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[DM814x笔记]BCH Flash OOB Layout  

2013-02-24 11:28:11|  分类: TI_8148 |  标签: |举报 |字号 订阅

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For any ECC scheme we need to add some extra data while writing so as to detect and correct (if possible) the errors introduced by the NAND part. In case of BCH scheme some bytes are needed to store the ECC related info. The section of NAND memory where addition info like ECC data is stored is referred to as Out Of Band or OOB section.

The first 2 bytes are used for Bad block marker-0xFFFF => Good block

The next ‘N’ bytes is used for BCH bytes

N = B * <Number of 512-byte sectors in a page>

B = 8 bytes per 512 byte sector in BCH4

B = 14 bytes per 512 byte sector in BCH8

B = 26 bytes per 512 byte sector in BCH16

So for a 2k page-size NAND flash with 64-byte OOB size, we will use BCH8. This will consume 2 + (14*4) = 58 bytes out of 64 bytes available.

 

ECC Schemes and their context of usage

ECC type

Usage

S/W ECC

Not used

H/W ECC–Hamming Code

Should use this scheme while flashing any image/binary which will be used by Linux. This is also used for the U-Boot ENV variables.

H/W ECC-BCH8

Only while flashing U-Boot from U-Boot already running out of OCMC RAM1. After flashing revert back to hamming code H/W ECC

To select ECC algorithm for NAND:

TI8148_EVM# nandecc [sw | hw <hw_type>]

Usage:

sw - Set software ECC for NAND

hw <hw_type> - Set hardware ECC for NAND

<hw_type> - 0 for Hamming code

          1 for bch4

          2 for bch8

          3 for bch16

Currently we support only Software, Hamming Code and BCH8. We do not support BCH4 and BCH16

Reference

DM814x AM387x PSP U-Boot.pdf

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