[U-Boot-Users] CFG_ENV_SECT_SIZE != CFG_ENV_SIZE

[U-Boot-Users] CFG_ENV_SECT_SIZE != CFG_ENV_SIZE

[Robin Getz]

In [u-boot.git] / common / env_flash.c around line 171 there is a 

#if CFG_ENV_SECT_SIZE > CFG_ENV_SIZE

to be able to mix other data, and the environment info. (Where 'other data' 
could be U-Boot code).

However, in an email a few days ago:

On 3/26/07, Wolfgang Denk <wd@denx.de> wrote:
 > In message <46040C60.5070505@inaccessnetworks.com> you wrote:
 > > I have a flash chip with equally sized sectors and I don't want to waste
 > > an entire sector for the environment. I have the u-boot environment
 > > embedded in the u-boot sector. The declarations in my board file are:
 >
 > Do not do this. Do NOT do this. DO NOT DO THIS.
 >
 > Please never mix U-Boot code and environment data in one sector.
 > Always use a separate sector (or two) for the environment.

If that is the recommendation (which is fine), why have this code snippet in 
there, and not add something like:

#error Do not do this. Do NOT do this. DO NOT DO THIS.

:)

This is just curiosity - no other reason.
-Robin

[U-Boot-Users] CFG_ENV_SECT_SIZE != CFG_ENV_SIZE

[Wolfgang Denk]

In message <200703271327.00147.rgetz@blackfin.uclinux.org> you wrote:
> In [u-boot.git] / common / env_flash.c around line 171 there is a 
> 
> #if CFG_ENV_SECT_SIZE > CFG_ENV_SIZE
> 
> to be able to mix other data, and the environment info. (Where 'other data' 
> could be U-Boot code).

No, this is NOT the intention.

The intention is to allow for having  a  resonable  envrionment  size
(say  8...16kB)  even  if  you  have big flash sectors (like 256kB or
more). This is needed to avoid slow bot times because  otherwise  you
would  laways  have  to compute the CRC checksums for one or two such
big sectors when all you want to protect are a few kB of data.

> If that is the recommendation (which is fine), why have this code snippet in 
> there, and not add something like:
> 
> #error Do not do this. Do NOT do this. DO NOT DO THIS.

Because it is a very useful thing to  have,  just  for  a  completely
different  purpose  (i.  e.  leave  the  rest of the sector empty and
unused).

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH, HRB 165235 Munich, CEO: Wolfgang Denk
Office:  Kirchenstr. 5,       D-82194 Groebenzell,            Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Mike's Law: For a lumber company employing two men and a cut-off saw,
the marginal product of labor for any number  of  additional  workers
equals  zero  until the acquisition of another cut-off saw. Let's not
even consider a chainsaw.
- Mike Dennison [You could always  schedule the saw, though - ed.]

[U-Boot-Users] CFG_ENV_SECT_SIZE != CFG_ENV_SIZE

[Detlef Vollmann]

Robin Getz wrote:
> In [u-boot.git] / common / env_flash.c around line 171 there is a
> 
> #if CFG_ENV_SECT_SIZE > CFG_ENV_SIZE
> 
> to be able to mix other data, and the environment info. (Where 'other data'
> could be U-Boot code).
> 
> However, in an email a few days ago:
> 
> On 3/26/07, Wolfgang Denk <wd@denx.de> wrote:
>  > In message <46040C60.5070505@inaccessnetworks.com> you wrote:
>  > > I have a flash chip with equally sized sectors and I don't want to waste
>  > > an entire sector for the environment. I have the u-boot environment
>  > > embedded in the u-boot sector. The declarations in my board file are:
>  >
>  > Do not do this. Do NOT do this. DO NOT DO THIS.
>  >
>  > Please never mix U-Boot code and environment data in one sector.
>  > Always use a separate sector (or two) for the environment.
> 
> If that is the recommendation (which is fine), why have this code snippet in
> there, and not add something like:
> 
> #error Do not do this. Do NOT do this. DO NOT DO THIS.
There is other data that you can put into the same sector as the
U-Boot environment.
In our BSP, we use it for data written there at production,
in another project we use it for data that is read from Linux
but must stay outside the Linux kernel and filesystem image.

 Detlef

-- 
Detlef Vollmann   vollmann engineering gmbh
Linux and C++ for Embedded Systems    http://www.vollmann.ch/
Linux for PXA270 Colibri module: http://www.vollmann.ch/en/colibri/