UC/OS-II的內(nèi)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;

/*檢測參數(shù)的正確性*/
#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();
/*得到空閑的內(nèi)存控制塊*/
pmem = OSMemFreeList; /* Get next free memory partition */
/*更新內(nèi)存控制塊鏈表*/
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);
}
/*
將一個分區(qū)的各個內(nèi)存小塊鏈接起來，
形成一個鏈表
*/
plink = (void **)addr; /* Create linked list of free memoryblocks */
/*得到一個固定的*/
pblk = (INT8U *)addr + blksize;
for (i = 0; i < (nblks - 1); i++) {
/*在當(dāng)前的地址處保存下一個內(nèi)存塊的地址*/
*plink = (void *)pblk;
/*將指針指向下一個內(nèi)存塊*/
plink = (void **)pblk;
/*得到第三個內(nèi)存塊的地址*/
pblk = pblk + blksize;
}
/*
將最后一個內(nèi)存塊的下一個地址設(shè)置為NULL；
*/
*plink = (void *)0; /* Last memoryblockpoints to NULL */
/*得到內(nèi)存分區(qū)的起始地址*/
pmem->OSMemAddr = addr; /* Store start address ofmemorypartition */
/*
將內(nèi)存塊的鏈表頭指向當(dāng)前地址
通過鏈表能夠快速的找到下一個內(nèi)存塊的地址
只需要對鏈表取地址，
然后將指針指向該地址就能實現(xiàn)快速的切換
*/
pmem->OSMemFreeList = addr; /* Initialize pointer to pool of free blocks */
/*空閑的內(nèi)存塊*/
pmem->OSMemNFree = nblks; /* Store number of free blocks in MCB */
/*內(nèi)存的總塊數(shù)*/
pmem->OSMemNBlks = nblks;
/*內(nèi)存塊的大小*/
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 */