autodog_enabled;  //dog report enabled ?

  #if defined FEATURE_REX_CREATE_TASK || defined FEATURE_ZREX

    boolean  is_dynamic;

  #endif

  #ifdef FEATURE_REX_IPC

    rex_ipc_info_type  ipc_info;

  #endif

}rex_tcb_type;

 

1.1.2 定时器(timer)数据结构

  *描述REX使用的定时器

  *不能被外部直接访问

typedef struct rex_timer_struct

{

  struct{

    struct rex_timer_struct  *next_ptr;

    struct rex_timer_struct  *prev_ptr;

  }link;

  rex_timer_cnt_type  cnt;  //当前计数值

  rex_tcb_type  *tcb_ptr;  //指向需要信号的TCB结构

  rex_sigs_type  sigs;  //关联的信号量

  #ifdef FEATURE_REX_TIMER_EX

    rex_timer_cb_type  cb_ptr;  //function called when timer expires

    unsigned long  cb_param;  //arguments to callback function

  #endif

}rex_timer_type;

 

1.1.3 临界区(critical section)数据结构

  *提供互斥机制

typedef struct{

  byte  lock_count;  //  >0 if crit sect is taken

  struct rex_tcb_struct  *owner;  //持有者的TCB指针

  struct rex_tcb_struct  *tcb_link;  //等待队列的头指针

  rex_priority_type  orig_pri;  //原始优先级,为支持优先级反转而提供

}rex_crit_sect_type;

 

1.1.4  上下文帧的结构

  *任务的上下文,记录了ARM的各个寄存器的数据

typedef PACKED struct{

  rex_cpu_register_type  spsr;

  rex_cpu_register_type  r[13];  //r0-r7,r8-r12

  rex_cpu_register_type  lr;  //r14

  rex_cpu_register_type  pc;  //r15

}rex_context_frame_type;

 

1.2 几个全局变量

  1.2.1 rex_curr_task

  *当前任务的控制块TCB指针

  rex_tcb_type  *rex_curr_task;

1.2.2 rex_best_task

  *处于ready状态,优先级最高的task

  *将想要成为rex_curr_task的任务设为rex_best_task,再调用rex_sched()进行任务的上下文切换

  *有些情况下,由于任务调度被枷锁,或处于ISR中端模式,rex_sched()不会被马上进行任务切换。因此,在rex_sched()真正进行调度之前,             rex_best_task可能在不同地方被多次更改。所以在确定是否rex_best_task时,应该将需要切换的任务与rex_best_task进行比较(而不是                 rex_curr_task)。只有当改任务处于ready状态,且优先级比rex_best_task更高时,才允许更新rex_best_task

  

  rex_tcb_type  *rex_best_task;

1.2.3  rex_task_list

  *任务链表的头结点

  rex_tcb_type  rex_task_list;

 

1.2.4 rex_num_tasks

  *任务个数

  int rex_num_stasks = 0;

1.2.5 rex_kernel_tcb

  *任务链表的最末位的节点,及其堆栈

  *一般指向Idle task

  static rex_tcb_type rex_nernel_tcb;

  rex_stack_word_type  rex_kernel_stack[REX_KERNEL_STACK_SIZE/sizeof(rex_stack_word_type)];

 

1.2.6 rex_sched_allow

  *任务调度室否加锁的标志

  int rex_sched_allow = TRUE; //turns sched on/off

1.2.7 rex_nest_depth

  *用于支持任务调度的乔涛加锁,记录嵌套层数

  unsigned int rex_nest_depth = 0; //supports nesting of TASKLOCK FREE

1.2.8 rex_timer_list

  *定时器链表的头节点

  static rex_timer_type rex_timer_list;

1.2.9 rex_null_timer

  *空定时器

  *定时器链表的最末尾节点

  static rex_timer_type rex_null_timer;

1.2.10 rex_irq_vector & rex_fiq_vector

  *包含用户定义的ISR中断服务函数的入口点

  void  (*rex_irq_vector)(void);

  void  (*rex_fiq_vector)(void);

1.3 MACROS(几个宏定义)

1.3.1  REX_VERSION_NUMBER

  #define REX_VERION_NUMBER ((unsigned long)403)

1.3.2 任务链表操作宏

  *REX_TASK_LIST_FRONT()  获得任务链表的头结点,多用于链表循环

   *REX_TASK_LIST_NEXT(tcb_ptr)获得指定任务的下一个任务

  * REX_TASK_LIST_PREV(tcb_ptr)获得指定任务的前一个任务

  * REX_TASK_LIST_POP(tcb_ptr)将指定任务从任务链表中移除

   #define REX_TASK_LIST_FRONT()(&rex_task_list)

  #define REX_TASK_LIST_NEXT(tcb_ptr)((rex_tcb_type*)tcb->link.next_ptr)

  #define REX_TASK_LIST_PREV(tcb_ptr)((rex_tcb_type*)tcb_ptr->link.prev_ptr)

 1.3.3 REX_TASK_RUNNABLE(tcb)

  *判断指定任务是否处于ready状态

  *判据: 1.任务是否挂起; 2.任务是否在等待进入临界区 3.任务是否在等待信号量;4.是否有APC队列需要处理

   #define REX_TASK_RUNNABLE(tcb)((tcb->suspended ==FALSE)&&(tcb->cs_link.next_ptr==NULL)&&((tcb->wait == 0)|| (tcb->num_apcs)>0)))

