//Bit difference between active page state indicator value and
//transfer page state indicator value
#define OSAL_NV_ACTIVE_XFER_DIFF 0x00100000 //活动的pg头4字节标识
//active page state indicator value
#define OSAL_NV_ACTIVE_PAGE_STATE OSAL_NV_ACTIVE_XFER_DIFF
//transfer page state indicator value
#define OSAL_NV_XFER_PAGE_STATE (OSAL_NV_ACTIVE_PAGE_STATE ^ OSAL_NV_ACTIVE_XFER_DIFF)
最后一个，自己和自己异或下什么意思呢？
