2440 bootloader中，MBR是什么东西？该如何解决

// lqm: 1G08:dwStartSector = 7 * 64 (boot:7个block)
HANDLE BP_OpenPartition(DWORD dwStartSector, DWORD dwNumSectors, DWORD dwPartType, BOOL fActive, DWORD dwCreationFlags)
{
        DWORD dwPartIndex;
        BOOL fExists;

        ASSERT (g_pbMBRSector);
        
        if (!IsValidMBR()) // 这里的目的是什么???
        {
            DWORD dwFlags = 0;

            if (dwCreationFlags == PART_OPEN_EXISTING) 
            {
                RETAILMSG(1, (TEXT("OpenPartition: Invalid MBR.  Cannot open existing partition 0x%x.\r\n"), dwPartType));
                return INVALID_HANDLE_VALUE;
            }
            
            RETAILMSG(1, (TEXT("OpenPartition: Invalid MBR.  Formatting flash.\r\n")));
            if (g_FlashInfo.flashType == NOR) 
            {
                dwFlags |= FORMAT_SKIP_BLOCK_CHECK;
            }
            BP_LowLevelFormat (0, g_FlashInfo.dwNumBlocks, dwFlags);
            dwPartIndex = 0;
            fExists = FALSE;
        }
        else 
        {
            fExists = GetPartitionTableIndex(dwPartType, fActive, &dwPartIndex);        
        }

        RETAILMSG(1, (TEXT("OpenPartition: Partition Exists=0x%x for part 0x%x.\r\n"), fExists, dwPartType));
        if (fExists) {

            // Partition was found.  
            if (dwCreationFlags == PART_CREATE_NEW)
                return INVALID_HANDLE_VALUE;
            
            if (g_partStateTable[dwPartIndex].pPartEntry == NULL) {
                // Open partition.  If this is the boot section partition, then file pointer starts after MBR
                g_partStateTable[dwPartIndex].pPartEntry = (PPARTENTRY)(g_pbMBRSector + PARTTABLE_OFFSET + sizeof(PARTENTRY)*dwPartIndex);
                g_partStateTable[dwPartIndex].dwDataPointer = 0;
            }            
            return (HANDLE)&g_partStateTable[dwPartIndex];            
        }
        else {

            // If there are already 4 partitions, or creation flag specified OPEN_EXISTING, fail.
            if ((dwPartIndex == NUM_PARTS) || (dwCreationFlags == PART_OPEN_EXISTING))
                return INVALID_HANDLE_VALUE;

            // Create new partition
            return CreatePartition (dwStartSector, dwNumSectors, dwPartType, fActive, dwPartIndex);
        }

        return INVALID_HANDLE_VALUE;
        
}

static BOOL IsValidMBR() 
{
    // Check to see if the MBR is valid

    // MBR block is always located at logical sector 0
    g_dwMBRSectorNum = GetMBRSectorNum();        

    RETAILMSG (1, (TEXT("IsValidMBR: MBR sector = 0x%x\r\n"), g_dwMBRSectorNum));
   
    if ((g_dwMBRSectorNum == INVALID_ADDR) || !FMD_ReadSector (g_dwMBRSectorNum, g_pbMBRSector, NULL, 1)) 
    {
        return FALSE;  
    }
    // lqm added for test.10-04-12
    RETAILMSG (1, (TEXT("g_pbMBRSector[0] = 0x%x\r\n"), g_pbMBRSector[0]));
    RETAILMSG (1, (TEXT("g_pbMBRSector[1] = 0x%x\r\n"), g_pbMBRSector[1]));
    RETAILMSG (1, (TEXT("g_pbMBRSector[2] = 0x%x\r\n"), g_pbMBRSector[2]));
    RETAILMSG (1, (TEXT("g_pbMBRSector[SECTOR_SIZE-2] = 0x%x\r\n"), g_pbMBRSector[SECTOR_SIZE-2]));
    RETAILMSG (1, (TEXT("g_pbMBRSector[SECTOR_SIZE-1] = 0x%x\r\n"), g_pbMBRSector[SECTOR_SIZE-1]));
    // end added.
    return ((g_pbMBRSector[0] == 0xE9) &&
         (g_pbMBRSector[1] == 0xfd) &&
         (g_pbMBRSector[2] == 0xff) &&
         (g_pbMBRSector[SECTOR_SIZE-2] == 0x55) &&
         (g_pbMBRSector[SECTOR_SIZE-1] == 0xAA));
}