 

  1.3.4 看门狗操作宏

  *REX_PAUSE_DOG_MONITOR(tcb_ptr)通知DOG停止监视该任务

  *REX_RESUME_DOG_MONITOR(tcb_ptr)通知DOG恢复对该任务的监视

  #define REX_PAUSE_DOG_MONITOR(tcb_ptr)\

  {\

    if((tcb_ptr->autodog_enabled)&&(tcb_ptr->dog_report_val>=0))\

    {

      dog_monitor_pause(tcb_ptr->dog_report_val);\

    }\

  }

  #define REX_RESUME_DOG_MONITOR(tcb_ptr)\

  {\

    if(tcb_ptr->dog_report_val>=0)\

    {\

      dog_monitor_resume(tcb_ptr->dog_report_val);\

    }\

  }

2. 任务(TASK)

  REX把task当做一个个独立的入口函数,每个task都拥有各自的堆栈,优先级,这些共同构成了任务的上下文。每个任务都有一个相关联的数据结构,成为TCB(任务控制块)。

  REX允许在执行任意时刻创建任意数目的task。实际上,每增加一个任务,由于遍历更长的任务链表,REX性能会有轻微的下降。需要小心控制任务的数目。

  *任务堆栈:

    每个任务都有用自己的堆栈,在运行时被使用。当任务挂起时(如运行其他任务或进行中断服务),任务的寄存器会被压入任务对战中,并将栈顶指针保存在任务TCB里。等到任务被选中再次运行时,从TCB里获取栈顶指针,将任务的寄存器值从栈顶弹出,任务于是从上次被中断的位置继续运行。这些任务切换的处理对于任务来说是透明的(可以参考【第三章  调度】)

 

2.1 创建任务

  2.1.1 rex_def_task_internal

  定义和创建一个任务

  *定义初始的任务上下文,初始化TCB结构信息

  *将任务按优先级顺序插入到rex_task_list中

  *若是该任务优先级比rex_best_task更高且没有挂起,则进行任务调度

  void rex_def_task_internal(
rex_tcb_type *p_tcb, /* valid tcb for new task */
unsigned char* p_stack, /* stack for new task */
rex_stack_size_type p_stksiz, /* stack size in bytes */
rex_priority_type p_pri, /* priority for new task */
rex_task_func_type p_task, /* task startup function */
dword p_param, /* parameter for new task */
char *p_tskname, /* A/N string for task name */
boolean p_susp, /* is task initially suspended? */
void *p_parent, /* opaque handle to container */
boolean p_dynamic, /* stack/tcb alloc‘d via dyna mem */
int dog_report_val /* Dog report value */
)
{
word index = 0;
byte *stack_ptr = NULL;
rex_context_frame_type *cf_ptr = NULL;
/*-------------------------------------------------------
** Task stack pointer points to the bottom of allocated
** stack memory. p_stksiz is the number of 8-bit bytes.
**-----------------------------------------------------*/
stack_ptr = (byte *)((unsigned long)p_stack + (unsigned long)p_stksiz - sizeof(unsigned long) );
/*-------------------------------------------------------
** Creates room for the context.
** sp points to the top of the context frame.
**-----------------------------------------------------*/
stack_ptr -= sizeof( rex_context_frame_type );

/*-------------------------------------------------------
** Defines the initial context.
** 设置任务的pc、lr为通用任务入口函数rex_task_preamble(),其参数为
** p_task、p_param。
**-----------------------------------------------------*/
cf_ptr = (rex_context_frame_type*)stack_ptr;
cf_ptr->spsr.val = PSR_Supervisor | PSR_Thumb;
cf_ptr->r[0].task = p_task;
cf_ptr->r[1].arg = p_param;
cf_ptr->r[10].arg = (unsigned long)p_stack;
cf_ptr->lr.preamble = rex_task_preamble;
cf_ptr->pc.preamble = rex_task_preamble;
/* ------------------------------------------------------
** Initialize the task control block (TCB)
** ------------------------------------------------------ */
p_tcb->sp = stack_ptr;
p_tcb->stack_limit = p_stack;
p_tcb->stack_size = p_stksiz;
p_tcb->slices = 0;
p_tcb->sigs = 0;
p_tcb->wait = 0;
p_tcb->pri = p_pri;
p_tcb->cs_link.next_ptr = NULL;
p_tcb->cs_link.prev_ptr = NULL;
p_tcb->cs_sp = p_tcb->cs_stack; - -p_tcb->cs_sp;
p_tcb->suspended = p_susp;
#ifdef FEATURE_SI_STACK_WM
rex_swm_init( p_tcb );
#endif /* FEATURE_SI_STACK_WM */
p_tcb->task_name[REX_TASK_NAME_LEN] = ‘\0‘;
if (p_tskname != NULL) /* copy task name if one was supplied */
{
/* copy bytes until /0 received or enough chars have been copied */
while ( (p_tcb->task_name[index] = p_tskname[index] ) &&
( index++ < REX_TASK_NAME_LEN ) );;
}
#if defined FEATURE_REX_APC
p_tcb->num_apcs = 0; /* Number of queued APCs */
#endif

