Re: Nvram write modes and problems

In comp.arch.embedded,
Robert Adsett <sub2@xxxxxxxxxxxxxxxxxxxxx> wrote:
In article <euh2nc$4r6$01$1@xxxxxxxxxxxxxxxxx>, Hans-Bernhard Bröker
says...
Robert Adsett wrote:

It's non-volatile, random access and rewriteable.

... but it's not really "memory".

Sure it is. The size of the bus shouldn't have any bearing on the
issue. Note Philips has sold IIC devices for some time that it refers
to as RAM.

I'm not too happy with calling EEPROM random access. Sure you can read
any location you want, but to get any performance out of them you'll
want to read them sequentially. And to get something written, you need
to send a few commands first, wait for previuos writes to finish and
only write a single page at the time.


I2C EEPROMs and other serially
attached devices like them are non-volatile *storage*.

I can see the distinction you are making. I sympathise but I'm not sure
I agree. If you make a distinction based on ease of write then flash
becomes non-volatile storage rather than memory. Not a distinction I'd
be happy with.

To me, the distinction is in the technology: EEPROM, FLASH, FRAM, RAM and
if you add battery backup to RAM you get NVRAM.

FLASH is only random access when reading, writing is very different.
When running code from a FLASH, I'm happy with refering to it as ROM.
When I need it to store data, it's FLASH again or maybe NV storage.

They're really
too different from actual RAM to be called NVRAM.

I don't agree. NVRAM is simply an intermediate storage form that sits
on the spectrum between between volatile RAM and mass storage. The
distinctions are rather grey but NVRAM includes EE and FRAM as well as
BBRAM as far as I'm concerned.

That would be my definition of non-volatile storage, with NVRAM being
one of the possible flavours.

But where is your boudary between NVRAM(storage) and mass storage? How
do you call an SD FLASH 1GB card? There is not a whole lot of difference
between updating a sector oriented FLASH device and a harddisk, why
would one be intermediate storage and the other be mass storage?

OTOH, I'm not going to insist you agree with my definition only realize
others don't necessarily share your narrower definition.

OK, we agree to disagree then.

Certainly the OP should have at least mentioned the technology of NVRAM
being used but I don't believe he should have been corrected on his
terminology.

The OP experienced memory corruption, so the first thing that you would
like to know is the type of memory. Calling it NVRAM confused me enough
to not know for sure what he was talking about, and I'm sure I was not
the only one. So I stand by my correction.

The boundaries between memory types is rather fuzzy and shows every sign
of getting fuzzier in the future.

I find them mostly clear enough for now, but that may change. ;-)
For me, only FRAM is a bit fuzzy. I don't have a real problem with calling
the parallel version NVRAM.

--
Stef (remove caps, dashes and .invalid from e-mail address to reply by mail)

.

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