ucosII OSMemCreate()函数的解析 .(双指针构成链表)

转载自

http://blog.csdn.net/langaopeng/article/details/7386526

 

ucosII OSMemCreate()函数的解析

OS_MEM  *OSMemCreate (void *addr, INT32U nblks, INT32U blksize, INT8U *perr)
{
    plink = (void **)addr;                           
    pblk  = (INT8U *)((INT32U)addr + blksize);
    for (i = 0; i < (nblks - 1); i++) {
       *plink = (void *)pblk;                       
        plink = (void **)pblk;                       
        pblk  = (INT8U *)((INT32U)pblk + blksize);  
    }
    *plink              = (void *)0;                 
    pmem->OSMemAddr     = addr;                     
    pmem->OSMemFreeList = addr;                     
    pmem->OSMemNFree    = nblks;                     
    pmem->OSMemNBlks    = nblks;
    pmem->OSMemBlkSize  = blksize;                  
    *perr               = OS_ERR_NONE;
    return (pmem);
}

当nblk = 2,也就是说准备申请两块动态内存块时。

当执行 plink = (void **)addr;时,因为addr之前是一维指针，没有指向地址，所以需要
强转成二维指针，使用addr能指向地址，此时把addr赋给plink。但*plink还不知指向哪里。

当执行pblk  = (INT8U *)((INT32U)addr + blksize);后，即把第二块的头指针赋给
pblk。

当执行*plink = (void *)pblk; 后，即把第二块头指针赋给*plink，即addr内装的指针。

即可知当传递addr时，addr是指向的是第一块内存的头指针，强转时，addr内装的
指针是指向第二块头指针。

 

 

 

在原作者基础上，我把os_mem.c文件贴出来:

/*
*********************************************************************************************************
*                                                uC/OS-II
*                                          The Real-Time Kernel
*                                            MEMORY MANAGEMENT
*
*                              (c) Copyright 1992-2007, Micrium, Weston, FL
*                                           All Rights Reserved
*
* File    : OS_MEM.C
* By      : Jean J. Labrosse
* Version : V2.86
*
* LICENSING TERMS:
* ---------------
*   uC/OS-II is provided in source form for FREE evaluation, for educational use or for peaceful research.  
* If you plan on using  uC/OS-II  in a commercial product you need to contact Micri祄 to properly license 
* its use in your product. We provide ALL the source code for your convenience and to help you experience 
* uC/OS-II.   The fact that the  source is provided does  NOT  mean that you can use it without  paying a 
* licensing fee.
*********************************************************************************************************
*/

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

#if (OS_MEM_EN > 0) && (OS_MAX_MEM_PART > 0)
/*
*********************************************************************************************************
*                                        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.
*
*               perr     is a pointer to a variable containing an error message which will be set by
*                        this function to either:
*
*                        OS_ERR_NONE              if the memory partition has been created correctly.
*                        OS_ERR_MEM_INVALID_ADDR  if you are specifying an invalid address for the memory
*                                                 storage of the partition or, the block does not align
*                                                 on a pointer boundary
*                        OS_ERR_MEM_INVALID_PART  no free partitions available
*                        OS_ERR_MEM_INVALID_BLKS  user specified an invalid number of blocks (must be >= 2)
*                        OS_ERR_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 *perr)
{
    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 (perr == (INT8U *)0) {                         /* Validate 'perr'                               */
        return ((OS_MEM *)0);
    }
    if (addr == (void *)0) {                          /* Must pass a valid address for the memory part.*/
        *perr = OS_ERR_MEM_INVALID_ADDR;
        return ((OS_MEM *)0);
    }
    if (((INT32U)addr & (sizeof(void *) - 1)) != 0){  /* Must be pointer size aligned                  */
        *perr = OS_ERR_MEM_INVALID_ADDR;
        return ((OS_MEM *)0);
    }
    if (nblks < 2) {                                  /* Must have at least 2 blocks per partition     */
        *perr = OS_ERR_MEM_INVALID_BLKS;
        return ((OS_MEM *)0);
    }
    if (blksize < sizeof(void *)) {                   /* Must contain space for at least a pointer     */
        *perr = OS_ERR_MEM_INVALID_SIZE;
        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             */
        *perr = OS_ERR_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        */
    *perr               = OS_ERR_NONE;
    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
*
*               perr    is a pointer to a variable containing an error message which will be set by this
*                       function to either:
*
*                       OS_ERR_NONE             if the memory partition has been created correctly.
*                       OS_ERR_MEM_NO_FREE_BLKS if there are no more free memory blocks to allocate to caller
*                       OS_ERR_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 *perr)
{
    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 (perr == (INT8U *)0) {                         /* Validate 'perr'                               */
        return ((void *)0);
    }
    if (pmem == (OS_MEM *)0) {                        /* Must point to a valid memory partition        */
        *perr = OS_ERR_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();
        *perr = OS_ERR_NONE;                          /*      No error                                 */
        return (pblk);                                /*      Return memory block to caller            */
    }
    OS_EXIT_CRITICAL();
    *perr = OS_ERR_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.
*
*              perr      is a pointer to an error code that can contain one of the following values:
*
*                        OS_ERR_NONE                if the name was copied to 'pname'
*                        OS_ERR_MEM_INVALID_PMEM    if you passed a NULL pointer for 'pmem'
*                        OS_ERR_PNAME_NULL          You passed a NULL pointer for 'pname'
*                        OS_ERR_NAME_GET_ISR        You called this function from an ISR
*
* Returns    : The length of the string or 0 if 'pmem' is a NULL pointer.
*********************************************************************************************************
*/