/*-------------------------------------------------------
** Defines the initial context.
** 设置任务的pc、lr为通用任务入口函数rex_task_preamble(),其参数为
** p_task、p_param。
**-----------------------------------------------------*/
cf_ptr = (rex_context_frame_type*)stack_ptr;
cf_ptr->spsr.val = PSR_Supervisor | PSR_Thumb;
cf_ptr->r[0].task = p_task;
cf_ptr->r[1].arg = p_param;
cf_ptr->r[10].arg = (unsigned long)p_stack;
cf_ptr->lr.preamble = rex_task_preamble;
cf_ptr->pc.preamble = rex_task_preamble;
/* ------------------------------------------------------
** Initialize the task control block (TCB)
** ------------------------------------------------------ */
p_tcb->sp = stack_ptr;
p_tcb->stack_limit = p_stack;
p_tcb->stack_size = p_stksiz;
p_tcb->slices = 0;
p_tcb->sigs = 0;
p_tcb->wait = 0;
p_tcb->pri = p_pri;
p_tcb->cs_link.next_ptr = NULL;
p_tcb->cs_link.prev_ptr = NULL;
p_tcb->cs_sp = p_tcb->cs_stack; - -p_tcb->cs_sp;
p_tcb->suspended = p_susp;
#ifdef FEATURE_SI_STACK_WM
rex_swm_init( p_tcb );
#endif /* FEATURE_SI_STACK_WM */
p_tcb->task_name[REX_TASK_NAME_LEN] = ‘\0‘;
if (p_tskname != NULL) /* copy task name if one was supplied */
{
/* copy bytes until /0 received or enough chars have been copied */
while ( (p_tcb->task_name[index] = p_tskname[index] ) &&
( index++ < REX_TASK_NAME_LEN ) );;
}
#if defined FEATURE_REX_APC
p_tcb->num_apcs = 0; /* Number of queued APCs */
#endif

p_tcb->link.prev_ptr = tcb_ptr->link.prev_ptr;
p_tcb->link.next_ptr = tcb_ptr;
tcb_ptr->link.prev_ptr->link.next_ptr = p_tcb;
tcb_ptr->link.prev_ptr = p_tcb;
}
#ifdef FEATURE_REX_IPC
if (ipcns_node_register(p_tcb) == FALSE)
{
return;
}
#endif
/*---------------------------------------------------
** Make this task the best task if it is higher
** priority than the present best task.
**---------------------------------------------------*/
/* Always compare with REX_BEST_TASK, not REX_CURR_TASK */
if ( (p_pri > rex_best_task->pri) && (p_tcb->suspended == FALSE) )
{
rex_best_task = p_tcb;
/* swap the task in */
rex_sched();
}
rex_num_tasks++;
REX_INTFREE();
return;
}

  相关的API: rex_def_task()、rex_def_task_ext()、rex_def_task_ext2()

2.2. 任务的通用引导函数

  2.2.1. rex_task_preamble() 

  *每个新创建的任务在第一次运行时,都会首先执行这个函数。这样做的好处是可以处理任务入口函数返回的情况(在这里,会将该任务直接删除)。

  *只能由REX内部调用

  void rex_task_preamble(
  void (*func_ptr)( dword arg ),
      dword arg
  )

  {
    func_ptr( arg );
    /* if we return, kill the task */
    rex_kill_task( rex_self() );
  } /* END rex_task_preamble */

2.3. 任务挂起和继续

  2.3.1. rex_suspend_task()

  *挂起一个任务,使其不再接受调度

  *如果挂起的是当前任务,则要进行一次任务调度

void rex_suspend_task( rex_tcb_type *p_tcb)
{
p_tcb->suspended = TRUE;
REX_INTLOCK();
if ( ( p_tcb == rex_curr_task ) && !rex_is_in_irq_mode( ) )
{
rex_set_best_task( REX_TASK_LIST_FRONT() );
rex_sched( );
}
REX_INTFREE();
return;
} /* END rex_suspend_task */

  2.3.2. rex_resume_task

  *使任务重新接受调度

  *若该任务优先级比rex_best_task更高,则进行任务调度

void rex_resume_task( rex_tcb_type *p_tcb)
{
REX_INTLOCK();
/* basic sanity check to see if we should even be here or not */
if (p_tcb->suspended == TRUE)
{
p_tcb->suspended = FALSE;
if ((p_tcb->pri > rex_best_task->pri) && REX_TASK_RUNNABLE(p_tcb))
{
rex_best_task = p_tcb;
rex_sched();
}

}
REX_INTFREE();
return;
} /* END rex_resume_task */

2.4. 删除任务

  2.4.1. rex_remove_task

  *将一个任务控制块TCB从任务列表rex_task_list从移除

void rex_remove_task( rex_tcb_type *tcb_ptr /* pointer to tcb */)
{
rex_tcb_type *prev_tcb_ptr;
rex_tcb_type *next_tcb_ptr;
prev_tcb_ptr = REX_TASK_LIST_PREV( tcb_ptr );
next_tcb_ptr = REX_TASK_LIST_NEXT( tcb_ptr );
if ( ( prev_tcb_ptr == NULL ||
prev_tcb_ptr->pri != tcb_ptr->pri ) &&
next_tcb_ptr != NULL &&
next_tcb_ptr->pri == tcb_ptr->pri )
{
/* 若该任务是当前优先级别的代表(最靠前的任务),寻找下一个同一优先级别的任务,作为代表(并未使用) */
rex_tcb_type *temp_tcb_ptr = next_tcb_ptr;
while ( temp_tcb_ptr->pri == tcb_ptr->pri )
{
temp_tcb_ptr->pri_rep_ptr = next_tcb_ptr;
temp_tcb_ptr = REX_TASK_LIST_NEXT( temp_tcb_ptr );
}
}
REX_TASK_LIST_POP( tcb_ptr );
tcb_ptr->link.prev_ptr = NULL;
tcb_ptr->link.next_ptr = NULL;
return;
} /* END rex_remove_task */

