ucos中OSMemXX分析-----指向指针的的指针--强制转换

下面8行代码的含义是什么:

#define nblks 10

#define blksize 20

INT8U *pblk; void **plink;

INT8U addr[200];

    plink = (void **)addr;/* Create linked list of free memory blocks */    pblk  = (INT8U *)((INT32U)addr + blksize);    for (i = 0; i < (nblks - 1); i++) {       *plink = (void *)pblk;/* Save pointer to NEXT block in CURRENT block*/        plink = (void **)pblk;/* Position to  NEXT  block */        pblk  = (INT8U *)((INT32U)pblk + blksize);/*Point to the FOLLOWING block*/    }    *plink= (void *)0; /* Last memory block points to NULL*/

 

看得懂的是高手,看不懂的是菜鸟,

看不懂的看下面的使用实例

 

 

 

 

 

 

 

////////////////代码来源

static OS_MEM *pUartMem;static INT8U  UartBuf[UartMsgNum][UartMsgBufLengh];//使用方法:初始化,把内存pUartMem=OSMemCreate(UartBuf,UartMsgNum,UartMsgBufLengh,&err);//Create a mem for Uart post Msg//得到从管理的多段内存中得到一个空闲的固定长度内存pUartBuf=OSMemGet(pUartMem,&err);//Reqire a Mem for Msg//使用完以后释放这个使用的内存.OSMemPut(pUartMem,pUartMsg);

//////////////////////////////////////////////////////////////////////////////////////////////

