The U-Boot environment is a block of memory in persistent storage. It is used to store variables in the form name=value.

## Where is the U-Boot environment?

The ConnectCore 6UL reads the U-Boot environment (including the MAC addresses) from a partition called environment in the NAND flash. If it does not find a valid environment on the NAND, U-Boot uses a hard-coded default environment:

• The environment is located at the offset determined by constant CONFIG_ENV_OFFSET in U-Boot source code at include/configs/ccimx6ulsbc.h and include/configs/ccimx6ulstarter.h.

• The size of the environment is determined by constant CONFIG_ENV_SIZE at the same header file.

• There is a back-up copy of the environment in the same NAND partition (where the original copy is) at the offset determined by constant CONFIG_ENV_OFFSET_REDUND in the same header file.

## Access U-Boot environment from Linux

You can access the U-Boot environment from a Linux application. In the U-Boot source tree, you can find the environment tools in the directory tools/env, which you can build with the following command:

`make env`

Digi Embedded Yocto also compiles this tool by default and installs it on your target’s root file system as two executable files:

• fw_printenv: to print the value of variables.

• fw_setenv: to set the value of variables.

The tools work with the configuration file /etc/fw_env.config, which must contain one or two entries in the form: Device name, offset, size. The first entry must point to the U-Boot environment location. The second (if present) must point to its redundant copy, for example:

/etc/fw_env.config
``````# Configuration file for fw_(printenv/setenv) utility.
# Up to two entries are valid, in this case the redundant
# environment sector is assumed present.
# Device name        Offset      Size
/dev/mtd1            0x0         0x20000
/dev/mtd1            0x20000     0x20000``````

## Append boot arguments to the kernel command line

You can use the extra_bootargs variables to append commands to the default kernel command line.

## Important U-Boot environment variables on the ConnectCore 6UL

The following U-Boot environment variables are worth mentioning:

Variable Description Flags

$ethaddr MAC address of the first wired Ethernet interface change-default$eth1addr

MAC address of the second wired Ethernet interface if there is one

change-default

$wlanaddr MAC address of the Wi-Fi interface change-default$btaddr

MAC address of the Bluetooth interface

change-default

 About flags Variables with write-once flag are protected and will not be overwritten by setenv or env default commands (unless manually forced with -f option). Variables with change-default flag can only be written once using setenv command (unless manually forced with -f option).

Digi programs the MAC addresses of the ConnectCore 6UL during manufacturing and saves them in the U-Boot environment on the NAND.

The wireless interface on the ConnectCore 6UL module allows you to define up to three optional virtual interfaces so that the platform can run concurrently as station, p2p, and SoftAP. Digi neither reserves nor programs unique MAC addresses for these virtual interfaces. A user who wishes to assign unique MAC addresses to such virtual interfaces can use the following U-Boot environment variables:

Variable Description Flags

$wlan1addr MAC address of virtual wireless interface 1 change-default$wlan2addr

MAC address of virtual wireless interface 2

change-default

$wlan3addr MAC address of virtual wireless interface 3 change-default ### Module variant Variable Description Flags$module_variant

Variant ID code for the System-On-Chip

write-once

During start-up, U-Boot automatically sets this variable to the ConnectCore 6UL System-On-Chip variant ID number (a hexadecimal code programmed in the SOM one-time programmable bits).

### Carrier board version and ID

Variable Description Flags

$board_version Version number of the carrier board write-once$board_id

ID number of the carrier board

write-once

During start-up, U-Boot automatically sets these variables to the carrier board’s version and ID numbers (decimal numbers programmed in the SOM one-time programmable bits). See Carrier board version and ID.

Digi assigns MAC addresses according to a sequential scheme. The order of assignment depends on the available interfaces, but the scheme always respects the order Ethernet 1, Ethernet 2, Wi-Fi, Bluetooth and skips non-available interfaces.

You can determine the MAC addresses for your device either by reading the Ethernet MAC off the label and using the scheme to calculate subsequent addresses, or by reading them from your device. To read the stock environment variables from the device using the `printenv` command executed at the U-Boot prompt:

To get First Ethernet MAC address:

`=> printenv ethaddr`

`=> printenv eth1addr`
`=> printenv wlanaddr`
`=> printenv btaddr`