[U-Boot] macro substitution - can someone explain please

[Mike Frysinger]

On Friday 23 October 2009 08:25:00 David Collier wrote:
> If I put the following line in my board.h file
> 
> #define CONFIG_RAMBOOTCOMMAND						\
>   "ping ${serverip} && tftp && bootm ${fileaddr}"

start with the binary.  run `strings` on your u-boot.bin (or whatever you're 
using) and see what ramboot is set to.

> then when I do PRINTENV I see
> 
> ramboot=ping ${serverip} && tftp && bootm 0x10400000
> 
> so clearly at some point the text ${fileaddr} has been substituted,
> whereas ${serverip} hasn't
> 
> If I retype the line at the command prompt, the ${fileaddr} appears as I
> wished, so it must be happening diring compile and so on.

i doubt variable expansion is happening during compile.  it isnt like gcc 
knows how to expand shell variables in C code.
-mike
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