[U-Boot-Users] embedding environment by hand

[Mike Frysinger]

first a little background ... the Blackfin processor has a custom object 
format for booting code (called a "loader file" or "LDR" for short).  this 
custom object format is what actually gets burned into say parallel or spi or 
nand flash.  i have to hope that the Blackfin processor isnt alone in having 
a custom object format ;), so hopefully the changes i propose here will be 
useful to others.

the exact object format is irrelevant here, but the point is that while the 
environment is actually embedded inside of the LDR image, it cannot be 
embedded with the standard method of creating the data array "environment" in 
environment.c and making sure the environment.o object gets linked at an 
exact offset.  this is because we take the u-boot.bin and run it through 
another utility to get u-boot.ldr.  the offsets in u-boot.bin do not 
correlate in any way to the offsets in u-boot.ldr nor can they as the LDR 
format may different drastically by processor.

the utility that generates the u-boot.ldr has the ability to reserve space 
inside of the final image.  so in the board configuration file, we say the 
environment lives at an offset of 0x4000 (to correspond to one of the flash 
sectors) of size say 0x2000.  the utility is then told to generate space at 
an offset in u-boot.ldr at offset 0x4000 of size 0x2000.  now the u-boot.ldr 
can be burned into flash without a problem and saving of the environment is 
OK.

however, the initial u-boot.ldr is generated without the default environment 
programmed into it.  so what i'd propose is to introduce a new 
define "ENV_IS_EMBEDDED_CUSTOM" and add a new flag to the envcrc helper.  
this would allow the environment.o linked into u-boot.bin to be empty and we 
can use envcrc helper to extract the environment blob so that the blob can be 
passed to extrenal utilities for embedding.  the patch attached accomplishes 
both of these things.
-mike
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