Re: [Yaffs] How does YAFFS handle Memory deterioration?

Hi
Thanks for answering!
Interesting with the year 2038 problem but i do not think i will have this
problem because i will not use any os or possible some real simple os on a
STM32F4 microcontroller. But it’s worth checking.

Ok it sounds good that there are no FAT tables or any other file management
data that will deteriorate. I was worried about that.

Have been looking on how to port YAFFS to my STM32 microcontroller and I
find it quite hard to figure out which file I should put the write and read
drivers for my nand flash. Does anyone know any example code were YAFFS have
been ported to a microcontroller without any os? (I am mostly working with
hardware so I am kind of slow in coding)

Regarding how much ram that I need. I will have YAFFS on a 128 Mbyte flash
memory and my picture files will be around 800 Kbyte each. Will it be enough
for me to only rely on the internal 196 Kbytes SRAM in the STM32F4
microcontroller for reading and writing these pictures?

I have also been thinking of using nor flash and was thinking of simply
storing raw data without any file system. But how prone to broken blocks are
nor flash? I will only rewrite the pictures around 30 times on the flash
memory. Can I trust nor flash if I only write it 30 times or will I get
problems with bad blocks? Is it necessary to have error correction code and
bad block management when using nor flash?

//Jimmie

-----Original Message-----
From: Charles Manning
Sent: Wednesday, July 24, 2013 11:44 PM
To: yaffs@lists.aleph1.co.uk
Cc: Jimmie Hansson
Subject: Re: [Yaffs] How does YAFFS handle Memory deterioration?

On Monday 03 June 2013 06:07:59 Jimmie Hansson wrote:
> Hi
>
> I am considering using YAFFS for storing pictures on a NAND flash in a
> device that need to be able to function for 30 years. The pictures on the
> NAND flash will get written to the flash when it gets manufactured and
> then
> the device will rewrite the pictures every year so that the pictures don’t
> get corrupt from memory deterioration. The data retention on a normal
> NAND
> flash is about 10 years.
>
> Is YAFFS a file system that will be suitable for this kind of long life
> application?
>
> How does YAFFS handle Memory deterioration?
>
> Will it be enough for me to rewrite a file every year for it to not get
> corrupt of memory deterioration or are there any other crucial data in the
> file system that will get corrupt over time?

Hello Jimmie

I think that would work pretty well.

If you are going to make a product like that then I would be careful to test
any implications of http://en.wikipedia.org/wiki/Year_2038_problem

Yaffs does not really have other data to get corrupted. There is no FAT
table
or such. That actually makes it a very good candidate for the type of usage
you are considering.

There is a very small chance that old stuff in the log (ie. discarded data)
could come alive again through "bit rot". It would make some sense to do
some
background garbage collection to clear this up. This is already wired into
Linux but can easily be hooked up with other OSs.


-- CHarles