small erase block size with EBS

small erase block size with EBS

[kevinwu]

I have a NAND flash with a small erase block(16KiB)
When I use sumtool, I find that the summary image size is much larger
than the original one if I use option --eraseblock=0x4000.
But When I use option --eraseblock=0x20000, The summary image is a bit
larger than the original one.
EBS fits for large erase block as far as I know. 
That is to say, I can not use EBS if the NAND erase block is small. What
a pitty!
What about CS?
Is there any way to use EBS on a small erase block size NAND?
If there is not, I have to modify JFFS2 souce code in order to make a
128KiB erase block size image to work on a 16KiB erase block size NAND
flash.

-- 
Best Regards

Kevin Wu

System Software Engineer, E28.com


Office: 86-21-32224888-207

Re: small erase block size with EBS

[Ferenc Havasi]

Hi,

> I have a NAND flash with a small erase block(16KiB)
> When I use sumtool, I find that the summary image size is much larger
> than the original one if I use option --eraseblock=0x4000.
> But When I use option --eraseblock=0x20000, The summary image is a bit
> larger than the original one.
> EBS fits for large erase block as far as I know. 
> That is to say, I can not use EBS if the NAND erase block is small. What
> a pitty!
 > Is there any way to use EBS on a small erase block size NAND?

EBS should work on your system but if the erase block size is small it 
may be not too usefull. Generally if you use bigger erase block size the 
speedup will be greater and the "used place penalty" will be smaller.

So I suggest to test it: measure the rete of speedup and the difference 
in image size on your system, and you can decide it is OK for you or not.

> What about CS?

CS doesn't depend on erase block size as EBS does, so you may try it. 
The code of CS is more then one mouth old, so you should use it with 
earlier mtd snapshot. If you can wait a little we will update it at the 
first week of december.

Ferenc

Re: small erase block size with EBS

[kevinwu]

Hi Ferenc,
I successfully mounted a 128KiB erase block size summary image on a
16KiB erase block size NAND. The mounting speed is very high. It takes
only about 0.5 second mounting on a 32MiB partition with 90% disk
full.(My cpu is ARM926 running at 201 MHz) It seems OK. The performance
is good. I modified JFFS2 source code a little.
I changed souce code in function jffs2_do_fill_super()
from:
c->sector_size = c->mtd->size;
to:
c->sector_size = 0x00020000; //erase block size of image you generated. 

It does work if the jffs2 partition has no bad block.
If there is a bad block, it will get error imformation. But I will fix
this bug soon. I know what happend. 

在 2005-11-22二的 14:53 +0100，Ferenc Havasi写道：
> Hi,
> 
> > I have a NAND flash with a small erase block(16KiB)
> > When I use sumtool, I find that the summary image size is much larger
> > than the original one if I use option --eraseblock=0x4000.
> > But When I use option --eraseblock=0x20000, The summary image is a bit
> > larger than the original one.
> > EBS fits for large erase block as far as I know. 
> > That is to say, I can not use EBS if the NAND erase block is small. What
> > a pitty!
>  > Is there any way to use EBS on a small erase block size NAND?
> 
> EBS should work on your system but if the erase block size is small it 
> may be not too usefull. Generally if you use bigger erase block size the 
> speedup will be greater and the "used place penalty" will be smaller.
> 
> So I suggest to test it: measure the rete of speedup and the difference 
> in image size on your system, and you can decide it is OK for you or not.
> 
> > What about CS?
> 
> CS doesn't depend on erase block size as EBS does, so you may try it. 
> The code of CS is more then one mouth old, so you should use it with 
> earlier mtd snapshot. If you can wait a little we will update it at the 
> first week of december.
It seems a better choise. I will try it.

Thanks for your information.
-- 
Best Regards

Kevin Wu

System Software Engineer, E28.com


Office: 86-21-23060088-352