eboot中NBL1的 nand.c中的 CorrectECC8Data函数有什么作用？解决方法

eboot中NBL1的 nand.c中的 CorrectECC8Data函数有什么作用？
最近在看wince5.0 的bootloader的block0image即nboot的源代码。。在NBL1的nand.c文件中有个CorrectECC8Data(unsigned char *pEncodingBaseAddr)。。这个函数如果检测到了不可矫正的位错误就会返回1。。。。返回1时。。NAND_Read函数就返回false。。。然后NBL1读取NBL2就失败了。。但是我把NAND_Read函数那边retrun flase;屏蔽掉后系统能读到NBL2。。。也能正常启动。。。我用的flash是三星的K9GAG08U0M...（4k+128byte）页大小的。。
现在我的问题是：
1、不是说存放block0image的flash的第一块是保证是可用块的。。那还需要ecc校验吗？
2、那我把那个ecc校验的代码按代码注释的地方屏蔽掉后。。系统可以正常启动。。那这个校验有什么作用呢？
望大家给个指点。。小弟感激不尽。。。

C/C++ code



//NBL1中读取Nbl2的代码
//K9GAG08U0M为mlc的flash

    NAND_Init();

    Read_DeviceID(0, &ucDID, &ucHID);  
    Uart_SendString("Device ID : 0x");
    Uart_SendBYTE(ucDID, 1);
    Uart_SendString("Hidden ID : 0x");
    Uart_SendBYTE(ucHID, 1);


    if ((ucDID == 0xd5 && ucHID == 0x14) || (ucDID == 0xd5 && ucHID == 0x94) || (ucDID == 0xd7 && ucHID == 0x55)  // for MLC
        || (ucDID == 0xd3 && ucHID == 0x10) || (ucDID == 0xd7 && ucHID == 0xd5))  // for SLC
    {
        b4KPage = TRUE;
        uNumOfLoadPage = LOAD_PAGE_SIZE/2;
    }

    // Turn the LEDs off.
//    Led_Display(LED_OFF);
//
    pBuf = (unsigned char *)LOAD_ADDRESS_PHYSICAL;
//    while(1);
    // MLC
    // Page 0, 1 : Steploader
    // Page 2 ~ 5 : empty page
    // Page 6 ~ PAGES_PER_BLOCK-3 : effective page
    // read pages with 0, 1 and 6 to PAGES_PER_BLOCK-3
#ifdef SUPPORTSLC
    nPage = LOAD_IMAGE_PAGE_OFFSET;
#endif
#ifdef SUPPORTMLC
    nPage = 10;
#endif

    for (nCnt = 0; nCnt < uNumOfLoadPage; nCnt++)
    {
        if (nPage >= (NAND_PAGE_PER_BLOCK-2) || (NAND_Read(0, nPage, pBuf, b4KPage) == FALSE))
        {
            // Uncorrectable ECC Error
            Uart_SendString("ECC Error @ Page 0x");
            Uart_SendBYTE(nPage, 1);
            //Led_Display(0x9);
            while(1); //NAND_Read 返回false 后就直接死循环
        }

        nPage++;

        if (b4KPage == TRUE)
            pBuf += NAND_BYTE_PER_PAGE*2;
        else
            pBuf += NAND_BYTE_PER_PAGE;
    }

C/C++ code




//NAND_Read函数和 CorrectECC8Data函数的实现。。。
//
BOOL NAND_Read(DWORD dwBank, DWORD dwPage, unsigned char *pBuf, BOOL b4KPage)
{
    DWORD SpareDataDummy;
    DWORD dwOffset;
    DWORD dwCnt;
    DWORD dwSpareAddress = 2048 + 1;    //include Bad block

    unsigned char uSctCnt;
    BOOL bRet = TRUE;

    if (b4KPage == TRUE) uSctCnt = 8;
    else uSctCnt = 4;

    rNFCONF = ( rNFCONF&~(0x3<<23) ) |(2<<30)|(1<<23)|(0x7<<12)|(0x7<<8)|(0x7<<4);
    rNFCONT = ( rNFCONT&~(0x1<<18) ) |(0<<18)|(0<<11)|(0<<10)|(0<<9)|(1<<6)|(1<<0); // Init NFCONT    
    rNFSTAT |= ((1<<6)|(1<<5)|(1<<4));

    NAND_Reset(dwBank);
    
    NF_MECC_Lock(); // Main ECC Lock
    NF_CE_L(dwBank);
    rNFSTAT |= (1<<4); // RnB Clear


    NF_CMD(CMD_READ);
    NF_SET_ADDR(dwPage, 0x00);
    NF_CMD(CMD_READ_CONFIRM);
    NF_DETECT_RB();
    rNFSTAT |= (1<<4); // RnB Clear