  2.4.2. rex_kill_task_ext()

  *首先将任务从rex_task_list从移除

  *移除与其相关的定时器

  *通知DOG停止对其的监视

  *如果持有临界区,则需要释放它

  *如果需要任务调度,先检查该任务是否持有任务调度锁定,若有则需释放锁定,再进行任务调度

void rex_kill_task_ext(
rex_tcb_type *p_tcb,
boolean schedule_new_task
)
{
REX_INTLOCK();
TASKLOCK();
/* Task is alive only if it is still linked into TCB list.
*/
if ( (p_tcb->link.prev_ptr != NULL ) || (p_tcb->link.next_ptr != NULL) )
{
/* Remove TCB from the task list.
*/
rex_remove_task( p_tcb );
/* Remove REX timers associated with the task from the timer list.
*/
rex_delete_task_timers( p_tcb );
/* Tell Dog to stop monitoring this task.
*/
REX_PAUSE_DOG_MONITOR( p_tcb );
/* Check if we were holding or waiting on a critical section */
while (p_tcb->cs_sp >= p_tcb->cs_stack)
{
if ( p_tcb->cs_link.next_ptr == NULL) /* holding crit section */
{
/* free the crit section, but don‘t call rex_sched() yet */
rex_leave_crit_sect_internals( *p_tcb->cs_sp, p_tcb, FALSE);
}
else /* we were waiting on the list */
{
/* if item is first on the list, fix up list head */
if (p_tcb->cs_link.prev_ptr == REX_CRIT_SECT_FLAG)
{
(*p_tcb->cs_sp)->tcb_link = p_tcb->cs_link.next_ptr;
}
else /* fix up previous item on list */

{
p_tcb->cs_link.prev_ptr->cs_link.next_ptr =
p_tcb->cs_link.next_ptr;
}
/* if item is NOT the last on the list */
if (p_tcb->cs_link.next_ptr != REX_CRIT_SECT_FLAG)
{
p_tcb->cs_link.next_ptr->cs_link.prev_ptr =
p_tcb->cs_link.prev_ptr;
}
--p_tcb->cs_sp;
}
} /* END we needed to deal with crit section */
rex_num_tasks--;
if( schedule_new_task )
{
/* 如果任务是想杀死自身,并且持有任务锁定,则要释放任务锁定*/
if (p_tcb == rex_curr_task)
{
if (rex_nest_depth > 0)
{
rex_nest_depth = 0;
rex_sched_allow = TRUE;
}
} /* end-if task was killing itself */
rex_set_best_task( REX_TASK_LIST_FRONT() );
rex_sched();
} /* END needed to reschedule */
} /* END TCB was still in active list */
TASKFREE();
REX_INTFREE();
return;
} /* END rex_kill_task_ext */

  相关的API:rex_kill_task()

2.5. Others

  2.5.1. rex_self()

  *获得当前任务的控制块TCB

rex_tcb_type *rex_self( void )
{
/*-------------------------------------------------------
** The currently running task is in rex_curr_task
**-----------------------------------------------------*/
return rex_curr_task;
} /* END rex_self */

  2.5.2. rex_get_pri()

  *获得当前任务的优先级

rex_priority_type rex_get_pri( void )
{
/*-------------------------------------------------------
** Just return the priority field of the current task
**-----------------------------------------------------*/
return rex_curr_task->pri;
} /* END rex_get_pri */

  2.5.3. rex_set_pri()

  *设置任务的优先级

rex_priority_type rex_set_pri(
rex_priority_type p_pri /* the new priority */
)
{
/*-------------------------------------------------------
** A wrapper function that just calls rex_task_pri with
** the current task
**-----------------------------------------------------*/
return rex_task_pri(rex_curr_task, p_pri);
} /* END rex_set_pri */

  2.5.4. rex_task_pri()

