uboot的bug？

xiao_in

u-boot-1.1.4/commond/cmd_nand.c

1080行左右（我的程序改过，行数可能不同），nand_write_page函数里

/* Calculate and write the ECC if we have enough data */
if ((col < nand->eccsize) && (last >= nand->eccsize))
{
        nand_calculate_ecc (&nand->data_buf[0], &(ecc_code[0]));
        for (i = 0; i < 3; i++)
        {
                nand->data_buf[(nand->oobblock + oob_config.ecc_pos)] = ecc_code;
        }
        if (oob_config.eccvalid_pos != -1)
        {
                nand->data_buf[nand->oobblock + oob_config.eccvalid_pos] = 0xf0;
        }
}

/* Calculate and write the second ECC if we have enough data */
if ((nand->oobblock == 512) && (last == nand->oobblock))
{
        nand_calculate_ecc (&nand->data_buf[256], &(ecc_code[3]));
        for (i = 3; i < 6; i++)
        {
                nand->data_buf[(nand->oobblock + oob_config.ecc_pos)] = ecc_code;
        }
        if (oob_config.eccvalid_pos != -1)
        {
                nand->data_buf[nand->oobblock + oob_config.eccvalid_pos] &= 0x0f;
        }
}
在这里进行了两次ecc，而且ecc_code也写进了data_buf，512-527中

再后面
for (i = 0; i < col; i++)
        nand->data_buf = 0xff;

/* Postpad for partial page programming !!! oob is already padded */
for (i = last; i < nand->oobblock; i++)
        nand->data_buf = 0xff;

为什么又把data_buf的某些部分置成0xff，前面按不是0xff校验了，置成0xff不就错了吗？这里是怎么回事？（不懂ecc算法）
有人调通nand write命令没？