[U-Boot] OT-ish: NOR flash write speed degradation?

[U-Boot] OT-ish: NOR flash write speed degradation?

[Jake Peavy]

Hi all,

As I feel this list is a good resource for embedded design minds, please
forgive this elementary question.

As NOR flash ages, does write speed degrade?  Or do writes take place at
roughly the same rate over time until the part reaches the write limit
(100k-1000k writes)?  Any pointers in the right direction would be great.

Thanks for your time.

-- 
-jp

Even though he was an enemy of mine, I had to admit that what he had
accomplished was a brilliant piece of strategy. First, he punched me, then
he kicked me, then he punched me again.

deepthoughtsbyjackhandey.com

[U-Boot] OT-ish: NOR flash write speed degradation?

[Andrew Dyer]

On Mon, Aug 17, 2009 at 12:58 PM, Jake Peavy<djstunks@gmail.com> wrote:
> Hi all,
>
> As I feel this list is a good resource for embedded design minds, please
> forgive this elementary question.
>
> As NOR flash ages, does write speed degrade? ?Or do writes take place at
> roughly the same rate over time until the part reaches the write limit
> (100k-1000k writes)? ?Any pointers in the right direction would be great.
>
> Thanks for your time.

I believe it's the erase time that grows - it takes longer to tunnel
the charge off of the floating gate as it ages (which is a separate
mechanism from the write).

With some of the original flash parts (Intel 28F008 & friends, IIRC),
you had to time the erase operations yourself, and you could get some
extended lifetime from the parts by just allowing more time for the
erase to complete.  These days that's all handled by embedded state
machines in the parts.  Also the old parts didn't have an internal
charge pump, you had to feed them +12V for programming and erase ops.

[U-Boot] OT-ish: NOR flash write speed degradation?

[Wolfgang Denk]

Dear Jake Peavy,

In message <c5221b990908171058s5e3b5f76j1aa6c6e0abc269b9@mail.gmail.com> you wrote:
>
> As I feel this list is a good resource for embedded design minds, please
> forgive this elementary question.

You are welcome.

> As NOR flash ages, does write speed degrade?  Or do writes take place at

Yes, it does. Both erase and write times grow, sometimes significantly
compared to "virgin" values when the flash was new.

> roughly the same rate over time until the part reaches the write limit
> (100k-1000k writes)?  Any pointers in the right direction would be great.

We've seen doubling of erase and write times much earlier, say after
some 10...100 erase/write cycles.

Best regards,

Wolfgang Denk

-- 
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