[U-Boot] incremental environment updating

[Wolfgang Denk]

Dear Mike,

In message <200904130834.35359.vapier at gentoo.org> you wrote:
>
> > Since flash can change 1s to 0s, but cannot change them back, you could
> > redefine the env storage to be
> >    <next><crc><env><NUL>[undefined]
> > (note the added <next> at the start).  By definition, the valid env's
> > <next> =3D=3D 0xFFFFFFFF.  To write a new env, simply write the offset of
> > [undefined] into the <next> location and then write a new env lump.
> >    <next><crc><env><NUL> <next><crc><env><NUL>[undefined]
> >     ^^^^ offset of -----> ^^^^ 0xFFFFFFFF
> 
> using a crc of 0x00000000 accomplishes the same thing and retains env format

No, this is not the same. With the offset, you can jump  directly  to
the  next  block;  with  just a "valid" flag you have to scan invalid
copy sequentially to find  the  end  -  especially  on  EEPROM  based
storage this is painfully slow (see
http://www.denx.de/wiki/DULG/AN2004_11_BootTimeOptimization).


Best regards,

Wolfgang Denk

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