/*
*********************************************************************************************************
*                                                uC/OS-II
*                                          The Real-Time Kernel
*                                  MUTUAL EXCLUSION SEMAPHORE MANAGEMENT
*
*                          (c) Copyright 1992-2002, Jean J. Labrosse, Weston, FL
*                                           All Rights Reserved
*
* File : OS_MUTEX.C
* By   : Jean J. Labrosse

* 翻譯： likee
                                            互斥型信號(hào)量管理
*********************************************************************************************************
*/

#ifndef  OS_MASTER_FILE
#include "includes.h"
#endif

/*
*********************************************************************************************************
*                                            LOCAL CONSTANTS
*********************************************************************************************************
*/

#define  OS_MUTEX_KEEP_LOWER_8   0x00FF
#define  OS_MUTEX_KEEP_UPPER_8   0xFF00

#define  OS_MUTEX_AVAILABLE      0x00FF


#if OS_MUTEX_EN > 0
/*
*********************************************************************************************************
*                                   ACCEPT MUTUAL EXCLUSION SEMAPHORE
*
* Description: This  function checks the mutual exclusion semaphore to see if a resource is available.
*              Unlike OSMutexPend(), OSMutexAccept() does not suspend the calling task if the resource is
*              not available or the event did not occur.
*
* Arguments  : pevent     is a pointer to the event control block
*
*              err        is a pointer to an error code which will be returned to your application:
*                            OS_NO_ERR          if the call was successful.
*                            OS_ERR_EVENT_TYPE  if 'pevent' is not a pointer to a mutex
*                            OS_ERR_PEVENT_NULL 'pevent' is a NULL pointer
*                            OS_ERR_PEND_ISR     if you called this function from an ISR
*
* Returns    : == 1       if the resource is available, the mutual exclusion semaphore is acquired
*              == 0       a) if the resource is not available
*                         b) you didn't pass a pointer to a mutual exclusion semaphore
*                         c) you called this function from an ISR
*
* Warning(s) : This function CANNOT be called from an ISR because mutual exclusion semaphores are
*              intended to be used by tasks only.
*********************************************************************************************************
*/

#if OS_MUTEX_ACCEPT_EN > 0
INT8U  OSMutexAccept (OS_EVENT *pevent, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                            /* Allocate storage for CPU status register     */
    OS_CPU_SR  cpu_sr;
#endif    
    
    
    if (OSIntNesting > 0) {                            /* Make sure it's not called from an ISR        */
        *err = OS_ERR_PEND_ISR;
        return (0);
    }
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                     /* Validate 'pevent'                            */
        *err = OS_ERR_PEVENT_NULL;
        return (0);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) {  /* Validate event block type                    */
        *err = OS_ERR_EVENT_TYPE;
        return (0);
    }
#endif                                                     
    OS_ENTER_CRITICAL();							   /* Get value (0 or 1) of Mutex                  */
    if ((pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8) == OS_MUTEX_AVAILABLE) {     
        pevent->OSEventCnt &= OS_MUTEX_KEEP_UPPER_8;   /*      Mask off LSByte (Acquire Mutex)         */
        pevent->OSEventCnt |= OSTCBCur->OSTCBPrio;     /*      Save current task priority in LSByte    */
        pevent->OSEventPtr  = (void *)OSTCBCur;        /*      Link TCB of task owning Mutex           */
        OS_EXIT_CRITICAL();
        *err = OS_NO_ERR;
        return (1);
    }
    OS_EXIT_CRITICAL();
    *err = OS_NO_ERR;
    return (0);
}
#endif                                                     

/*$PAGE*/
/*
*********************************************************************************************************
*                                  CREATE A MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function creates a mutual exclusion semaphore.
*
* Arguments  : prio          is the priority to use when accessing the mutual exclusion semaphore.  In
*                            other words, when the semaphore is acquired and a higher priority task
*                            attempts to obtain the semaphore then the priority of the task owning the
*                            semaphore is raised to this priority.  It is assumed that you will specify
*                            a priority that is LOWER in value than ANY of the tasks competing for the
*                            mutex.
*
*              err           is a pointer to an error code which will be returned to your application:
*                               OS_NO_ERR           if the call was successful.
*                               OS_ERR_CREATE_ISR   if you attempted to create a MUTEX from an ISR
*                               OS_PRIO_EXIST       if a task at the priority inheritance priority
*                                                   already exist.
*                               OS_ERR_PEVENT_NULL  No more event control blocks available.
*                               OS_PRIO_INVALID     if the priority you specify is higher that the 
*                                                   maximum allowed (i.e. > OS_LOWEST_PRIO)
*
* Returns    : != (void *)0  is a pointer to the event control clock (OS_EVENT) associated with the
*                            created mutex.
*              == (void *)0  if an error is detected.
*
* Note(s)    : 1) The LEAST significant 8 bits of '.OSEventCnt' are used to hold the priority number
*                 of the task owning the mutex or 0xFF if no task owns the mutex.
*              2) The MOST  significant 8 bits of '.OSEventCnt' are used to hold the priority number
*                 to use to reduce priority inversion.
                                                     建立一個(gè)互斥型信號(hào)量
描述：建立一個(gè)互斥型信號(hào)量
參數(shù)：prio：當(dāng)存取互斥型信號(hào)量時(shí)它的優(yōu)先級(jí)。就是說，當(dāng)任務(wù)需要信號(hào)量，
                     而另一優(yōu)先級(jí)更高的任務(wù)想得到信號(hào)量，就改變當(dāng)前任務(wù)的優(yōu)先級(jí)，變?yōu)楦?                     假定你改變的優(yōu)先級(jí)值小于任務(wù)競(jìng)爭(zhēng)這個(gè)信號(hào)量的任務(wù)的值（即優(yōu)先級(jí)更高）
                 err:應(yīng)用時(shí)包含錯(cuò)誤代碼的指針 ：
*                               OS_NO_ERR          調(diào)用成功
*                               OS_ERR_CREATE_ISR   如果想從ISR中建立
*                               OS_PRIO_EXIST       如果優(yōu)先級(jí)繼承優(yōu)先級(jí)的優(yōu)先級(jí)已經(jīng)存在
*                               OS_ERR_PEVENT_NULL  沒有事件控制塊可用
*                               OS_PRIO_INVALID    如果你指定的優(yōu)先級(jí)大于最大值

