UC/OS-II的内存管理OSMemCreate()分析

OS_MEM *OSMemCreate (void *addr, INT32U nblks, INT32U blksize, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPUstatusregister */
OS_CPU_SR cpu_sr;
#endif
OS_MEM *pmem;
INT8U *pblk;
void **plink;
INT32U i;

/*检测参数的正确性*/
#if OS_ARG_CHK_EN > 0
if (addr == (void *)0) { /* Must pass a valid address for the memory part. */
*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);
}
#endif

OS_ENTER_CRITICAL();
/*得到空闲的内存控制块*/
pmem = OSMemFreeList; /* Get next free memory partition */
/*更新内存控制块链表*/
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);
}
/*
将一个分区的各个内存小块链接起来，
形成一个链表
*/
plink = (void **)addr; /* Create linked list of free memoryblocks */
/*得到一个固定的*/
pblk = (INT8U *)addr + blksize;
for (i = 0; i < (nblks - 1); i++) {
/*在当前的地址处保存下一个内存块的地址*/
*plink = (void *)pblk;
/*将指针指向下一个内存块*/
plink = (void **)pblk;
/*得到第三个内存块的地址*/
pblk = pblk + blksize;
}
/*
将最后一个内存块的下一个地址设置为NULL；
*/
*plink = (void *)0; /* Last memoryblockpoints to NULL */
/*得到内存分区的起始地址*/
pmem->OSMemAddr = addr; /* Store start address ofmemorypartition */
/*
将内存块的链表头指向当前地址
通过链表能够快速的找到下一个内存块的地址
只需要对链表取地址，
然后将指针指向该地址就能实现快速的切换
*/
pmem->OSMemFreeList = addr; /* Initialize pointer to pool of free blocks */
/*空闲的内存块*/
pmem->OSMemNFree = nblks; /* Store number of free blocks in MCB */
/*内存的总块数*/
pmem->OSMemNBlks = nblks;
/*内存块的大小*/
pmem->OSMemBlkSize = blksize; /* Store block size of eachmemoryblocks */
*err = OS_NO_ERR;
return (pmem);
}

plink = (void **)addr; /* Create linked list of free memory blocks */
pblk = (INT8U *)addr + blksize;
for (i = 0; i < (nblks - 1); i++) {
*plink = (void *)pblk;
plink = (void **)pblk;
pblk = pblk + blksize;
}
*plink = (void *)0; /* Lastmemoryblockpoints to NULL */