  设置指定任务的优先级

  *从任务链表中移除

  *改变该任务的优先级

  *将该任务按照新优先级插入任务链表中

  *若满足调度条件,则进行任务调度

rex_priority_type rex_task_pri(
rex_tcb_type *p_tcb, /* tcb to set priority on */
rex_priority_type p_pri /* the new priority */
)
{
rex_priority_type prev_pri = p_tcb->pri; /* the priority before the set */
boolean comp = FALSE; /* Comparator */
REX_INTLOCK();
comp = (p_pri == p_tcb->pri);
REX_INTFREE();
/* Return if the priority is the same */
if( comp )
{
return prev_pri;
}
REX_INTLOCK();
/* 先从链表中移除,在根据新优先级将其重新插入到一个新位置 */
p_tcb->link.next_ptr->link.prev_ptr = p_tcb->link.prev_ptr;
p_tcb->link.prev_ptr->link.next_ptr = p_tcb->link.next_ptr;
p_tcb->pri = p_pri;
/* 按照优先级大小,将任务插入任务链表;rex_idle_task(the kernel task)优先级为0,处于链表末尾 */
search_ptr = rex_task_list.link.next_ptr;
while(search_ptr->pri > p_pri) {
search_ptr = search_ptr->link.next_ptr;
}
p_tcb->link.prev_ptr = search_ptr->link.prev_ptr;
p_tcb->link.next_ptr = search_ptr;
search_ptr->link.prev_ptr->link.next_ptr = p_tcb;
search_ptr->link.prev_ptr = p_tcb;
/* 如果任务处于ready状态,且优先级比rex_best_task更高,则进行任务切换 */
if ( (p_pri > rex_best_task->pri) && ( REX_TASK_RUNNABLE(p_tcb) ) )
{

rex_best_task = p_tcb;
rex_sched();
}
REX_INTFREE();
return prev_pri;
} /* END rex_task_pri */

3. 调度(Schedule)

  REX使用基于优先级的调度算法。每个任务都有一个32位非零的正整数作为其优先级,优先级越高、数字越大,优先级0保留给kernel task(即idle task)使用。老版本的REX要求每个任务的优先级是唯一的,现在的版本中无此限制。
  在任务调度时,REX总是选择优先级最高的ready状态的任务——优先级最高且不等待任何事件的任务。如果选择不唯一,REX在其中任意选择一个。被选中的任务将会开始运行,直到它自愿挂起,或者中断激活了一个更高优先级的任务。
  当一个被挂起的任务所等待的条件被满足时,任务将会进入ready状态。当所以任务被挂起时,idle任务将会执行。
REX还提供了机制,允许任务改变自身或其他任务的优先级。

 

3.1. 调度代码

  3.1.1. rex_sched()

  *执行实际上的任务切换工作

  *只能被REX内核函数调用,不能由用户调用

  *典型地,在一个REX服务改变了best task指针后被调用

  *rex_sched()首先判断current task和best task是否相同。若相同,则直接返回;否则,将best task赋值给current task。再查看当前处于任务级还是中断级,若是任务级,则保存旧任务的上下文,载入新任务的上下文;若是中断级,则不会执行上下文切换,而是会等到返回到任务级后再执行

LEAF_NODE rex_sched
mrs a3, CPSR ; Save the CPSR for later.
orr a1, a3, #PSR_Irq_Mask:OR:PSR_Fiq_Mask禁止FIQ中断
msr CPSR_c, a1
;---------------------------------------------------------------------------
; 如果当前处于中断状态,就返回
;---------------------------------------------------------------------------
and a1, a3, #PSR_Mode_Mask
cmp a1, #PSR_Supervisor ; If not in Supervisor mode do not swap
bne rex_sched_exit_1 ; until we revert back to task level
;---------------------------------------------------------------------------
; 如果任务调度被加锁,也返回
;---------------------------------------------------------------------------
; test for TASKLOCK
ldr a2, =rex_sched_allow ; load scheduling flag
ldr a2, [a2] ; dereference sched. flag
cmp a2, #0 ; compare with FALSE
beq rex_sched_exit_1 ; return
;---------------------------------------------------------------------------
; 只有当rex_best_task不等于rex_curr_task才进行任务切换
;---------------------------------------------------------------------------
ldr a2, =rex_best_task ; load the best task into a2
ldr a2, [a2] ; dereference best task
ldr a4, =rex_curr_task ; load the current task into a4
ldr a1, [a4] ; dereference current task
cmp a2, a1 ; if current task == best task just return
beq rex_sched_exit_1
;---------------------------------------------------------------------------
; Set the curr_task to the new value
;---------------------------------------------------------------------------
str a2, [a4] ; set rex_curr_task=rex_best_task
mov a4, a1 ; a4 points now to the last (former current) task
;---------------------------------------------------------------------------
; Increment the slice count.
;---------------------------------------------------------------------------
ldr a1, [a2, #REX_TCB_SLICES_OFFSET] ; load up the slice count
add a1, a1, #1 ; increment it
str a1, [a2, #REX_TCB_SLICES_OFFSET] ; store it
; --------------------------------------------------------------------
; 保存CPU可能被破坏的上下文
; --------------------------------------------------------------------
stmfd sp!, {lr} ; Return address.
sub sp, sp, #8 ; no need to store r12,r14 in task context.
stmfd sp!, {r4-r11}
sub sp, sp, #16 ; Subtract a1-a4 location
stmfd sp!, {a3} ; First line on rex_sched saves CPSR in a3!!!
;---------------------------------------------------------------------------
; Save the context on stack
;---------------------------------------------------------------------------
str sp, [a4, #REX_TCB_STACK_POINTER_OFFSET]
mov a1, a2 ; a1 = the current task
;---------------------------------------------------------------------------
; rex_start_task_1 是函数void rex_start_task(rex_tcb_type *)的入口地址
; 它默认当前a1 为当前任务rex_curr_task的TCB指针
;---------------------------------------------------------------------------
rex_start_task_1
; --------------------------------------------------------------------
; Restore the user state, note this may not be the state saved above
; since the call the rex_sched may have changed which stack the handler isworking on. Note, a context switch will happen here.
; --------------------------------------------------------------------
ldr sp, [a1, #REX_TCB_STACK_POINTER_OFFSET] ; Load thestack pointer
ldmfd sp!, {a1} ; Restore SPSR (in a1)
msr SPSR_f, a1 ; Load SPSR
msr SPSR_c, a1 ; Load SPSR
mov a1, sp ; Load sp in a1.
add sp, sp, #REX_CF_SIZE - 4 ; adjust sp
ldmfd a1, {r0-r12,lr,pc}^ ; Load and return, sp already adjusted.
; --------------------------------------------------------------------
; 如果没有进行上下文切换,由此处退出
; --------------------------------------------------------------------
rex_sched_exit_1
msr CPSR_f, a3 ; Restore interrupts as prior to rex_sched
msr CPSR_c, a3 ; Restore interrupts as prior to rex_sched
LEAF_NODE_END
; END rex_sched