*********************************************************************************************************
*/

OS_EVENT  *OSMutexCreate (INT8U prio, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
    OS_CPU_SR  cpu_sr;
#endif    
    OS_EVENT  *pevent;


    if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
        *err = OS_ERR_CREATE_ISR;                          /* ... can't CREATE mutex from an ISR       */
        return ((OS_EVENT *)0);
    }//不能從ISR中建立，不允許在ISR中調(diào)用此函數(shù)
#if OS_ARG_CHK_EN > 0
    if (prio >= OS_LOWEST_PRIO) {                          /* Validate PIP                             */
        *err = OS_PRIO_INVALID;
        return ((OS_EVENT *)0);
    }//不合理的PIP
#endif
    OS_ENTER_CRITICAL();
    if (OSTCBPrioTbl[prio] != (OS_TCB *)0) {               /* Mutex priority must not already exist    */
		//確認(rèn)PIP沒有被任何任務(wù)占用。OSTCBPrioTbl[ ]中的一個(gè)指向NULL的空指針指示
		//PIP有效
        OS_EXIT_CRITICAL();                                /* Task already exist at priority ...       */
        *err = OS_PRIO_EXIST;                              /* ... inheritance priority                 */
		//如果優(yōu)先級(jí)存在 ，則出錯(cuò)。
        return ((OS_EVENT *)0);                            
    }
    OSTCBPrioTbl[prio] = (OS_TCB *)1;                      /* Reserve the table entry                  */
	//置非空指針，將這個(gè)優(yōu)先級(jí)保留下來。
    pevent             = OSEventFreeList;                  /* Get next free event control block        */
	//從空余ECB中得到一塊空的ECB。
    if (pevent == (OS_EVENT *)0) {                         /* See if an ECB was available              */
		//看ECB是否可用
        OSTCBPrioTbl[prio] = (OS_TCB *)0;                  /* No, Release the table entry              */
		//如果不可用，釋放此優(yōu)先級(jí)表入口
        OS_EXIT_CRITICAL();
        *err               = OS_ERR_PEVENT_NULL;           /* No more event control blocks             */
        return (pevent);
    }
    OSEventFreeList     = (OS_EVENT *)OSEventFreeList->OSEventPtr;   /* Adjust the free list           */
	//如果可用，重新調(diào)整事件控制塊的表頭
    OS_EXIT_CRITICAL();
    pevent->OSEventType = OS_EVENT_TYPE_MUTEX;//將其標(biāo)記為互斥型信號(hào)量
    pevent->OSEventCnt  = (prio << 8) | OS_MUTEX_AVAILABLE;/* Resource is available                    */
	//mutex為有效值，同時(shí)將PIP保存起來。值得注意的是，事件計(jì)數(shù)器.OSEventCnt
    //在此處的用法不同，高八位用于保存PIP的值，低侂位在資源無任務(wù)占用
    //時(shí)的值為0xff，有任務(wù)占用時(shí)為占用mutex任務(wù)的優(yōu)先級(jí)。這個(gè)避免了增加額
    //外的空間，節(jié)約對(duì)RAM的占用量
    pevent->OSEventPtr  = (void *)0;                       /* No task owning the mutex       */
	//消息正在初始化，所以沒有等待這個(gè)mutex的任務(wù)
    OS_EventWaitListInit(pevent);//初始化事件等待列表
    *err                = OS_NO_ERR;
    return (pevent);
}

/*$PAGE*/
/*
*********************************************************************************************************
*                                          DELETE A MUTEX
*
* Description: This function deletes a mutual exclusion semaphore and readies all tasks pending on the it.
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired mutex.
*
*              opt           determines delete options as follows:
*                            opt == OS_DEL_NO_PEND   Delete mutex ONLY if no task pending
*                            opt == OS_DEL_ALWAYS    Deletes the mutex even if tasks are waiting.
*                                                    In this case, all the tasks pending will be readied.
*
*              err           is a pointer to an error code that can contain one of the following values:
*                            OS_NO_ERR               The call was successful and the mutex was deleted
*                            OS_ERR_DEL_ISR          If you attempted to delete the MUTEX from an ISR
*                            OS_ERR_INVALID_OPT      An invalid option was specified
*                            OS_ERR_TASK_WAITING     One or more tasks were waiting on the mutex
*                            OS_ERR_EVENT_TYPE       If you didn't pass a pointer to a mutex
*                            OS_ERR_PEVENT_NULL      If 'pevent' is a NULL pointer.
*