Linux/AM3352: How to enable 4-bit ECC for NAND

Is this for Linux?

Steve K.

yes, this is for Linux

Steve,

Thanks for the follow-up. That seems strange to have a board with 4-bit ECC NAND but we program it for 8-bit and it works. Do you know if the ECC functionality has been tested with this setup? What specific board are you referring to? I check and the AM335x EVM has a schematic place-holder for a NAND but it's marked DNI and there is not part number. The AM335x Starter Kit has no NAND, and the BBB has eMMC managed NAND.

Regardless, it sounds like we will not be able to use 4-bit ECC NAND since our boot ROM doesn't support it.

Looks like the following wiki confirms your statement that 4-bit ECC is not supported in our boot rom.

Thanks,

-Brad

Brad, really the only restriction is the spare area formatting that the ROM code expects during boot (this is outlined in the Initialzation chapter of the TRM), which supports BCH8 or 16 as Steve mentioned.  On the AM335x GP EVM, there is a NAND on the GP daughtercard (there is a spot for another NAND on the main board which is not populated).  The GP daughtercard NAND has the requirement for 4-bit ECC at a minimum, but to satisfy the ROM requirement, the spare area should be formatted with ECC BCH8

Regards,

James

Thanks James.

If I can live with out ECC during initial ROM boot but want to enable from within u-boot to be used during loading the kernel and filesystem, how do I go about enabling it?

Thanks

You have to use ECC to boot, and the boot ROM only understands BCH8 and BCH16.

In the u-boot source, look at include/configs/am335x_evm.h. That is where the NAND information is set. When you build u-boot, both MLO and u-boot will use the ECC algorithm selected. When you use u-boot to flash the NAND, it will be flashed with the ECC selected in the .h file. This NAND should work on AM335x.

Steve K.

Thanks Steve.

So I've been reading the TRM in great detail plus other reading and I beleive I have a grasp on this, at least from the HW capabilities and how our ROM code handles things. I agree that for our particular device, we should be okay using BCH 8-bit ECC.

Our part is the S34ML01G200TF100. From it's datasheet...

• x8, 1Gb: 2048+64 page size so 64 bytes spare area per page. That's enough spare area to hold the ECC code for all four 512byte sectors in each page
• ONFI 1.0 compliant so it will provide the ONFI parameters page to get page size, block size, etc.

We would just need to make sure SYSBOOT[9] is pulled low if we want to have the ROM code use ECC

That leaves the question of how to enable ECC in software once MLO has been loaded by the ROM. I looked at the am335x_evm.h file you referred to, thanks for sharing that. I don't know what all the settings mean but to me they look reasonable as-is for our NAND device.

Here's a dumb question though. In the am335x_evm.h file, looks like all the NAND settings depend on the preprocessor symbol CONFIG_NAND to be set. I didn't see it being set in the ti_am335x_common.h file. I'm not that familiar with customizing u-boot, I usually just build it from the top level SDK makefile. So where would I define CONFIG_NAND? Should I set it as a -d define on the make command line? Should I just define it in a header file? Just looking for the place where something like this is normally defined so I'm not doing anything stupid.

Thanks