high density serial flash

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Hi folks,

Can anyone recommend high density serial flash parts for embedded system
code storage?  I'm looking for at least 8Mbit, preferably 16 or even 32.

Nexflash aren't shipping yet, and 16mbit isn't expected until mid next
year.  Similarly SST is only up to 2 or 4mbit right now.  I saw a
mention on EE times of Taiwanese companies Mycomp and TMC, but could
find no info on their serial flash devices.

For this application, we just need to store code/data that will be
copied into RAM at boot time.  Is there another technology that might be
suitable in the densities I'm looking for?

Low pin count is the main priority.

I've also looked at NAND flash, which has a fairly low pin count, but am
a bit put off by the complexity of implementing controller hardware and
software that will only be in use at bootup.

Any suggestions?

Thanks,

John


Re: high density serial flash
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Take a look at ATMEL's Dataflash - currently up to 128Mbit (and going
further apparently) They also offer Dataflash Cards (which are in the
standard MMC format). They have a nice upgrade path from 1 Mbit up to the
maximum - in both BGA and TSSOP packages.

We have used Dataflash to store an embbedded Linux distribution, and have
even mapped the dataflash to the file system.

They use a SPI interface.






Re: high density serial flash
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Ah yes, that's the ticket!  That's exactly what we'll be storing,
uClinux kernel and filesystem images - in this case the kernel is
running on a soft-core processor inside a Xilinx FPGA.

Thanks for that Simon,

Regards,

John


Re: high density serial flash
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sorry - forgot to add the URL : http://www.atmel.com/products/DataFlash/



Re: high density serial flash
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Just curious - what exactly is the complexity here? It's simple to
develop a very easy proprietary filesystem running on NAND flash,
particularly when your app is "write once, read many". Basically, just
store your data linearly, and skip blocks that are marked bad.

Re: high density serial flash
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Yes fair point - SPI-based serial flash would be nice because there are
already SPI cores that I can use (processor is FPGA-based) - know any
refs of app notes discussing the h/w interface between Nand flash and a
microprocessor?  Since it's just a start-up operation, I wonder if I
could get away with just bitbanging over a GPIO-style interface...  must
look more closely at the data sheets.

Thanks,

John


Re: high density serial flash
Hi John,

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You most certainly can do it with GPIOs; that's the way I did it first time
round. I can give you some sample C code for the block-level access, if you
like.  But it's simple enough to deduce how to do it from the chip
datasheet, nothing complicated there. The complexities lie in error
correction and the fact that a FAT filesystem normally lives at the next
level up.





Re: high density serial flash
Hi Lewin,

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I would be very interested to see some sample code for this.  As you
say, it can be inferred from the data sheets but at this early
evaluation stage it would be very helpful to me.

As for file systems, it's not such a big deal for me... I could
potentially partition the flash, use a boot block in a simple "raw" mode
to boot, then once linux boots use the MTD Nand flash drivers with a
proper filesys over the top.

Cheers,

John


Re: high density serial flash
On Wed, 17 Sep 2003 14:43:58 +1000, John Williams

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     ST has serial flash products in this range.


Re: high density serial flash
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The largest part listed on their website is 8Mbit - I'd need at least 2
of them, plus level translators since I'm interfacing with 2.5V IO.

Also does anyone have experience with the Atmel dataflash, I've had at
least one opinion that they are unreliable and have a rather low
write-cycle count (< 1000).  Seems a shame, since they have the high
densities that I'm looking for.  Any comments?

Thanks,

John


Re: high density serial flash
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My understanding is it is basically unlimited.  From memory you just need to
a block erase before any of the pages in that block reach 10k cycles.  This
is from memory, atmel has an app note on it somewhere.

Ralph



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