eboot DownloadImage函数中为什么要调用OEMMapMemAddr（）？？

DownloadImage核心代码：

while (OEMReadData (sizeof (DWORD), (LPBYTE) &dwRecAddr)

			&& OEMReadData (sizeof (DWORD), (LPBYTE) &dwRecLen)

			&& OEMReadData (sizeof (DWORD), (LPBYTE) &dwRecChk)) {



			RETAILMSG(1, (_T("DownloadImage RecAddr: 0x%x\r\n"), dwRecAddr));

			RETAILMSG(1, (_T("DownloadImage RecLen:  0x%x\r\n"), dwRecLen));

			RETAILMSG(1, (_T("DownloadImage RecChk:  0x%x\r\n"), dwRecChk));



			// check for last record

			if (!dwRecAddr && !dwRecChk) {

				// if this is the kernel region, update launch address

				if (IsKernelRegion(dwImageStart, dwImageLength)) {

					*pdwImageStart  = dwImageStart;

					*pdwImageLength = dwImageLength;

					*pdwLaunchAddr  = dwRecLen;



        			RETAILMSG(1, (_T("dwImageStart : 0x%x\r\n"), dwImageStart));

        			RETAILMSG(1, (_T("dwImageLength: 0x%x\r\n"), dwImageLength));

        			RETAILMSG(1, (_T("LaunchAddr   : 0x%x\r\n"), dwRecLen));

				}



				// write to flash if it's flash image

				if (fIsFlash) {

					// finish the flash erase

					if (!OEMFinishEraseFlash ()) {

						HALT (BLERR_FLASH_ERASE);

						return FALSE;

					}

					// Before writing the image to flash, optionally check the image signature.

					if (g_pOEMCheckSignature)

					{

						if (!g_pOEMCheckSignature(dwImageStart, g_dwROMOffset, *pdwLaunchAddr, TRUE))

							HALT(BLERR_WHQL_SIGNATURE);

					}

				}



				// On to the next (possible) BIN file...

				break;

			}



			// map the record address (FLASH data is cached, for example)

			lpDest = OEMMapMemAddr (dwImageStart, dwRecAddr);



			// read data block

			if (!OEMReadData (dwRecLen, lpDest)) {

				EdbgOutputDebugString ("****** Data record %d corrupted, ABORT!!! ******\r\n", nPkgNum);

				HALT (BLERR_CORRUPTED_DATA);

				return FALSE;

			}



			if (!VerifyChecksum (dwRecLen, lpDest, dwRecChk)) {

				EdbgOutputDebugString ("****** Checksum failure on record %d, ABORT!!! ******\r\n", nPkgNum);

				HALT (BLERR_CHECKSUM);

				return FALSE;

			}

为什么要有lpDest = OEMMapMemAddr (dwImageStart, dwRecAddr);呢，我的理解这句if (!OEMReadData (dwRecLen, lpDest))的lpDest不应该是dwRecAddr吗？？我查baidu说是为了给flash映射Ram空间，DownloadImage不应该是把nk.bin内核解析成nk.nb0放到RAM然后就可以跳转运行了吗？

现在这样的话接收的数据不都在lpDest地址,而dwRecAddr地址出处会有数据吗？如果没有怎么可能执行内核代码？
不理解啊！！