DDR Memory Failure

[hideoushog]

Although I have not seen any problem caused by this I am worried that inexplicable errors may occur in the future if I accept my recently purchased Plug Compter. On starting up with memory test enabled I get the following error. Is it something I should worry about?

No. of BootROM routine retries: 524288
NAND: Nand ECC error


Running diagnostics ...

        DDR2 data bus test                               PASSED

        DDR2 address bus test                            PASSED

        DDR2 device test                                 PASSED

        Device: 0, Size: 512 MB, Page Size: 2 KB, Block Size: 128 KB
        NAND detection test                              PASSED

        Bad Block: 03480000
        Bad Block: 034a0000
        Bad Block: 0b4a0000
        Bad Block: 1bb00000
        Bad Block: 1f9c0000
        Bad Block: 1f9e0000
        NAND bad-block detection test                    PASSED

        Speed: 100 Mbps, Duplex: Full, Link: up
        GbE link detect test                             PASSED

        RTC test                                         PASSED

Diag completed

[pingtoo]

I see no where in the diagnostic show DDR error, it fact they all seems to passed. whereas the error indicate you have some bad blocks in your on board NAND. This is to be expected. All manufacture have some small percentage defect it is consider acceptable. You can lookup NAND in wikipedia I think there is a explanation of this.

[hideoushog]

Thanks for the advice. I found out the following, and that boot loaders need to read a bad block table and avoid using those blocks.


  Bad Blocks

NAND memory apparently gets shipped with blocks that are already bad. The vendor just marks those blocks as bad, thus resulting in higher yield and lower per-unit cost.

The flash contains four kinds of blocks (16kBytes):

    * Factory-Default bad blocks
          o Samsung marks the 6th OOB byte as non 0xFF in the first and/or second page in blocks that are bad
    * Worn-out bad blocks
    * Good blocks
    * The first block.
          o This block is guaranteed to not require error correction up to 1000 writes. This is needed as initial boot code can't do ECC.

We are also guaranteed that a minimum of 4026 blocks (out of the total 4096) are good. This means up to 70 blocks (1.3MBytes) can be dead, resulting in a total guaranteed amount of working NAND storage of 65961984 bytes.