open question on flash speed/app blocking

Christopher Fowler cfowler at
Tue Jan 15 13:44:03 EST 2002

I've noticed that when I write to a file on my DOC2000 that they bus 
does not block until the bufffers are flushd.  My flashing program 
issues a sync() before unmounting the flash.  I even write a 21kb 
config to a raw partition.  That can take a while too.    I'm not sure 
if there is a way around this.  On the DOC2000 you need to use at least 
a block size of 4096.  Since the M-SYS driver reads and writes in those 
block sizes.  Maybe some other people here can talk about this subject.


> Hi all,
> We're making an app that periodically writes a persistance file to 
flash.  I 
> haven't actually gotten a flash file system area working yet on my 
board, so 
> i can't test this yet for speed.   I know that the results will vary 
with the 
> hardware, the filesystem used, and a handful of other factors.  I'm 
> that a write to the flash will be blocking - that is, nothing else 
will be 
> allowed to happen on the bus while that function is being performed.
> For a file the size of 32bytes, 1kByte, and 32kBtyes, what kind of 
> delay might one expect from linux writing to flash for each of those 
> sizes?  What would be an optimum flash filesystem to use for 
something like 
> this?  (if there is one)
> cheers,
> cam
> ps. i'm using linux 2.4.6-rmk1-rayl1 and 2.4.16-rmk2.  I could use 
the latest 
> kernel, too, i just haven't gotten around to it.  For development 
> i'm using a cirrus CDB89712 development board, which has the cs89712 
> processor and some Intel 28f320B3 flash on it.
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