[U-Boot] where *precisely* is u-boot's environment stored?

[Robert P. J. Day]

  kind of embarrassed that i don't know the answer to this but, short
form of question, when i build a u-boot.bin and copy it to NOR flash
on my target board, where is the environment stored such that user
space fw_printenv and fw_setenv utilities can get at them?

  longer form of question: i just used yocto project to build for my
MPC8315E-RDB target board, and one of the artifacts generated was
"u-boot.bin", apparently ready for copying to NOR flash on this board,
NOR flash being at 0xfe000000. i poked around trying to figure out
where the environment was stored in that image, and i found the
following in include/env_default.h:

  ... snip ...
  const uchar default_environment[] = {
  #endif
  #ifdef  CONFIG_ENV_CALLBACK_LIST_DEFAULT
        ENV_CALLBACK_VAR "=" CONFIG_ENV_CALLBACK_LIST_DEFAULT "\0"
  #endif
  #ifdef  CONFIG_ENV_FLAGS_LIST_DEFAULT
        ENV_FLAGS_VAR "=" CONFIG_ENV_FLAGS_LIST_DEFAULT "\0"
  #endif
  #ifdef  CONFIG_BOOTARGS
        "bootargs="     CONFIG_BOOTARGS                 "\0"
  #endif
  #ifdef  CONFIG_BOOTCOMMAND
        "bootcmd="      CONFIG_BOOTCOMMAND              "\0"
  #endif
  ... etc etc ...

i then checked u-boot.sym and found:

  fe04c920 g     O .text  00000389 default_environment

and if i "hexdump -C" the "u-boot.bin" file, sure enough, there it is,
the apparent beginning of the default environment at 0x0004c920:

0004c900  8d ef 02 2d 25 2e 2a 73  00 00 00 00 25 73 25 64  |...-%.*s....%s%d|
0004c910  2c 25 64 00 70 61 72 74  69 74 69 6f 6e 00 00 00  |,%d.partition...|
0004c920  62 6f 6f 74 63 6d 64 3d  73 65 74 65 6e 76 20 62  |bootcmd=setenv b|
0004c930  6f 6f 74 61 72 67 73 20  72 6f 6f 74 3d 2f 64 65  |ootargs root=/de|
0004c940  76 2f 6e 66 73 20 72 77  20 6e 66 73 72 6f 6f 74  |v/nfs rw nfsroot|
0004c950  3d 24 73 65 72 76 65 72  69 70 3a 24 72 6f 6f 74  |=$serverip:$root|
... and on and on ...

  so AFAICT, the default_environment[] ends up in the executable (and,
consequently, in flash) i'm assuming based on wherever the linker
places it based on the "u-boot.lds" file, correct?

  however, if i look at the defn file for this target board,
include/configs/MPC8315ERDB.h, i can see the various config settings
defining where the environment resides, things like
CONFIG_ENV_IS_IN_FLASH, CONFIG_ENV_ADDR and so on:

  #if !defined(CONFIG_SYS_RAMBOOT)
        #define CONFIG_ENV_IS_IN_FLASH  1
        #define CONFIG_ENV_ADDR         \
                        (CONFIG_SYS_MONITOR_BASE + CONFIG_SYS_MONITOR_LEN)
        #define CONFIG_ENV_SECT_SIZE    0x10000 /* 64K(one sector) for env */
        #define CONFIG_ENV_SIZE         0x2000

and if i build the package u-boot-fw-utils to get the user space
utilities "fw_printenv" and "fw_setenv", that package needs to be told
where the environment is stored, and that's based on what it gets from
the board's header file, which in this case defines:

#define CONFIG_SYS_MONITOR_LEN  (384 * 1024) /* Reserve 384 kB for Mon */

which represents an env offset of 0x00060000 into flash.

  so what is the correlation between those two addresses? there's the
actual address of default_environment[] based on where the linker puts
it (0xfe04c920), as opposed to where fw-utils will (apparently) look
for the environment (0xfe060000). what's the connection here?

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
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