 

3.2. 设定rex_best_task

  rex_best_task表示当前系统中处于ready状态、优先级最高的任务。 

void rex_set_best_task(rex_tcb_type *start_tcb)
{
rex_tcb_type *candidate_task;
ASSERT( start_tcb != NULL );
candidate_task = start_tcb->link.next_ptr;
ASSERT( candidate_task != NULL );
/* find first runnable task */
while ( REX_TASK_RUNNABLE(candidate_task) == FALSE)
{
candidate_task = candidate_task->link.next_ptr;
ASSERT( candidate_task != NULL );
}
rex_best_task = candidate_task;
return;
} /* END rex_set_best_task */ 

3.2.1. rex_set_best_task()

  *遍历任务链表,搜索处于ready状态的任务中优先级最高的,将其设为rex_best_task

3.3. 任务调度加锁/解锁

  3.3.1. rex_task_lock()

  *如果处于IRQ中断模式,禁止加锁,直接推出

  *关中断

  *设置调度允许标志为FALSE,嵌套层数加一

  *开中断

  void rex_task_lock( void )
  {
    if ( !rex_is_in_irq_mode( ) )
    {
      REX_INTLOCK();
      rex_sched_allow = FALSE;
      rex_nest_depth++;
      REX_INTFREE();
    }
  } /* END rex_task_lock */

  相关宏定义:REX_INTLOCK()、INTLOCK()

 

3.3.2. rex_task_free()

  *如果处于IRQ中断模式,禁止解锁,直接推出

  *关中断

  *嵌套次数减一;若减至0,则重新允许调度,并且立即调用rex_sched()进行调度

  *开中断

  void rex_task_free( void )
  {
    if ( !rex_is_in_irq_mode( ) )
    {
      REX_INTLOCK();
      if (rex_nest_depth > 0)
        rex_nest_depth--;
      if (rex_nest_depth == 0)
      {
        rex_sched_allow = TRUE;
        rex_sched();
      }
      REX_INTFREE();
    }
  } /* END rex_task_free */

  *相关宏定义:REX_INTFREE()、INTFREE()

3.3.3. rex_tasks_are_locked()

  *若允许任务调度,返回TRUE;否则,返回FALSE

  int rex_tasks_are_locked( void )
  {
    return !rex_sched_allow;
  } /* END rex_tasks_are_locked */

 

4. 中断(Interrupts)

  REX实现了一个抢先式的内核。从中断处理程序返回时,控制权会交给优先级最高、处于ready状态的任务,而并非一定会返回被中断的任务。

  *Programmable Interrupt Controller(PIC,可编程中断控制器)

  *PIC TRAMPOLINE SERVICES

  4.1. 设置中断向量

  4.1.1. rex_set_interrupt_vector ()

    *设置用户定义的ISR中断服务程序(包括IRQ、FIQ)的入口函数,当指定的中断发生时,该入口函数会被调用

    *用户程序一般不直接调用该接口设置中断,而是通过下面提到的tramp_set_isr()来设置

  void rex_set_interrupt_vector (
      rex_vect_type v, /* Vector */
      void (*fnc_ptr)( void ) /* *function to be installed */
      )
   {
      if (v == P_IRQ_VECT)
      {
        rex_irq_vector = fnc_ptr;
      }
      else
      {
        rex_fiq_vector = fnc_ptr;
      }
  } /* END rex_set_interrupt_vector */

 

4.2. PIC Trampoline Service(可编程控制弹簧中断服务)

  4.2.1. tramp_init()

  *设置ISR的默认值

  *初始化PIC硬件

  *设置tramp_isr()作为IRQ的用户处理函数入口。中断一发生,该函数就将会被调用

  void tramp_init( void )
  {
    uint8 i;
    /* all isr to default */
    for ( i = 0; i < TRAMP_NUM_INTS; i++ )
    {
      isr_func_tbl[i].isr_ptr = tramp_default_isr;
    }
    /* init hardware */
    tramp_init_hardware();

  #ifdef FEATURE_TRAMP_QUEUED_CALLS
   /* Initialize the interrupt call queue.
    */
    (void) q_init( &tramp_call_q );
  #endif /* FEATURE_TRAMP_QUEUED_CALLS */
    /* 将tramp_isr()设置为IRQ ISR,这样每次IRQ中断发生,该函数都将被调用 */
    /* no FIQ ISR for now */
    rex_set_interrupt_vector( P_IRQ_VECT, tramp_isr );
  } /* end tramp_init */

 

4.2.2. tramp_set_isr()

