Unable to set environment variable in compile time of uBoot - yocto

Question

I am trying to bring net-console in uboot. For that, I first added 'ncip' in "uboot-imx/include/configs/imx8mm_evk.h" as following. Later, DFMC_SWUG is called at the end of CONFIG_EXTRA_ENV_SETTINGS.
#define DFMC_SWUG \
"setenv ncip 192.168.100.98 \0" \
"ethaddr=00:80:A3:CA:B5:77 \0" \
"swugip=192.168.100.16 \0" \
"ipaddr=192.168.100.2 \0" \
"serverip=192.168.100.16 \0" \
"bootdelay=3\0" \
#define CONFIG_EXTRA_ENV_SETTINGS \
CONFIG_MFG_ENV_SETTINGS \
JAILHOUSE_ENV \
"script=boot.scr\0" \
--
--
--
"fi;\0" \
DFMC_SWUG
Interestingly, I was able to set 'ethaddr', "swugip" and other variables except "ncip". I guess, I am doing some formatting mistakes in line --> "setenv ncip 192.168.100.98 \0" \
Later I tried setting some dummy variables named dummy_var_1, dummy_var_2, dummy_var_3. Even they are not getting set.
Can some one please guide me here?

Answer 1

The U-Boot environment consists of strings in the form <env_var>=<string value><null> (and preceded with a CRC32 word).
So strings for environment variables have to conform to that template when predefining them in code using CONFIG_EXTRA_ENV_SETTINGS.
That also means that you cannot install raw commands in the environment such as "setenv ncip 192.168.100.98 \0".
The U-Boot documentation is clear on this topic.
Note the last sentence of the warning.
- Default Environment:
CONFIG_EXTRA_ENV_SETTINGS
Define this to contain any number of null terminated
strings (variable = value pairs) that will be part of
the default environment compiled into the boot image.
For example, place something like this in your
board's config file:
#define CONFIG_EXTRA_ENV_SETTINGS \
"myvar1=value1\0" \
"myvar2=value2\0"
Warning: This method is based on knowledge about the
internal format how the environment is stored by the
U-Boot code. This is NOT an official, exported
interface! Although it is unlikely that this format
will change soon, there is no guarantee either.
You better know what you are doing here.
I did try "ncip=192.168.100.98" ...
That looks almost correct, but needs the explicit null terminator.
Interestingly, I was able to set 'ethaddr', "swugip" and other variables except "ncip".
...
Later I tried setting some dummy variables named dummy_var_1, dummy_var_2, dummy_var_3. Even they are not getting set.
You have only provided your vague summations of the actual results.
Did you inspect any .o object files to check what text strings were stored?
Did you perform a strings u-boot.bin | less on the U-Boot image file to review the default environment embedded in the image?
Note that you could be making an additional mistake.
The environment variables defined in CONFIG_EXTRA_ENV_SETTINGS will only (initially) exist in the default environment of U-Boot.
You have been very parsimonious with details, and neglect to mention your setup. If there is an existing and valid stored environment in the nonvolatile boot medium, then specific procedures need to be performed to suppress the existing stored environment in order to revert to the default environment with the "new" environment variables.
Failure to disable/delete an existing stored environment when installing a new/different version of u-boot.bin will conceal the new/different default environment and all the new/different variables in it. If U-Boot does not issue the message similar to:
Loading Environment from xxx... *** Warning - bad CRC, using default environment
then you can be assured that your new/different environment variables are not in the current runtime environment.
IOW you want to see this warning message on (initial) boot.

Answer 2

If one wishes to compile u-boot with netconsole then following changes have to be done for the file in uboot-imx/include/configs/imx8mm_evk.h
Add ‘ncip’ i.e., IP address of the computer/device which holds net console along with other network settings. Please note that every variable in u-boot will be null terminated string.
Also add a variable (in following case it is dfmcswug) which will set the standard input, output and error reporting over netconsole. This variable will be called later.
Include the DFMC_SWUG macro inside CONFIG_EXTRA_ENV_SETTINGS macro so that our new settings will be added along with other environmental settings.
Add dfmcswug variable in CONFIG_BOOTCOMMAND so that it will get executed by tool chain during run time.
With the above steps, u-boot should output its console over netconsole.
On the client-side use Or similar.
nc -u -l -p 6666 <ip_address_of_uboot_host>