[ECOS] PROBLEM : JFFS2 on at91sam7x256ek

Jonathan Larmour jifl@eCosCentric.com
Thu Dec 11 10:29:00 GMT 2008

Peter Niebert wrote:
> On Wed, 10 Dec 2008 12:39:19 +0000, Jonathan Larmour <jifl@eCosCentric.com>
> wrote:
>>>	"arenasize 37032, freeblocks 1, totalallocated 528, totalfree 
>>>	36484, maxfree 36484
>>>	fsmount invalid
>>>	<FAIL>: mount() returned -1 Out of memory"
>>All the information is right there.
>>You've no hope of running JFFS2 on SAM7X BTW.
> Interesting to know, how much memory would you need?

If you managed to fit it into the 64K RAM of a SAM7X you might be able to 
create a small empty filesystem, or with a small number of small files 
written with a small number of fragments. But you're very likely to run 
out of heap as the number of nodes increase (every time you write()), some 
of which persist in RAM.  All of them are in RAM while the file is open of 
course. And then remember there's also memory overhead for the fileio 
layer too. After _that_ you'd want to think of the memory available to run 
a useful application. Most likely you'd have a very unstable system where 
you rapidly found writes would start returning ENOMEM errors.

Maybe you could make it read-only which would bound the memory use, but in 
that case you may as well use ROMFS.

So, IMO no hope.

> And how about FAT?

It's caching is more deterministic and bounded, via CDL. You could 
probably do something with that with 64K. Of course FAT is famously 
deficient with respect to data integrity.

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