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 atinclude/configs/ccimx6ulsbc.h
andinclude/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
.
Digi Embedded Yocto 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 two entries in the form: Device name, offset, size.
The first entry must point to the U-Boot environment location.
The second must point to its redundant copy.
If both copies are set to the same offset, an automatic mechanism custom to Digi U-Boot implementations determines the first good sectors where each copy lives. This mechanism makes better use of NAND sectors and improves space allocation for potential bad blocks.
# Configuration file for fw_(printenv/setenv) utility.
# Up to two entries are valid, in this case the redundant
# environment sector is assumed present.
# If both copies are set to the same offset, an automatic mechanism will
# determine the first good sectors where each copy lives, skipping bad blocks.
# Device name Offset Size Erase-size No.Blocks
/dev/mtd1 0x0 0x20000 0x20000 24
/dev/mtd1 0x0 0x20000 0x20000 24
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:
MAC addresses
Variable | Description | Flags |
---|---|---|
|
MAC address of the first wired Ethernet interface |
change-default |
|
MAC address of the second wired Ethernet interface if there is one |
change-default |
|
MAC address of the Wi-Fi interface |
change-default |
|
MAC address of the Bluetooth interface |
change-default |
About flags
|
Digi programs the MAC addresses of the ConnectCore 6UL during manufacturing and saves them in the U-Boot environment on the NAND.
You can find the Digi-assigned MAC address on the ConnectCore 6UL module label. See Determine Digi MAC addresses for more information.
Wireless virtual MAC addresses
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 |
---|---|---|
|
MAC address of virtual wireless interface 1 |
change-default |
|
MAC address of virtual wireless interface 2 |
change-default |
|
MAC address of virtual wireless interface 3 |
change-default |
Module variant
Variable | Description | Flags |
---|---|---|
|
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 |
---|---|---|
|
Version number of the carrier board |
write-once |
|
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.
Determine Digi MAC addresses
Sequential MAC address scheme
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.
Determine MAC addresses
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
If your SOM has a second Ethernet MAC address:
=> printenv eth1addr
To get Wi-Fi MAC address:
=> printenv wlanaddr
To get Bluetooth MAC address:
=> printenv btaddr