#if OS_MEM_NAME_SIZE > 1
INT8U  OSMemNameGet (OS_MEM *pmem, INT8U *pname, INT8U *perr)
{
    INT8U      len;
#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 (perr == (INT8U *)0) {                    /* Validate 'perr'                                    */
        return (0);
    }
    if (pmem == (OS_MEM *)0) {                   /* Is 'pmem' a NULL pointer?                          */
        *perr = OS_ERR_MEM_INVALID_PMEM;
        return (0);
    }
    if (pname == (INT8U *)0) {                   /* Is 'pname' a NULL pointer?                         */
        *perr = OS_ERR_PNAME_NULL;
        return (0);
    }
#endif
    if (OSIntNesting > 0) {                      /* See if trying to call from an ISR                  */
        *perr = OS_ERR_NAME_GET_ISR;
        return (0);
    }
    OS_ENTER_CRITICAL();
    len   = OS_StrCopy(pname, pmem->OSMemName);  /* Copy name from OS_MEM                              */
    OS_EXIT_CRITICAL();
    *perr = OS_ERR_NONE;
    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.
*
*              perr      is a pointer to an error code that can contain one of the following values:
*
*                        OS_ERR_NONE                if the name was copied to 'pname'
*                        OS_ERR_MEM_INVALID_PMEM    if you passed a NULL pointer for 'pmem'
*                        OS_ERR_PNAME_NULL          You passed a NULL pointer for 'pname'
*                        OS_ERR_MEM_NAME_TOO_LONG   if the name doesn't fit in the storage area
*                        OS_ERR_NAME_SET_ISR        if you called this function from an ISR
*
* Returns    : None
*********************************************************************************************************
*/

#if OS_MEM_NAME_SIZE > 1
void  OSMemNameSet (OS_MEM *pmem, INT8U *pname, INT8U *perr)
{
    INT8U      len;
#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 (perr == (INT8U *)0) {                    /* Validate 'perr'                                    */
        return;
    }
    if (pmem == (OS_MEM *)0) {                   /* Is 'pmem' a NULL pointer?                          */
        *perr = OS_ERR_MEM_INVALID_PMEM;
        return;
    }
    if (pname == (INT8U *)0) {                   /* Is 'pname' a NULL pointer?                         */
        *perr = OS_ERR_PNAME_NULL;
        return;
    }
#endif
    if (OSIntNesting > 0) {                      /* See if trying to call from an ISR                  */
        *perr = OS_ERR_NAME_SET_ISR;
        return;
    }
    OS_ENTER_CRITICAL();
    len = OS_StrLen(pname);                      /* Can we fit the string in the storage area?         */
    if (len > (OS_MEM_NAME_SIZE - 1)) {          /* No                                                 */
        OS_EXIT_CRITICAL();
        *perr = OS_ERR_MEM_NAME_TOO_LONG;
        return;
    }
    (void)OS_StrCopy(pmem->OSMemName, pname);    /* Yes, copy name to the memory partition header      */
    OS_EXIT_CRITICAL();
    *perr = OS_ERR_NONE;
}
#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_ERR_NONE              if the memory block was inserted into the partition
*               OS_ERR_MEM_FULL          if you are returning a memory block to an already FULL memory
*                                        partition (You freed more blocks than you allocated!)
*               OS_ERR_MEM_INVALID_PMEM  if you passed a NULL pointer for 'pmem'
*               OS_ERR_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_ERR_MEM_INVALID_PMEM);
    }
    if (pblk == (void *)0) {                     /* Must release a valid block                         */
        return (OS_ERR_MEM_INVALID_PBLK);
    }
#endif
    OS_ENTER_CRITICAL();
    if (pmem->OSMemNFree >= pmem->OSMemNBlks) {  /* Make sure all blocks not already returned          */
        OS_EXIT_CRITICAL();
        return (OS_ERR_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_ERR_NONE);                        /* 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_ERR_NONE               if no errors were found.
*               OS_ERR_MEM_INVALID_PMEM   if you passed a NULL pointer for 'pmem'
*               OS_ERR_MEM_INVALID_PDATA  if you passed a NULL pointer to the data recipient.
*********************************************************************************************************
*/

#if OS_MEM_QUERY_EN > 0
INT8U  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_ERR_MEM_INVALID_PMEM);
    }
    if (p_mem_data == (OS_MEM_DATA *)0) {        /* Must release a valid storage area for the data     */
        return (OS_ERR_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_ERR_NONE);
}
#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                                                    /* OS_MEM_EN                                 */