//函数代码

/***********************************************************************************************************                                        CREATE A MEMORY PARTITION** Description : Create a fixed-sized memory partition that will be managed by uC/OS-II.** Arguments   : addr     is the starting address of the memory partition**               nblks    is the number of memory blocks to create from the partition.**               blksize  is the size (in bytes) of each block in the memory partition.**               err      is a pointer to a variable containing an error message which will be set by*                        this function to either:**                        OS_NO_ERR            if the memory partition has been created correctly.*                        OS_MEM_INVALID_ADDR  you are specifying an invalid address for the memory*                                             storage of the partition or, the block does not align*                                             on a pointer boundary*                        OS_MEM_INVALID_PART  no free partitions available*                        OS_MEM_INVALID_BLKS  user specified an invalid number of blocks (must be >= 2)*                        OS_MEM_INVALID_SIZE  user specified an invalid block size*                                                - must be greater than the size of a pointer*                                                - must be able to hold an integral number of pointers* Returns    : != (OS_MEM *)0  is the partition was created*              == (OS_MEM *)0  if the partition was not created because of invalid arguments or, no*                              free partition is available.**********************************************************************************************************/OS_MEM  *OSMemCreate (void *addr, INT32U nblks, INT32U blksize, INT8U *err){    OS_MEM    *pmem;    INT8U     *pblk;    void     **plink;    INT32U     i;#if OS_CRITICAL_METHOD == 3                           /* Allocate storage for CPU status register      */    OS_CPU_SR  cpu_sr = 0;#endif#if OS_ARG_CHK_EN > 0                  if (err == (INT8U *)0) {                          /* Validate 'err'                                */        return ((OS_MEM *)0);    }    if (addr == (void *)0) {                          /* Must pass a valid address for the memory part.*/        *err = OS_MEM_INVALID_ADDR;        return ((OS_MEM *)0);    }    if (((INT32U)addr & (sizeof(void *) - 1)) != 0){  /* Must be pointer size aligned                  */        *err = OS_MEM_INVALID_ADDR;        return ((OS_MEM *)0);    }    if (nblks < 2) {                                  /* Must have at least 2 blocks per partition     */        *err = OS_MEM_INVALID_BLKS;        return ((OS_MEM *)0);    }    if (blksize < sizeof(void *)) {                   /* Must contain space for at least a pointer     */        *err = OS_MEM_INVALID_SIZE;        return ((OS_MEM *)0);    }    if ((blksize % sizeof(void *)) != 0) {            /* Must contain space for an integral number ... */        *err = OS_MEM_INVALID_SIZE;                   /* ... of pointer sized items                    */        return ((OS_MEM *)0);    }#endif    OS_ENTER_CRITICAL();    pmem = OSMemFreeList;                             /* Get next free memory partition                */    if (OSMemFreeList != (OS_MEM *)0) {               /* See if pool of free partitions was empty      */        OSMemFreeList = (OS_MEM *)OSMemFreeList->OSMemFreeList;    }    OS_EXIT_CRITICAL();    if (pmem == (OS_MEM *)0) {                        /* See if we have a memory partition             */        *err = OS_MEM_INVALID_PART;        return ((OS_MEM *)0);    }    plink = (void **)addr;                            /* Create linked list of free memory blocks      */    pblk  = (INT8U *)((INT32U)addr + blksize);    for (i = 0; i < (nblks - 1); i++) {       *plink = (void *)pblk;                         /* Save pointer to NEXT block in CURRENT block   */        plink = (void **)pblk;                        /* Position to  NEXT      block                  */        pblk  = (INT8U *)((INT32U)pblk + blksize);    /* Point to the FOLLOWING block                  */    }    *plink              = (void *)0;                  /* Last memory block points to NULL              */    pmem->OSMemAddr     = addr;                       /* Store start address of memory partition       */    pmem->OSMemFreeList = addr;                       /* Initialize pointer to pool of free blocks     */    pmem->OSMemNFree    = nblks;                      /* Store number of free blocks in MCB            */    pmem->OSMemNBlks    = nblks;    pmem->OSMemBlkSize  = blksize;                    /* Store block size of each memory blocks        */    *err                = OS_NO_ERR;    return (pmem);}/*$PAGE*//***********************************************************************************************************                                          GET A MEMORY BLOCK** Description : Get a memory block from a partition** Arguments   : pmem    is a pointer to the memory partition control block**               err     is a pointer to a variable containing an error message which will be set by this*                       function to either:**                       OS_NO_ERR           if the memory partition has been created correctly.