Re: Flash retention in uC at higher temps, experience?

Frank Buss wrote:
> Joerg wrote:
> 
>> One could add some code so it re-flashes itself once in a while, that's

>> another option here. However, the device cannot lose power during that 
>> brief period or it'll be really toast. So that would require large 
>> enough electrolytics and some pre-regulator voltage monitoring. The 
>> latter would require a relayout, bigger ECO and all that. Not a VP of 
>> Engineering's favorite path, usually.
> 
> If the flash is big enough, you could copy the program to an unused
memory
> area and back again the next cycle. Then the only critial moment is
writing
> the switchover. But should be no problem, if you can monitor the supply
> voltage and if you can guarantee, that it remains over the flash limit
for
> the time needed to write the switchover bytes.
> 

That's one of the methods I am thinking about. It would require a uC 
with at least twice the flash size but heck, that would be pretty cheap 
insurance. The switchover could be handled by a flag that will not get 
asserted before the whole transfer is complete. Only afterwards would 
the flag for the "old" flash area be disasserted.

The flag is the problem. Unfortunately uC manufacturers have not put 
that much thought into the reset routine. It just jumps to a fixed 
address and when the data there is corrupt the application is toast.


> What do you think of MRAM for critial applications? It's a bit
expensive,
> but they claim data retention of minimum 20 years and unlimited number
of
> writes. It is even used in a satellite:
> 
> http://www.eetimes.com/showArticle.jhtml?articleID=206900226
>
http://www.freescale.com/files/microcontrollers/doc/data_sheet/MR2A16A.pdf
> 

We already have another kind of memory in one application because of 
flash corruption. However, then the question arises: Why have flash in 
the first place?

-- 
Regards, Joerg

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