Messages in this thread | | | Subject | Re: FFS2 and MTDs (flash) | Date | Mon, 05 Jul 1999 20:06:38 +0100 | From | David Woodhouse <> |
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jgg@ualberta.ca said: > Yes, there is lots of benifit to being able to mount a FFS filesystem > over a loop device or on a RAM disk or something else. There is also > lots of benifit to being able to create the FFS off the flash and then > write the whole thing in one go. For my purposes that is a crucial > feature. Also since the MTD's are presented as block devices you can > mount other FS's like romfs in read-only mode.
OK - that sounds reasonable.
jgg@ualberta.ca said: > Things will also run a bit faster if the buffer cache is used to hang > onto some often used filesystem meta data in main memory.
Think of CFI-compliant flash mapped into the host's address space. Why cache it in RAM when you can just point a page table at the original?
> XIP is not directly possible with FFS2 as it places no constraints on > alignment (like romfs).
So what they say on their web site about XIP is all crap? Of course, I suppose that shouldn't surprise me :)
Is it possible to run Linux on FFS2 without some kind on UMSDOS-like translation layer? Are we going to want to write our own version which is POSIX-compliant?
> You're welcome to my code so far if you are interested, I have > support for an Octagon 5066, a V-Max 301 and untested support for > something called a MixCom card.
Yes please - that'd be useful.
> BTW, I thought Disk on a chip used an ATA interface, and wasn't really > a MTD?
No, it maps into the host's memory map between 0xD0000 and 0xE0000 and has a custom ASIC to interface to the flash. The old versions behaved very similarly to EMS, paging in different blocks of flash - but the new version is very different, and very strange.
It's CompactFlash that uses an ATA interface, either PCMCIA-ATA or raw IDE. So you don't even need PCMCIA support to use it, I believe.
---- ---- ---- David Woodhouse David.Woodhouse@mvhi.com Office: (+44) 1223 810302 Project Leader, Process Information Systems Mobile: (+44) 976 658355 Axiom (Cambridge) Ltd., Swaffham Bulbeck, Cambridge, CB5 0NA, UK. finger dwmw2@ferret.lmh.ox.ac.uk for PGP key.
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