*                       OS_MEM_NO_FREE_BLKS if there are no more free memory blocks to allocate to caller*                       OS_MEM_INVALID_PMEM if you passed a NULL pointer for 'pmem'** Returns     : A pointer to a memory block if no error is detected*               A pointer to NULL if an error is detected**********************************************************************************************************/void  *OSMemGet (OS_MEM *pmem, INT8U *err){    void      *pblk;#if OS_CRITICAL_METHOD == 3                           /* Allocate storage for CPU status register      */    OS_CPU_SR  cpu_sr = 0;#endif#if OS_ARG_CHK_EN > 0    if (err == (INT8U *)0) {                          /* Validate 'err'                                */        return ((void *)0);    }    if (pmem == (OS_MEM *)0) {                        /* Must point to a valid memory partition        */        *err = OS_MEM_INVALID_PMEM;        return ((void *)0);    }#endif    OS_ENTER_CRITICAL();    if (pmem->OSMemNFree > 0) {                       /* See if there are any free memory blocks       */        pblk                = pmem->OSMemFreeList;    /* Yes, point to next free memory block          */        pmem->OSMemFreeList = *(void **)pblk;         /*      Adjust pointer to new free list          */        pmem->OSMemNFree--;                           /*      One less memory block in this partition  */        OS_EXIT_CRITICAL();        *err = OS_NO_ERR;                             /*      No error                                 */        return (pblk);                                /*      Return memory block to caller            */    }    OS_EXIT_CRITICAL();    *err = OS_MEM_NO_FREE_BLKS;                       /* No,  Notify caller of empty memory partition  */    return ((void *)0);                               /*      Return NULL pointer to caller            */}/*$PAGE*//***********************************************************************************************************                                   GET THE NAME OF A MEMORY PARTITION** Description: This function is used to obtain the name assigned to a memory partition.** Arguments  : pmem      is a pointer to the memory partition**              pname     is a pointer to an ASCII string that will receive the name of the memory partition.**              err       is a pointer to an error code that can contain one of the following values:**                        OS_NO_ERR                  if the name was copied to 'pname'*                        OS_MEM_INVALID_PMEM        if you passed a NULL pointer for 'pmem'*                        OS_ERR_PNAME_NULL          You passed a NULL pointer for 'pname'** Returns    : The length of the string or 0 if 'pmem' is a NULL pointer.**********************************************************************************************************/#if OS_MEM_NAME_SIZE > 1INT8U  OSMemNameGet (OS_MEM *pmem, INT8U *pname, INT8U *err){    INT8U      len;#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */    OS_CPU_SR  cpu_sr = 0;#endif    OS_ENTER_CRITICAL();#if OS_ARG_CHK_EN > 0    if (err == (INT8U *)0) {                     /* Validate 'err'                                     */        OS_EXIT_CRITICAL();        return (0);    }    if (pmem == (OS_MEM *)0) {                   /* Is 'pmem' a NULL pointer?                          */        OS_EXIT_CRITICAL();                      /* Yes                                                */        *err = OS_MEM_INVALID_PMEM;        return (0);    }    if (pname == (INT8U *)0) {                    /* Is 'pname' a NULL pointer?                         */        OS_EXIT_CRITICAL();                      /* Yes                                                */        *err = OS_ERR_PNAME_NULL;        return (0);    }#endif    len  = OS_StrCopy(pname, pmem->OSMemName);   /* Copy name from OS_MEM                              */    OS_EXIT_CRITICAL();    *err = OS_NO_ERR;    return (len);}#endif/*$PAGE*//***********************************************************************************************************                                 ASSIGN A NAME TO A MEMORY PARTITION** Description: This function assigns a name to a memory partition.** Arguments  : pmem      is a pointer to the memory partition**              pname     is a pointer to an ASCII string that contains the name of the memory partition.**              err       is a pointer to an error code that can contain one of the following values:**                        OS_NO_ERR                  if the name was copied to 'pname'*                        OS_MEM_INVALID_PMEM        if you passed a NULL pointer for 'pmem'*                        OS_ERR_PNAME_NULL          You passed a NULL pointer for 'pname'*                        OS_MEM_NAME_TOO_LONG       if the name doesn't fit in the storage area** Returns    : None**********************************************************************************************************/#if OS_MEM_NAME_SIZE > 1void  OSMemNameSet (OS_MEM *pmem, INT8U *pname, INT8U *err){    INT8U      len;#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */    OS_CPU_SR  cpu_sr = 0;#endif    OS_ENTER_CRITICAL();#if OS_ARG_CHK_EN > 0    if (err == (INT8U *)0) {                     /* Validate 'err'                                     */        OS_EXIT_CRITICAL();        return;    }    if (pmem == (OS_MEM *)0) {                   /* Is 'pmem' a NULL pointer?                          */        OS_EXIT_CRITICAL();                      /* Yes                                                */        *err = OS_MEM_INVALID_PMEM;        return;    }    if (pname == (INT8U *)0) {                    /* Is 'pname' a NULL pointer?                         */        OS_EXIT_CRITICAL();                      /* Yes                                                */        *err = OS_ERR_PNAME_NULL;        return;    }#endif    len = OS_StrLen(pname);                      /* Can we fit the string in the storage area?         */    if (len > (OS_MEM_NAME_SIZE - 1)) {          /* No                                                 */        OS_EXIT_CRITICAL();        *err = OS_MEM_NAME_TOO_LONG;        return;    }    (void)OS_StrCopy(pmem->OSMemName, pname);    /* Yes, copy name to the memory partition header      */    OS_EXIT_CRITICAL();    *err = OS_NO_ERR;}#endif/*$PAGE*//***********************************************************************************************************                                         RELEASE A MEMORY BLOCK** Description : Returns a memory block to a partition** Arguments   : pmem    is a pointer to the memory partition control block**               pblk    is a pointer to the memory block being released.