  *用于为一个特别的中断源设置相应的ISR(中断服务函数)

  void tramp_set_isr
  (
    /* 要设置的中断类型 */
    tramp_isr_type int_num,
    /* ISR to be installed for this interrupt */
    isr_ptr_type isr_ptr
  )
  {
      /* Address of priority register corresponding to this interrupt */
    uint32 prio_address;
      /* Address of the Enable registers: IRQ_ENABLE_0 and IRQ_ENABLE_1 */
    uint32 mask_reg_address;
      /* Address of the Clear registers: IRQ_ENABLE_0 and IRQ_ENABLE_1 */
    uint32 clear_reg_address;
      /* Interrupt mask to set in the enable register */
    uint32 mask_val;
      /* Mask to clear bit in the CLEAR register */
    uint32 clear_val = 0;
      /* disable interrupts while changing table and PIC registers */
    INTLOCK();
      /* ISR if passed-in ISR is NULL, change it to tramp_default_isr */
    if (isr_ptr == NULL)
    {
      isr_ptr = tramp_default_isr;

    }

    /* load our local table with the function ptr */
isr_func_tbl[int_num].isr_ptr = isr_ptr;
/* 将优先级写入PIC的优先级寄存器。优先级寄存器为32位,从PRIO_BASE地址开始,按照中断编号排序。因此,我们可以将中断编号乘以4来获得中断的优先级寄存器地址 */
prio_address = PRIO_BASE + ((unsigned int)int_num << 2);
outpdw( prio_address, (uint32) (isr_func_tbl[int_num].priority & MAX_PRIO_VAL));
/* 确定需要修改的是哪一个中断屏蔽寄存器mask register */
if ( int_num >= NUM_INT_BITS_IN_REG)
{
mask_reg_address = HWIO_ADDR(IRQ_ENABLE_1);
mask_val = HWIO_IN(IRQ_ENABLE_1);
clear_reg_address= HWIO_ADDR(IRQ_CLEAR_1);
/* convert to bit offset in register */
int_num -= NUM_INT_BITS_IN_REG;
}
else
{
mask_reg_address = HWIO_ADDR(IRQ_ENABLE_0);
mask_val = HWIO_IN(IRQ_ENABLE_0);
clear_reg_address= HWIO_ADDR(IRQ_CLEAR_0);
}
/* 将相应的bit置位或复位 */
if (isr_ptr == tramp_default_isr)
{
mask_val &= ~((unsigned int)1 <<int_num); /* set that bit to zero, turning off INT */
/* clear the status bit of this interrupt */
clear_val = (1 << int_num);
}
else
{
mask_val |= ((unsigned int)1 << int_num); /* set bit to one, turning on INT */
}

/* 写入中断屏蔽寄存器mask register */
outpdw( mask_reg_address, mask_val);
/* 考虑到中断可能在清空状态位时发生,我们在最后清空中断状态寄存器status register。This is because INT STATUS = INT ENABLE MASK & INT_SRC(s) */
  if (isr_ptr == tramp_default_isr)
  {
  /* unset bit in the CLEAR register => clears bit in STATUS register */
  outpdw( clear_reg_address, clear_val );
  }
  INTFREE();
  } /* end tramp_set_isr */

 

4.2.3. tramp_isr()

  *IRQ中断发生时,该函数将会被调用(可以参见下面的IRQ_handler)

  *程序反复读取PIC中的IRQ_VEC_INDEX_RD,根据寄存器的返回值跳转执行相应的ISR。直到寄存器返回NON_VECTOR,表示已经没有被挂起的中  

   断了

  *在如下两种情况,IRQ_ENABLE寄存器的相应位会被复位:

    1) 在调用ISR前复位

    2) 在ISR调用之后复位。在这种情况下,我们不能仅仅关中断并调用ISR,

    void tramp_isr( )
{
/* vector index from PIC register */
uint32 vect_idx;
/* for our local tbl */
uint32 tbl_idx;
/* Mask of the occurring interrupt */
uint32 mask_val;
/* Address of the IRQ_ENABLE register */
uint32 mask_reg_address;
/* Address of the IRQ_CLEAR register */
uint32 clear_reg_address;
/*注意:有两种情况会读取IRQ_VEC_INDEX_RD寄存器。
第一种是当ARM中断时,tramp_isr()被调用时会读取;
第二种是在我们处理完ISR后会读取。这取决于是否还有被挂起的中断*/
/* 该变量决定我们所读取的状态值,是来自于ARM中断、还是在执行完ISR之后。
在上述两种模式下,我们读取不同的寄存器来确定发生的是哪一个中断。
IRQ_VEC_INDEX_RD:ARM中断时读取,返回最高优先级中断的索引;
IRQ_VEC_INDEX_PEND_RD:处理完中断时读取,返回被挂起的最高优先级的中
断、或NON_VECTOR表示没有中断被挂起。*/
boolean irq_from_arm = TRUE;

