U-Boot has a nice feature - the ability to automatically assign the networking parameters and load a boot image to the board's RAM.

Step through the following procedure in order to add DHCP client to U-Boot:

1. Define the CONFIG_CMD_DHCP configuration parameter in the U-Boot configuration file for your board (u-boot/include/configs/<board>.h):

...
#define CONFIG_CMD_DHCP
...

Refer to the u-boot/README.u-boot file and the u-boot/doc/ directory for more DHCP-related options.

2. Build the U-Boot image as described in the "U-Boot Build" section of the Starter Kit Guide or the Board Support Package Guide.
3. Upgrade U-Boot on your board as described in Section 5.3.5 of the Linux Cortex-M User's Manual.
4. Specify the boot image filename:

U-Boot> setenv bootfile psl/m2s/networking.uImage
U-Boot> saveenv

5. Connect to the serial console, reset the board and stop auto-boot by hitting any key. At the U-Boot prompt, run the dhcp command to invoke DHCP client to obtain an IP address and boot the board:

U-Boot>dhcp
BOOTP broadcast 1
DHCP client bound to address 172.17.11.49
...
TFTP from server 172.17.0.1; our IP address is 172.17.11.49
Filename 'psl/m2s/networking.uImage'.
Load address: 0xa0007fc0
Loading: #################################################################
#################################################################
###########################
done
Bytes transferred = 2290944 (22f500 hex)
U-boot>

6. Now, putting it all together to make the board boot automatically:

U-Boot> print netboot
netboot=tftp ${loadaddr} ${image};run addip;bootm
U-Boot> setenv netboot dhcp\;run addip\;bootm
U-Boot> print netboot
netboot=dhcp;run addip;bootm
U-Boot> print bootcmd
bootcmd=run flashboot
U-Boot> setenv bootcmd run netboot
U-Boot> saveenv
Saving Environment to SPI Flash...
Erasing SPI flash...Writing to SPI flash...done
U-Boot>re

U-Boot 2010.03-00030-ga697c91-dirty (Nov 19 2014 - 13:34:28)
...
BOOTP broadcast 1
DHCP client bound to address 172.17.11.49
...
TFTP from server 172.17.0.1; our IP address is 172.17.11.49
Filename 'psl/m2s/networking.uImage'.
Load address: 0xa0007fc0
Loading: #################################################################
#################################################################
###########################
done
Bytes transferred = 2290944 (22f500 hex)
## Booting kernel from Legacy Image at a0007fc0 ...
Image Name: Linux-2.6.33-arm1
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 2290880 Bytes = 2.2 MB
Load Address: a0008000
Entry Point: a0008001
Verifying Checksum ... OK
Loading Kernel Image ... OK
OK

Starting kernel ...

Linux version 2.6.33-arm1 (psl @ocean.emcraft.com) (gcc version 4.4.1 (Sourcery G++ Lite 2010q1-189) ) #5 Mon Dec 9 20:29:17 +0400 2013
...
IP-Config: Complete:
device=eth0, addr=172.17.11.49, mask=255.255.0.0, gw=172.17.0.137,
host=m2s-fg484-som, domain=, nis-domain=(none),
bootserver=172.17.0.1, rootserver=172.17.0.1, rootpath=
Freeing init memory: 912K
eth0: link up (100/full)
init started: BusyBox v1.17.0 (2013-12-09 20:27:30 +0400)
~ #