RE: nandtest error

Tee Zhen Cong
2015-04-30T02:51:08Z

Hi Jeff,
You have a point there seeing that we do not know what is the nandtest is
doing and whether ECC is in place during the test.
I am changing my test method. I will attach a ubifs onto the NAND flash.
Then I will try and do format-write-read a big file (> 1GByte). I am sure
ubifs has the ECC correction mechanism in place, and I believe we are able
to test the NAND. If the file is corrupted after writing into NAND, then I
guess something is wrong. Am I correct to say that?

Regards,
zc

-----Original Message-----
From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of
Jeff Lauruhn (jlauruhn)
Sent: Thursday, 30 April, 2015 10:06 AM
To: Tee Zhen Cong; 'Han Xu'
Cc: linux-mtd@lists.infradead.org
Subject: RE: nandtest error

Hello zc;
The MT29F16G08CBACA is a 70 series part (25nm), 24 bit/1080 bytes of ECC vs
MT29F32G08CBADA 80 series (20nm) 40 bits/1117 bytes of ECC, these are very
different parts. ECC of 40 bits/1117 bytes will correct 320 bits per page
and 81920 bits per block so if I read this correctly 31 of 81920 bits have
flipped in this case. My point here is that with ECC correction this device
will be good past the 3000 P/E cycles guaranteed, but if you look at any raw
NAND without ECC correction you will very likely see some flipped bits.
This is normal NAND behavior, especially on smaller nodes.

Jeff Lauruhn
NAND Application Engineer
Embedded Business Unit
Micron Technology, Inc

-----Original Message-----
From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of
Tee Zhen Cong
Sent: Wednesday, April 29, 2015 6:29 PM
To: Jeff Lauruhn (jlauruhn); 'Han Xu'
Cc: linux-mtd@lists.infradead.org
Subject: RE: nandtest error

Hi Jeff,
The flipped bits is found in the first 2Mbytes (1st block) of the NAND. It
stops at the first block where errors are detected. I am not so sure what is
happening in the nandtest application. It seems like a standard linux test
tool for nand where many ppl use. So I use it for my test as well.
As far as I see, it erase, write then read back the NAND block by block, and
see if the read back bytes are the same with the written bytes.
In my opinion, the flipped bits is not normal. I got another board with a
useable 16GBit NAND (MT29F16G08CBACA). Using the nandtest application, it
returns successful without any flipped bit. Same kernel, same software. Only
different NAND.

Regards,
zc

-----Original Message-----
From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of
Jeff Lauruhn (jlauruhn)
Sent: Thursday, 30 April, 2015 5:12 AM
To: Han Xu; Tee Zhen Cong
Cc: linux-mtd@lists.infradead.org
Subject: RE: nandtest error

When you read the data back are you reading the raw data? Some amount of
bit flipping is normal NAND Flash behavior. ECC correction is required on
all contemporary NAND to some degree to correct bit flips. This Micron
device is designed to return a "FAIL" status only when the number of bad
bits in any page exceeds 40bits/1117 bytes.

I need to understand what nandtest is actually doing. If I read this right,
if found 32 flipped bits in a 32 gigabit device. That's actually very good.

Jeff Lauruhn
NAND Application Engineer
Embedded Business Unit
Micron Technology, Inc

-----Original Message-----
From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of
Han Xu