uC/OS-II系统中的内存管理方法

转载请标明是引用于 http://blog.csdn.net/chenyujing1234

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代码下载： os_mem.c 、ucos_ii.h （http://www.rayfile.com/zh-cn/files/d1e9ff6e-e517-11e1-9a2b-0015c55db73d/）

一、引言

uC/OS-II的内存管理由自定义的分区（数组）来完成，根据需要进行初始化、创建、获得、释放；

注意它只是做管理，并没有提供真实使用的地址，使用的地址是通过OSMemCreate由外部提供的。

而了解这种机制，在我们平时的程序开发有多内存的应用场合，可是采用这种思想进行设备。

二、分析过程

1、内存的初始化

之前有准备好的数组OSMemTbl，然后根据要初始化的OS最大内存块数量OS_MAX_MEM_PART来初始化：

（1）如果只有一个，那么块指向第一个数组元素，指明它的OSMemName[0] = '?'；

（2）如果数量有2个或以上，那么就把相应数量的数组元素的OSMemname [0] = '?'；

总之，可以看出初始化只是把相应数量的数组元素的OSMenNames成员置为'?'。

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
}

2、创建内存（难点）

根据返回的OSMemFreeList指针查找下一个OSMemFreeList，看是否他为Free ，如果为Free直接返回；

如果不为Free那么根据传进来的内存开始地址、块的数量、每块的大小来初始化OSMemFreeList。

难点：

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);
}

3、内存的获得

从行参pmem中获得下一个Free的内存块，并让pmem的OSMemFreeList指针指向这块内存块。

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            */
}

4、内存的释放

与内存的获得OSMemGet相反，这里是把释放的内存插入到控件管理块中。

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       */
}