Re: Serial EEPROM or Serial Flash?

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.arch.embedded
Subject	Re: Serial EEPROM or Serial Flash?
Date	2018-06-14 12:49 +0200
Organization	A noiseless patient Spider
Message-ID	<pfth8a$vpp$1@dont-email.me> (permalink)
References	<pftfgp$l3j$1@dont-email.me>

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On 14/06/18 12:20, pozz wrote:
> I need to save some data on a non-volatile memory. They are some
> parameters that the user could change infrequently, for example 10 times
> per day at a maximum.  In the range 100-2kB.
> 
> As usually occurs, the parameters that changes more frequently (10 times
> per day) are fewer than parameters that changes very rarely (10-100
> times in the device lifetime).
> 
> How to save those data? After discarding the internal MCU Flash (because
> of interrupts block during programming), I'm deciding if it's better a
> serial EEPROM or serial Flash.
> 
> First of all, I think SPI is better than I2C.  SPI seems much faster:
> 10-20MHz against 400kHz-1MHz.  At least for reading.  Erasing/writing
> time is identical between I2C and SPI.

Read time for this sort of thing is usually irrelevant.  Assuming you
are not badly constrained for ram, you read the NVM structure into
memory at startup and use it from there.  This makes it far easier to
use, and to handle things like duplicate structures in the NVM with
timestamps, checksums, etc.

> 
> EEPROM or Flash? I know EEPROM can be written one byte at a time without
> erasing an entire block, against Flash that needs a sector erase before
> writing even a single byte.

Roughly correct.  It is not an exact difference - there are devices
marketed as E²PROM which are written in, say, 32-byte blocks.  And there
are "flash" devices where you can write a single byte, and the device
handles reading the old page into a buffer, updating the byte, erasing
the page and re-writing.

> 
> The firmware would be simpler with EEPROMs, because I don't need to save
> the entire sector before erasing and restoring it during programming,
> when writing a single byte.  With EEPROMs I can write a byte.  Stop.
> 
> However I don't think this simple approach can be used in a real
> production.  Suppose I have 10 bytes to write.  What happens if the
> writing process is stopped at the middle, maybe after 5 bytes?  How to
> protect the system against those events?  I think one solution is to
> have at least two copies of data in the memory and switch to the other
> bank after all data is completely written, with an "atomic" write
> operation.

Multiple copies (at least 2) are key, along with timestamps or counters
and checksums.

> This means I need to copy&paste an entire block everytime, even for a
> single byte change.  And this is similar to Flash approach, where I
> *need* a sector erase before changing a single byte.

Yes.

Of course, it is possible to have multiple smaller blocks rather than
just one big one.  And you don't have to erase the old blocks until you
need to re-claim the space.

> 
> What about the time?  EEPROM write cycle is about 5ms for a 32-bytes
> page. For 128 bytes/4 pages, 20 ms.
> Flash sector erase time is 18 ms, plus 14us for each byte. The overall
> write cycle time is similar between EEPROM and Flash.
> 
> If the data are bigger, for example 1kB, the Flash technology wins.  The
> sector size in Flash memories are usually bigger than 1kB.  So I need to
> erase only one time (18m + 14u*1024=32ms).  In EEPROM I have 32 32-bytes
> pages, so 5m*32=160ms.  5 times more than Flash.
> 
> I'm not considering endurance.  EEPROMs are better (1000k write cycles)
> than Flash (100k write cycles), but I don't need so much write cycles in
> the entire device lifetime.
> 
> 
> After those considerations, I think I will choose a serial SPI Flash,
> maybe 512kbit.  The price is similar to serial EEPROM of only 64kbit.
> I see only one difficulty: how to write a good device driver to manage
> serial Flash: copy the content of a sector in another sector, making the
> changes on-the-fly, and switch from one sector to the other in one
> "atomic" operation.  Could you suggest some code to study?
> 
> I missed something other?  Please share your considerations.

Thread

Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-14 12:20 +0200
  Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-14 12:49 +0200
    Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 09:38 +0200
      Re: Serial EEPROM or Serial Flash? Jack <jack4747@gmail.com> - 2018-06-15 00:54 -0700
        Re: Serial EEPROM or Serial Flash? Reinhardt Behm <rbehm@hushmail.com> - 2018-06-15 16:26 +0800
          Re: Serial EEPROM or Serial Flash? Jack <jack4747@gmail.com> - 2018-06-15 01:31 -0700
          Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 10:50 +0200
            Re: Serial EEPROM or Serial Flash? Reinhardt Behm <rbehm@hushmail.com> - 2018-06-15 17:03 +0800
              Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 14:59 +0200
                Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-15 15:51 +0200
        Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 10:47 +0200
          Re: Serial EEPROM or Serial Flash? Jack <jack4747@gmail.com> - 2018-06-15 02:20 -0700
            Re: Serial EEPROM or Serial Flash? Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2018-06-15 13:41 +0200
            Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 15:01 +0200
      Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-15 11:25 +0200
        Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 15:10 +0200
          Re: Serial EEPROM or Serial Flash? Jack <jack4747@gmail.com> - 2018-06-15 06:51 -0700
          Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-15 16:21 +0200
            Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 17:20 +0200
              Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-15 13:11 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-15 22:54 +0200
                Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-15 18:25 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-16 08:26 +0200
                Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-16 09:20 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-16 19:38 +0200
                Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-16 16:41 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-16 23:05 +0200
              Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-17 18:41 +0200
            Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-16 20:12 +0200
              Re: Serial EEPROM or Serial Flash? David Brown <david.brown@hesbynett.no> - 2018-06-17 19:27 +0200
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-19 17:40 +0200
              Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-17 17:05 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-19 17:44 +0200
                Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-19 23:14 -0400
                Re: Serial EEPROM or Serial Flash? pozz <pozzugno@gmail.com> - 2018-06-20 11:03 +0200
                Re: Serial EEPROM or Serial Flash? Richard Damon <Richard@Damon-Family.org> - 2018-06-20 08:03 -0400
  Re: Serial EEPROM or Serial Flash? Michael Karas <mkaras@carousel-design.com> - 2018-06-23 09:43 -0700

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