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

[Andrew Dyer]

On Mon, Aug 17, 2009 at 12:58 PM, Jake Peavy<djstunks at 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.