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TP-LINK MR3020 prototype

This prototype is heavily based on the previous TPLINK 703N prototype, but avoids the need for a USB to serial adapter and USB hub.

Do not use the MR3020 for further prototypes. Instead use a GL-AR150, and see the Mesh Extender 2 prototyping page.


    • 32MB RAM
    • 4MB FLASH
    • serial port header
    • USB port
    • 802.11N Atheros 9k WiFi
    • 400MHz MIPs processor
  • SanDisk Cruzer Fit™ tiny USB memory stick

3D Printable Case

Thanks to Musti, we now have a 3D printable case for the Mesh Extender:

Here are the STL files for printing your own Mesh Extender case:


Images and related details for these cases:

images.tgz photos.tgz servalcase-mr3020-documentation.pdf

Hardware Assembly

  1. Remove lid by following the instructions at
  2. Remove the PCB
  3. Drill two holes on the top edge of the case to accomodate the RFD900 radio (6.5mm holes 20mm apart, centred approximately 9mm in from the top edge and the first hole starting approximately 20mm in from the left edge. I will supply a photo that makes this clearer).
  4. If you have obtained a normal RFD900, desolder the 16pin header. Ask RFDesign if they can supply it without the header installed in the first place, as it saves a bit of effort. They may or may not be able to depending on where they are in their manufacturing cycle, but the more people ask, the more they are likely to stock them this way.
  5. Solder a 4-pin ribbon cable between the MR3020 PCB and RFD900 radio connecting 5v, GND, TX and RX lines appropriately. See photo for pictorial explanation.

Firmware Installation (the new way)

Perform the following steps on a Linux box, but first …


Because of the inherent risk of human error when instructing the scripts to format and repartition memory sticks, we recommend that you use an old laptop or similar, and dedicate it to this process, so that you do not endanger your data.

MR3020 Instructions

  1. Make sure you have git, csh and expect installed

Depending on your Linux distribution, something like the following should suffice:

$ sudo yum install csh expect git

Alternatively you may need to use

$ sudo apt-get install csh expect git
  1. Download the Mesh Extender Builder software
$ git clone --quiet
  1. Build the OpenWRT image (this will download a lot of stuff the first time you run it, but you can re-run it quickly there after if you change something).
$ cd mesh-extender-builder
$ ./make_image
  1. Build the serval.up file
$ ./gather-image-files
  1. Insert the USB memory stick into the installation computer, noting its device name(can be found by typing “df” into the console), then unmount all the device partitions, then partition it using the following script, replacing deviceid with the Linux disk device, e.g., sdf. MAKE SURE YOU GIVE IT THE RIGHT DEVICE OR IT MIGHT TRY TO REPARTITION YOUR HARD DRIVE!
$ umount /dev/deviceid
$ ./ deviceid
  1. Remove and reinsert the USB memory stick so that the kernel notices the new partition table.
  2. Unmount the USB partitons again
  3. Populate the USB memory stick, again replacing deviceid with the right device, e.g., sdf. MAKE SURE YOU GIVE IT THE RIGHT DEVICE OR IT MIGHT ERASE THE PARTITIONS ON YOUR HARD DRIVE!
$ ./populate-memory-stick deviceid
  1. Unplug the USB memory stick and insert it into the MR3020 that is to become a mesh extender.
  2. Power up the MR3020, and connect it via ethernet to the installation machine, and wait a couple of minutes for it to boot up.
  3. If the MR3020 is still running the stock firmware, flash it this way:
$ ./flash-virgin-mr3020

You may need to specify the IP address on the command line if the script doesn't auto-detect the IP address. The most likely address is

  1. If the MR3020 already has OpenWRT, flash it this way. (You might need to boot the Mesh Extender into fail-safe mode first.)
$ ./reflash-mesh-extender

You may need to specify the IP address on the command line if the script doesn't auto-detect the IP address. The most likely address is or, e.g.:

$ ./reflash-mesh-extender

The MR3020 should reboot as a fully functional Mesh Extender.


SSH access

First thing to make sure of is that the noroot file has been deleted on the USB stick. Once this has been done use

$ ssh root@

If this works you should be greeted by a splash screen showing serval version and some other details.\

From this you can check if the serval node is functioning properly by using

root@ $ servald status

this will return either a few lines saying the status and should contain a line saying whether it is running or it will return a message saying servald is not found. If the latter is what is displayed delete noroot and reboot the mesh node with

$ rm /dos/noroot
$ reboot

The serval node should reboot and work once it has rebooted.

