Re: [Yaffs] yaffs handle chunk error calling

On Tuesday 20 September 2011 14:47:08 Xiaoguang Chen wrote:
> Hi, Yaffs friends
> I have one question about yaffs_handleChunkError function calling code
> logic. In yaffs_ReadChunkWithTagsFromNAND:
>

>          if (tags &&
>             tags->eccResult > YAFFS_ECC_RESULT_NO_ERROR) {

>

>                   yaffs_BlockInfo *bi;
>                    bi = yaffs_GetBlockInfo(dev,
> chunkInNAND/dev->param.nChunksPerBlock); yaffs_HandleChunkError(dev, bi);
>          }

>
> Why use "tags->eccResult > YAFFS_ECC_RESULT_NO_ERROR " instead of
> "tags->eccResult > YAFFS_ECC_RESULT_FIXED" ?
>
> If the flash has some one bit errors and these errors are corrected,
> Tags->eccResult will be set to YAFFS_ECC_RESULT_FIXED. in this condition,
> there should be no ecc problem. Why need to call yaffs_HandleChunkError ?

We do this because we want to handle errors on the block before they start
corrupting data.
>
> The problem is : if call yaffs_HandleChunkError, bi->chunkErrorStrikes++
> will be executed. After chunkErrorStrikes > 3, the block will be retired.
> It will be marked as bad. But the block is not really bad. We can still use
> it since it only has 4 times of fixed ECC error happened.

If you have 1-bit correcting ECC then the above policy handles things well
because single bit errors indicate that a block might have started going bad
and we want to retire it before the block starts corrupting data.

If you have multi-bit correcting data then it makes sense to modify what the
driver reports.

eg if you have 4 bit correcting then something like this makes sense:
For 0,1 or 2 errors report NO ERROR.
For 3 or 4 errors report FIXED.


-- Charles