#ifdef FEATURE_DEBUG_TRAMP_EXECUTION
TRAMP_DEBUG_IN_ISR = 1;
#endif
/* 假设-这里假设我们在进入前已关了中断-这样的假设确实有效*/
for (;;) /* forever */
{
if (irq_from_arm)
{
/* IRQ_VEC_INDEX_RD 包含了当前最高优先级的中断向量的索引值。为了实现
“smart function”(不用在TASK和IRQ模式间来回切换,就可以处理多个中断),
我们不停的读取该寄存器,直至返回一个标志值。
注意读取寄存器会通知PIC我们已经处理完了上一次读取的ISR。所以,我们不能随意
读取该寄存器-除非我们已经处理完了上一个ISR。*/
tbl_idx = vect_idx = HWIO_INM(IRQ_VEC_INDEX_RD, IRQ_VEC_INDEX_RD_RMSK );
irq_from_arm = FALSE;
#ifdef FEATURE_TRAMP_QUEUED_CALLS
nested_int_cnt++;
#endif
}
else
{
/* Lock interrupt before reading index register */
(void) rex_int_lock();
tbl_idx = vect_idx = HWIO_INM(IRQ_VEC_INDEX_PEND_RD,
IRQ_VEC_INDEX_PEND_RD_RMSK);
}
/* 确定是否还有被挂起的中断。如果没有,会返回NON_VECTOR。 */
if (vect_idx == NON_VECTOR)
{
/* No more interrupt to process for the time being.
*/
#ifdef FEATURE_TRAMP_QUEUED_CALLS
/* Since everything else is done, handle queued calls
*/
if (nested_int_cnt == 1)
{
tramp_call_ptr_type *call_ptr;
/* 只有当没有需要处理的中断时,才允许处理队列调用 */
while ( (call_ptr = (tramp_call_ptr_type *) q_get( &tramp_call_q )) !=

NULL )
{
/* 通过call_ptr结构中的指针来调用函数,并将call_ptr中保存的参数传给它*/
if (call_ptr->call_ptr)
{
#ifdef FEATURE_DEBUG_TRAMP_EXECUTION
TRAMP_DEBUG_IN_ISR_QUEUED_CALL = 1;
/*save call for debugging*/
TRAMP_DEBUG_QUEUED_CALL_FUNC_PTR = (void*) call_ptr->call_ptr;
#endif
(void) rex_int_free();
(*(call_ptr->call_ptr))( call_ptr->arg.arg_int4, call_ptr->arg.arg_ptr );
(void) rex_int_lock();
call_ptr->in_use = FALSE;
#ifdef FEATURE_DEBUG_TRAMP_EXECUTION
TRAMP_DEBUG_IN_ISR_QUEUED_CALL = 0;
#endif
}
else
{
ERR_FATAL("Invalid call_ptr in tramp_handle_int_calls", 0, 0, 0);
}
}
}
/* 为了避免在我们正处理调用时,另一个中断到来与之发生竞争,需要等到调用处理完成后减一。只需要一个ISR实例来处理调用。 */
nested_int_cnt--;
#endif /* FEATURE_TRAMP_QUEUED_CALLS */
#ifdef FEATURE_DEBUG_TRAMP_EXECUTION
if (nested_int_cnt==0)
{
/*all isrs finished*/
TRAMP_DEBUG_IN_ISR = 0;
}
#endif

return;
}
/* 此时,我们实际上还在执行ISR,即使并不在ISR主函数中。开中断以允许抢先 */
(void) rex_int_free();
/* determine which clear register to write to */
if ( vect_idx >= NUM_INT_BITS_IN_REG)
{
clear_reg_address = HWIO_ADDR(IRQ_CLEAR_1);
mask_reg_address = HWIO_ADDR(IRQ_ENABLE_1);
/* adjust bit offset if it‘s in different register */
vect_idx -= NUM_INT_BITS_IN_REG;
}
else
{
clear_reg_address = HWIO_ADDR(IRQ_CLEAR_0);
mask_reg_address = HWIO_ADDR(IRQ_ENABLE_0);
}
/* 两种不同的情况,我们清除中断寄存器标志位的时机不同 */
#ifdef FEATURE_DEBUG_TRAMP_EXECUTION
TRAMP_DEBUG_ISR_NUM = tbl_idx;
#endif
/* Case 1. 在调用ISR之前清除 */
if ( isr_func_tbl[tbl_idx].clr_when == CLR_BEF)
{
outpdw( clear_reg_address, (1 << vect_idx) ); /* clear the int */
#ifdef TIMETEST
TIMETEST_ISR_ID( isr_func_tbl[tbl_idx].id );
#endif
if (isr_func_tbl[tbl_idx].isr_ptr==NULL)
{
ERR_FATAL("NULL ISR ptr",0,0,0);
}
(isr_func_tbl[tbl_idx].isr_ptr) (); /* call the registered ISR */
}
/* case 2. 在调用ISR之后清除 */
else

{
#ifdef TIMETEST
TIMETEST_ISR_ID( isr_func_tbl[tbl_idx].id );
#endif
if (isr_func_tbl[tbl_idx].isr_ptr==NULL)
{
ERR_FATAL("NULL ISR ptr",0,0,0);
}
/* 在此,真正调用已注册的ISR开始中断服务 */
(isr_func_tbl[tbl_idx].isr_ptr) ();
/* clear the bit */
outpdw( clear_reg_address, (1 << vect_idx) );
}
} /* end for(;;) */
} /* end tramp_isr */

 

4.3. IRQ_handler

  IRQ中断服务入口

REX系统2

标签:mic   val   disable   resume   void   中断处理程序   led   等待队列   super   

原文地址:http://www.cnblogs.com/zxc2man/p/7683845.html

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