Changing name of the device

This is useful as it allows you to identify specific nodes if a few different ones are within range of each other rather than using sid or the phone number.

servald keyring set did `servald id self | tail -1` "Phone number" "Name"

This line allows the user to set the phone number and the name of the device for easy identification.

Disabling noroot lockout


ssh into the node using the above method. Once you have access use the following to navigate to the folder which contains the script that produces the noroot file.Then open the script in Vi

$ cd /etc/init.d
$vi dropbear

Find the two lines in this script that are as follows

passwd -l root # lock
[ -e /dos/noroot ] && return 1

and comment them out by adding a # to the front as follows

# passwd -l root # lock
# [ -e /dos/noroot ] && return 1

Once this has been done you will have root access at all times without having to delete noroot However it is a good idea to change the root password after doing this to discourage unauthorized access. this is achieved by using

$ passwd

Enabling SSH on a Mesh Extender

Remember if you wish to ssh to the Mesh Extender to power it down, remove the USB memory stick and insert it into any computer, and delete the NOROOT file from the FAT file system partition, and reinsert it into the Mesh Extender. ssh as root with password root will now be available until next reboot.


Sysupgrade not found

This means that the openwrt currently on the router cannot find the sysupgrade file

  1. Download the sysupgrade image for the router you are flashing from this list
  2. navigate to the folder where the image is located
  3. use the following to get the image onto the routers RAM
$ scp openwrt-ar71xx-generic-tl-mr3020-v1-squashfs-sysupgrade.bin root@
  - ssh into the router then use the following command to flash the sysupgrade image
# sysupgrade -v /tmp/openwrt-ar71xx-generic-tl-mr3020-v1-squashfs-
  1. Follow the serval instructions for your device to reflash serval to the device

Cannot ssh into the device

There can be a few diffferent causes for this issue.


This occurs when a root password hasn't been set on the device

  1. Telnet into the device
  2. set the root password
$ telnet
# passwd
  1. after this reboot the device and check if the ssh is working if not try the failsafe route


  1. change your computer from DHCP to static ip with an address of and subnet
  2. boot your router into failsafe mode e.g. TP-Link models can be booted into failsafe by holding the reset button once the light starts blinking on boot
  3. telnet into the router
$ telnet
  1. mount the JFSS2 partition to allow you to edit the password or other files that could be causing the issues with
# mount_root
  1. set the passwd if you forgot your password
# passwd
  1. Reset the router to stock openwrt if issue is not password related by using
# firstboot
  1. Once this is done reboot the router into normal mode using
# reboot -f

After this you will need to change your network settings back to dhcp to connect to the router through telnet/ssh

Firmware Installation (the old way)

  1. Download mesh extender firmware installation tools from (once only):
    $ cd ~/src
    $ git clone --quiet
    $ cd mesh-extender
    $ ls -a
    .  ..  .git  mr3020
  2. Partition the USB memory stick in any computer to have exactly three partitions of any size (this is to work around a bug when running fdisk on OpenWRT and creating partitions, where it doesn't create the /dev/ entries until after reinsert or reboot).
  3. Plug the MR3020 into the Ethernet jack on your workstation and activate the Ethernet port:
    • the MR3020 is a DHCP server, so your workstation's Ethernet port must be configured to obtain an IP using DHCP
    • if the MR3020 assigns your workstation an IP in the subnet 192.168.1, then this is a virgin install (the TP-LINK MR3020 is still running its factory firmware)
    • if the MR3020 assigns your workstation an IP in the subnet 192.168.2, then the Mesh Extender firmware has already been installed
  4. Continuing in the same command line as above:
    $ cd mr3020
    $ ./0.install-openwrt
  5. Wait for the MR3020 to reboot, then:
    $ ./1.upgrade_openwrt
  6. Wait for the MR3020 to reboot again, then:
    $ ./2.install_mesh_extender
  7. Wait for router to reboot for a third time
  8. Kill the runservald process and run servald stop to stop all servald processes.
  9. Run export TERM=xterm ; minicom -s and use minicom to configure to use /dev/ttyATH0 @ 57600, no hardware or software flow-control. Then use +++ to connect to radio and make sure it is happy. Adjust channels, frequencies, bit rates as required. More on this later. Required once only. We also hope to make this step redundant by making servald do this.

You should now have a working Mesh Extender.

We intend to refine and simplify this process further to make it easier for you to build your own mesh extenders. Of course you will need a pair to use them productively.

content/meshextender/prototyping_on_mr3020.1490648066.txt.gz · Last modified: 27/03/2017 13:54 by Paul Gardner-Stephen