EEPROM guarantees after power loss during a write

Arlet <usenet+5@c-scape.nl> writes:

> On Feb 8, 11:58 am, John Devereux <jdREM...@THISdevereux.me.uk> wrote:
>
>> I would still love to know, for sure, that a write to part of a page
>> does not involve an internal erasure of the entire page. Without
>> knowing this each version stamp needs a page of its own as far as I
>> can see. The act of writing the version number must be guaranteed not
>> to upset the data it refers to, if it gets interrupted.
>>
>> I think I will have to try and test this.
>
> To test the system, you could make a simple test jig that switches the
> power to your board. Use another controller to switch the power in
> random intervals. The random interval timing should match the
> discharge rate of the power supply capacitors such that the board
> suffers a lot of brown out conditions. Add an extra R/C filter if
> necessary.
>
> On the device you're testing, set up some special firmware that
> continously writes updates to the EEPROM. Instead of real data, write
> a verifiable test pattern, and have the software check it regularly.
> If it finds corrupted data in a 'valid' block, trigger an alarm.
>
> Then leave the test setup in a corner of the lab, 24/7.

That sounds like a good idea to test a finished routine.

But to get the initial information needed to write it, I am thinking
of this:

 - Hack the electronics so the EEPROM can be powered from an output
   pin
 - hack my eeprom_write routine so that a timer can interrupt power to
   the EEPROM and hold the I2C pins low (so the eeprom is definitely
   unpowered).

That allows the timer to interrupt programming using a precise time
delay that I can sweep though a range of values. For each value I can

 - print the eeprom page contents (to a serial port)
 - reprogram the entire page with a test pattern
 - start the timer and the page programming test
   (different pattern, only alters part of page)

I should be able to see any partial erasures, partial programming, and
also any erasure of bytes on the same page outside of the program
area.

Perhaps I would printout extra regions like address 0 and parts of
adjacent pages.

This does not simulate a real system since there is no "brownout"
state. So I still need something like your setup as a final
verification.

-- 

John Devereux