** Returns     : OS_NO_ERR            if the memory block was inserted into the partition*               OS_MEM_FULL          if you are returning a memory block to an already FULL memory*                                    partition (You freed more blocks than you allocated!)*               OS_MEM_INVALID_PMEM  if you passed a NULL pointer for 'pmem'*               OS_MEM_INVALID_PBLK  if you passed a NULL pointer for the block to release.**********************************************************************************************************/INT8U  OSMemPut (OS_MEM *pmem, void *pblk){#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */    OS_CPU_SR  cpu_sr = 0;#endif#if OS_ARG_CHK_EN > 0    if (pmem == (OS_MEM *)0) {                   /* Must point to a valid memory partition             */        return (OS_MEM_INVALID_PMEM);    }    if (pblk == (void *)0) {                     /* Must release a valid block                         */        return (OS_MEM_INVALID_PBLK);    }#endif    OS_ENTER_CRITICAL();    if (pmem->OSMemNFree >= pmem->OSMemNBlks) {  /* Make sure all blocks not already returned          */        OS_EXIT_CRITICAL();        return (OS_MEM_FULL);    }    *(void **)pblk      = pmem->OSMemFreeList;   /* Insert released block into free block list         */    pmem->OSMemFreeList = pblk;    pmem->OSMemNFree++;                          /* One more memory block in this partition            */    OS_EXIT_CRITICAL();    return (OS_NO_ERR);                          /* Notify caller that memory block was released       */}/*$PAGE*//***********************************************************************************************************                                          QUERY MEMORY PARTITION** Description : This function is used to determine the number of free memory blocks and the number of*               used memory blocks from a memory partition.** Arguments   : pmem        is a pointer to the memory partition control block**               p_mem_data  is a pointer to a structure that will contain information about the memory*                           partition.** Returns     : OS_NO_ERR            If no errors were found.*               OS_MEM_INVALID_PMEM  if you passed a NULL pointer for 'pmem'*               OS_MEM_INVALID_PDATA if you passed a NULL pointer to the data recipient.**********************************************************************************************************/#if OS_MEM_QUERY_EN > 0INT8U  OSMemQuery (OS_MEM *pmem, OS_MEM_DATA *p_mem_data){#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */    OS_CPU_SR  cpu_sr = 0;#endif#if OS_ARG_CHK_EN > 0    if (pmem == (OS_MEM *)0) {                   /* Must point to a valid memory partition             */        return (OS_MEM_INVALID_PMEM);    }    if (p_mem_data == (OS_MEM_DATA *)0) {        /* Must release a valid storage area for the data     */        return (OS_MEM_INVALID_PDATA);    }#endif    OS_ENTER_CRITICAL();    p_mem_data->OSAddr     = pmem->OSMemAddr;    p_mem_data->OSFreeList = pmem->OSMemFreeList;    p_mem_data->OSBlkSize  = pmem->OSMemBlkSize;    p_mem_data->OSNBlks    = pmem->OSMemNBlks;    p_mem_data->OSNFree    = pmem->OSMemNFree;    OS_EXIT_CRITICAL();    p_mem_data->OSNUsed    = p_mem_data->OSNBlks - p_mem_data->OSNFree;    return (OS_NO_ERR);}#endif                                           /* OS_MEM_QUERY_EN                                    *//*$PAGE*//***********************************************************************************************************                                    INITIALIZE MEMORY PARTITION MANAGER** Description : This function is called by uC/OS-II to initialize the memory partition manager.  Your*               application MUST NOT call this function.** Arguments   : none** Returns     : none** Note(s)    : This function is INTERNAL to uC/OS-II and your application should not call it.**********************************************************************************************************/void  OS_MemInit (void){#if OS_MAX_MEM_PART == 1    OS_MemClr((INT8U *)&OSMemTbl[0], sizeof(OSMemTbl));   /* Clear the memory partition table          */    OSMemFreeList               = (OS_MEM *)&OSMemTbl[0]; /* Point to beginning of free list           */#if OS_MEM_NAME_SIZE > 1    OSMemFreeList->OSMemName[0] = '?';                    /* Unknown name                              */    OSMemFreeList->OSMemName[1] = OS_ASCII_NUL;#endif#endif#if OS_MAX_MEM_PART >= 2    OS_MEM  *pmem;    INT16U   i;    OS_MemClr((INT8U *)&OSMemTbl[0], sizeof(OSMemTbl));   /* Clear the memory partition table          */    pmem = &OSMemTbl[0];                                  /* Point to memory control block (MCB)       */    for (i = 0; i < (OS_MAX_MEM_PART - 1); i++) {         /* Init. list of free memory partitions      */        pmem->OSMemFreeList = (void *)&OSMemTbl[i+1];     /* Chain list of free partitions             */#if OS_MEM_NAME_SIZE > 1        pmem->OSMemName[0]  = '?';                        /* Unknown name                              */        pmem->OSMemName[1]  = OS_ASCII_NUL;#endif        pmem++;    }    pmem->OSMemFreeList = (void *)0;                      /* Initialize last node                      */#if OS_MEM_NAME_SIZE > 1    pmem->OSMemName[0]  = '?';                            /* Unknown name                              */    pmem->OSMemName[1]  = OS_ASCII_NUL;#endif    OSMemFreeList       = &OSMemTbl[0];                   /* Point to beginning of free list           */#endif}#endif