ABOUT KEIL AGSI setWatchOnMemory function

hi i use AGSI interface - SetWatchOnMemory((amECODE << 24) | startAddr, (amECODE << 24) | endAddr, callback, AGSIWRITE) to trigger excuting callback function when the memory between startAddr(0xf98000) and endAddr(0xff7fff) is writen. But only the memory in 0xfe0000~0xff7fff works(callback function is excuted), other memory(0xf98000~0xfdffff) doesn't work(when write these memory, callback function is not called).........why somebody help please