In case the original firmware needs to be restored. Firmware for the MR3220 V2.2 can be found here, select the most recent version (this guide uses TL-MR3220_V2_130423.zip):
http://www.tp-link.com/en/support/download/?model=TL-MR3220&version=V2
OpenWRT has a page for the MR3220: http://wiki.openwrt.org/toh/tp-link/tl-mr3420#mr3220.v2.x
At the time of writing (Sep. 2013), the MR3220 V2.2 requires works with the trunk version of OpenWRT only. For a fresh install, use the factory image:
(For an upgrade (of OpenWRT?) use the sysupgrade image: http://downloads.openwrt.org/snapshots/trunk/ar71xx/openwrt-ar71xx-generic-tl-mr3220-v2-squashfs-sysupgrade.bin)
Connect your computer to one of the LAN ports of the MR3220 and obtain an IP address via DHCP. Your Address should be something like 192.168.0.XXX, if the router is running TP-LINK firmware.
Reset factory defaults navigate to System Tools > Factory Defaults and clicking on Restore.
Install OpenWRT navigating to System Tools > Firmware Upgrade, upload openwrt-ar71xx-generic-tl-mr3220-v2-squashfs-factory.bin-factory.bin.
Wait for the upgrade to finish.
After the upgrade has finished, obtain a new IP address from the router.
The MR3220 works with the trunk version of OpenWRT only, trunk has no web interface preinstalled. Login via telnet:
telnet 192.168.1.1
Set the password for root, you will need to type your new password two times:
passwd root
This will disable access to the router via telnet, use SSH from now on to access the MR3220:
The trunk version of OpenWRT has no web interface preinstalled.
Make sure the router can connect to the internet. Then, update the list of packages with:
opkg update
And install LuCi with:
opkg install luci-ssl
In addition to luci-ssl, luci-theme-openwrt (or any other theme, opkg list luci-theme-*) must be installed, or the web interface will complain that no themes could be found:
opkg install luci-theme-openwrt
Start and enable the uhttpd web server (enabling it will start uhttpd automatically after each reboot):
/etc/init.d/uhttpd start && /etc/init.d/uhttpd enable
See if the web interface is working pointing your browser to http://192.168.1.1/.
Not enough space to install LuCi