    //READ Spare ECC Data
    for(dwCnt = 0; dwCnt < uSctCnt; dwCnt++) {
        NF_MECC_Lock(); // Main ECC Lock
        rNFSTAT |= (1<<4); // RnB Clear

        if(!dwCnt) {
            NF_CMD(CMD_READ);
            NF_SET_ADDR(dwPage, 0);
            NF_CMD(CMD_READ_CONFIRM);

            NF_DETECT_RB();
            rNFSTAT |= (1<<4); // RnB Clear            
        }
        else
        {
            dwOffset = dwCnt * 512;
            NF_CMD(CMD_RANDOM_DATA_OUTPUT);
            NF_ADDR(dwOffset&0xFF);
            NF_ADDR((dwOffset>>8)&0xFF);
            NF_CMD(CMD_RANDOM_DATA_OUTPUT_CONFIRM);
        }

        NF_MECC_UnLock();     // Main ECC Unlock
        NF_MECC_Reset();     // Initialize ECC
 
        //read 512byte
        _Read_512Byte(pBuf + 512*dwCnt);

                if (b4KPage == TRUE)
                        dwOffset = 4096 + (dwCnt * 13);
                else
                        dwOffset = 2048 + (dwCnt * 13);

        NF_CMD(CMD_RANDOM_DATA_OUTPUT);
        NF_ADDR(dwOffset&0xFF);
        NF_ADDR((dwOffset>>8)&0xFF);
        NF_CMD(CMD_RANDOM_DATA_OUTPUT_CONFIRM);

        //read Spare ECC Data        
        SpareDataDummy = NF_DATA_R4();
        SpareDataDummy = NF_DATA_R4();
        SpareDataDummy = NF_DATA_R4();
        SpareDataDummy = NF_DATA_R();

        NF_MECC_Lock(); // Main ECC Lock

        while(!(rNFSTAT&(1<<6)));     // Check decoding done 
        rNFSTAT = rNFSTAT | (1<<6);   // Decoding done Clear

        while( rNF8ECCERR0 & (unsigned int)(1<<31) ) ; // 8bit ECC Decoding Busy Check.

        if(CorrectECC8Data((pBuf + 512*dwCnt))) {
        //    return FALSE; //这边注释掉后NBL1就可以正常读取NBL2。。且NBL2能正常执行。。读取eboot 并启动系统。。。
//这边注释掉后CorrectECC8Data函数对于不能纠正的bit错误就没有返回了。。
//如果数据有错没纠正。。那系统为什么还能启动？

        }        
    }

    NF_CE_H(dwBank);
    
    return TRUE;
}




int CorrectECC8Data(unsigned char *pEncodingBaseAddr)
{    
    unsigned int i,uErrorByte[9];
    unsigned char uErrorBit[9];
    unsigned int uErrorType;
    
    
    uErrorType = (rNF8ECCERR0>>25)&0xf;// Searching Error Type //How many Error bits does exist?    
    uErrorByte[1] = rNF8ECCERR0&0x3ff;// Searching Error Byte //Where is the error byte?
    uErrorByte[2] = (rNF8ECCERR0>>15)&0x3ff;    
    uErrorByte[3] = (rNF8ECCERR1)&0x3ff;
    uErrorByte[4] = (rNF8ECCERR1>>11)&0x3ff;    
    uErrorByte[5] = (rNF8ECCERR1>>22)&0x3ff;    
    uErrorByte[6] = (rNF8ECCERR2)&0x3ff;
    uErrorByte[7] = (rNF8ECCERR2>>11)&0x3ff;
    uErrorByte[8] = (rNF8ECCERR2>>22)&0x3ff;
    
    uErrorBit[1] = rNFMLC8BITPT0&0xff;// Searching Error Bit //Where is the error bit?
    uErrorBit[2] = (rNFMLC8BITPT0>>8)&0xff;
    uErrorBit[3] = (rNFMLC8BITPT0>>16)&0xff;
    uErrorBit[4] = (rNFMLC8BITPT0>>24)&0xff;    
    uErrorBit[5] = rNFMLC8BITPT1&0xff;
    uErrorBit[6] = (rNFMLC8BITPT1>>8)&0xff;
    uErrorBit[7] = (rNFMLC8BITPT1>>16)&0xff;
    uErrorBit[8] = (rNFMLC8BITPT1>>24)&0xff;
    
    if(uErrorType == 0x0) {
        return 0;
    }

    if(uErrorType == 0x9) {
        return 1;
    }
    for(i=1;i<=uErrorType ;i++)    
    {
        if(uErrorByte[i] < 512)    
            pEncodingBaseAddr[uErrorByte[i]]^=uErrorBit[i];
        else
        {;    }            
    }
    return 0;
    
}

eboot中NBL1的 nand.c中的 CorrectECC8Data函数有什么作用？解决方法

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