[U-Boot-Users] Can I write to flash using mw command

[Ben Warren]

Bilahari,

On Wed, 2006-10-11 at 22:17 +0000, bilahari wrote:

>    But one thing that doesnt work with my code and also 
> with u-boot is that if I want to write two different 
> values to the same flash locationconsecutively 
> ( for example when I try to write 0x12 to flash address
> 0xff000000 and then write 0x34 to same flash address, 
> u-boot gives me a message "flash not erased". 
> My driver makes the program simply loop forever in a status
> register polling loop, I guess).
> 
> Is it something natural with flash programming ?. 
> Should I always erase the whole sector before I re-program 
> a location ? (doesnt sound like a good approach to me), 
> is it not possible to write consecutively as with 
> the conventional memory?

Flash can't be accessed like the RAM you're thinking of.  You can only
change a bit state from 1 to 0 (That's why after erasing a sector you'll
see that the contents are all 'ffffffff').  For all intents and
purposes, once you write to a location in flash, it's 'read-only' until
you erase the whole sector again.  Also, keep in mind that flash devices
have a limited number of erase cycles before performance becomes
unreliable.  A common value is 100000 cycles, although there are devices
with more and less than this number.  In general, use Flash to store
information that will change infrequently.

regards,
Ben