ECC/NAND failures with EZSDK 5.05 w/ BCH8

Joel Keller

Hi,

I am attempting to upgrade EZSDK versions from 5.03 to 5.05. We have been using 5.03 for a long time, successfully, but I need to upgrade to EZSDK 5.05 for a variety of reasons - one of them being able to use BCH8 for u-boot & kernel.

I have finished porting over the few patches that we need to make to get the EZSDK to work with our board (this is not the EVM), but now I am having trouble with the NAND. I have flashed everything as BCH8, and in fact, I can boot all the way and linux is running, however I keep getting prints like these:

Read of newly-erased block at 0x00740000 failed: -74. Putting on bad_list

The system is "usable", but more and more of these pop up, and when I reboot to u-boot and run the "nand bad" command, I can see that more and more blocks are being marked bad.

This is the exact same unit that I have been using daily for many months, and it has never had even a single bad block before...now the list is many dozens.

Any ideas, places to start?

Thanks,

Joel

over 12 years ago

0 Joel Keller over 12 years ago

Expert 1305 points

Looking in to this further, I notice that the following note is written in the PSP 04.04.00.01 Release Notes:

UBIFS file system support has been enabled by default in the kernel. Since 8-bit BCH ECC scheme is using [2-57] bytes of the 64 byte OOB area in NAND, accommodating metadata for JFFS2 file system can not be supported with 8-bit ECC scheme. Hence, usage of UBIFS file system is recommended.

I am still using JFFS2. Seems like this is a likely cause of the errors I'm seeing. Can anyone confirm this? Is there anyway to continue to use JFFS2 with BCH8 ECC, or must I switch to UBIFS? Can anyone point me to the conflict in the OOB layout?

Thanks,

Joel

0 Vladimir-XID over 12 years ago in reply to Joel Keller

TI__Genius 11470 points

Joel,

Here is more info from the developers:

Is there really no support for BCH8 with JFFS2, only with UBIFS? In the release notes there is this warning (http://processors.wiki.ti.com/index.php/TI81XX_PSP_04.04.00.01_Release_Notes):

"UBIFS file system support has been enabled by default in the kernel. Since 8-bit BCH ECC scheme is using [2-57] bytes of the 64 byte OOB area in NAND, accommodating metadata for JFFS2 file system can not be supported with 8-bit ECC scheme. Hence, usage of UBIFS file system is recommended."

- JFFS2 cannot be used along with BCH8 ECC, only on 2K/64B NAND devices.
http://processors.wiki.ti.com/index.php/AM335x_JFFS2_Support_Guide#Reasons_for_disabling_JFFS2_support
http://processors.wiki.ti.com/index.php/TI81XX_PSP_UBOOT_User_Guide#BCH_Flash_OOB_Layout

- However JFFS2 can be supported with BCH8 ECC, on higher page-sized NAND

When using JFFS2 with BCH8 scheme:

- As a rule of thumb, you need to just check if following condition hold true.
   NAND OOBSize >= Bad-Block-Marker(2) + BCH8_ECC (14) * (page-size/512) + File-system metadata
   where:
       FileSystem metadata = 8 bytes for JFFS2
       FileSystem metadata = 0 bytes for UBIFS

   Thus for 2K/64B NAND device using JFFS2
   OOBSIZE = 64 is less than required area in OOB (2 + 14 * (2048/512) + 8 = 66)

Refer: http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/p/231420/815463.aspx#815463

http://processors.wiki.ti.com/index.php/Raw_NAND_ECC

http://processors.wiki.ti.com/index.php/Raw_NAND_ECC#Is_it_possible_to_use_any_ECC_algorithm_for_any_NAND.3F

Thank you.

Vladimir

0 Joel Keller over 12 years ago in reply to Vladimir-XID

Expert 1305 points

Thanks Vladimir,

I had found the answer to my question earlier, but your post was very helpful, thanks!. I now understand the JFFS2/OOB size relationship. I am indeed using a 2K/64B NAND. Turns out I have other ECC related problems, even when taking JFFS2 out of the equation.

Thanks for taking the time to reply.

-Joel

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ECC/NAND failures with EZSDK 5.05 w/ BCH8