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
欢迎大家拍砖!
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 */
}