Emcraft Systems
4.4. Extension Interfaces
For description of the extension interfaces provided by the Emcraft Systems STM32F4 SOM
board refer to
Emcraft Systems STM32F4 SOM (System-On-Module) Hardware Architecture
.
For description of the extension interfaces provided by the Emcraft Systems SOM-BSB-EXT
baseboard refer to
Emcraft Systems SOM-BSB-EXT Baseboard Hardware Architecture
.
The above mentioned documents can be downloaded from the following page:
http://www.emcraft.com/som/stm32f4
5. STM32F4 SOM Board Linux Software Set-up
5.1. U-Boot Environment
When the STM32F4 SOM board is reset, the Linux bootstrap will proceed to boot the U-Boot
firmware from the built-in Flash printing the following output to the serial console:
U-Boot 2010.03-linux-cortexm-1.12.0 (Dec 9 2013 - 13:10:14)
CPU : STM32F4 (Cortex-M4)
Freqs: SYSCLK=168MHz,HCLK=168MHz,PCLK1=42MHz,PCLK2=84MHz
Board: STM-SOM Rev Rev 2.A, www.emcraft.com
DRAM: 32 MB
Flash: 16 MB
In: serial
Out: serial
Err: serial
Net: STM32_MAC
Hit any key to stop autoboot: 0
STM32F4X9-SOM>
U-boot makes use of the so-called environment variables to define various aspects of the
system functionality. Parameters defined by the U-boot environment variables include:
target IP address, target MAC address, address in RAM where a Linux bootable images will
be loaded, and many more. To examine the current settings of the environment variables,
run
printenv
from the U-Boot command interface.
U-Boot provides a command called
saveenv
that stores the up-to-date run-time environment
to the persistent storage, which will be the external Flash for the U-Boot configuration used
on the STM32F4 SOM board. You need to call
saveenv
any time when you want to copy
current settings of the environment variables to the persistent storage in Flash. This is how
you can write the current U-Boot environment to the external Flash:
STM32F4X9-SOM> saveenv
Saving Environment to Flash...
...
STM32F4X9-SOM>
5.2. Ethernet MAC Address
In Linux STM32F4, the MAC address of the Ethernet interface is defined by the
ethaddr
U-
Boot environment variable. The value of the MAC address can be examined from the U-Boot
command line monitor as follows:
STM32F4X9-SOM> printenv ethaddr
ethaddr=C0:B1:3C:88:88:88
STM32F4X9-SOM>
The STM32F4 SOM board comes with
ethaddr
set to a MAC address uniquely allocated for
the specific board. Given that each STM32F4 SOM board has a unique MAC address allocated
to it, there is no need to update the
ethaddr
variable (although it is possible to do so).
The MAC address can be changed by modifying the
ethaddr
variable as follows:
Emcraft Systems STM32F4 SOM Starter Kit Guide
8/12
Release 1.12.0