Last updated: 2021/07/26

Working with USRP X310

Description

For this tutorial, we will now use two USRP X310s on ORBIT Sandbox 2 to transmit and receive a single frequency over the air to demonstrate the use of the USRP Hardware Drivers (UHD) with the USRP X310. This tutorial can be run on other USRP X310s available of the grid as well. For details on available USRPs on the grid, please see available USRP hardware in the grid.

As with any of these tutorials, it is much more productive to write the commands by hand rather than just copy-paste them. This will help memorize what is going on.

Hardware / Software Resources Utilized

We will be using the X310 radios in ORBIT Sandbox 2. One radio will be used to transmit, and the other to receive. For more information on these radios, please see the Sandbox 2 page.

We will use the following node image: baseline-gr-uhd4-rc.ndz which contains UHD 4.0.0 along with GNU Radio 3.8.

Set Up

Imaging

First, make sure you have Sandbox 2 reserved and are logged into the console over SSH. Please enable X11 forwarding, by using the -X flag (-Y if on Mac OS)

We should make sure that both of the nodes are turned off:

mpk2138@console:~$ omf tell -a offh -t node1-1,node1-2

Then, we want to image the nodes with the following commands:

mpk2138@console:~$ omf load -i baseline-gr-uhd4-rc.ndz -t node1-1

mpk2138@console:~$ omf load -i baseline-gr-uhd4-rc.ndz -t node1-2

Please note, it will take time to image the node, make sure that the first image process is finished before attempting to start the second.

Once both nodes are imaged, we can now turn them back on:

mpk2138@console:~$ omf tell -a on -t node1-1,node1-2

Accessing the Nodes

Give the node about a minute to turn on and be ready, and then SSH into the first node:

mpk2138@console:~$ ssh -X root@node1-1

Once you have SSH'd into node1-1, open a second SSH session and login to the Sandbox 2 console as before. On that new SSH session, SSH into the other node:

mpk2138@console:~$ ssh -X root@node1-2

At this stage, you should have two SSH windows open, each logged into one of the two nodes.

Configuring the Network Interface

Each node is physically connected to one USRP X310 over a 10 Gbps Ethernet connection. However, the default network card interface configuration will need to be changed so that the node can communicate to the correct IP address.

The USRP X310 uses a default IP address of 192.168.40.2 on its first 10 Gbps interface, which is the interface being used to connect to the node. So on both nodes, run the following command to setup the network interface to use the correct IP address:

root@node1-X:~# ifconfig enp1s0 192.168.40.1

By setting the IP address of the interface named enp1s0 on the node to 192.168.40.1 and using the default subnet mask of 255.255.255.0, we are then able to communicate with any device with an IP between 192.168.40.2 and 192.168.40.254 using that interface. Since the USRP X310 has IP address 192.168.40.2 and is connected to interface enp1s0, we can now communicate with it. Confirm this with the following command:

root@node1-X:~# uhd_find_devices

This should yield the following output:

[INFO] [UHD] linux; GNU C++ version 7.5.0; Boost_106501; UHD_4.0.0.0-25-g1a34ba8a
--------------------------------------------------
-- UHD Device 0
--------------------------------------------------
Device Address:
    serial: 30F10F9
    addr: 192.168.40.2
    fpga: HG
    name: 
    product: X310
    type: x300

Please ensure this works before proceeding.

Setting up GNU Radio

To make sure GNU Radio can start, please run the following two commands on each node to point GNU Radio to the correct Python installation directories:

root@node1-X:~# export PYTHONPATH=/usr/local/lib/python3/dist-packages/:$PYTHONPATH

root@node1-X:~# export LD_LIBRARY_PATH=/usr/local/lib/:$LD_LIBRARY_PATH

Now we set the network card read and write buffer size to the maximum size possible:

root@node1-X:~# sudo sysctl -w net.core.wmem_max=24862979

root@node1-X:~# sudo sysctl -w net.core.rmem_max=24862979

Building the GNU Radio Flowgraph

See the troubleshooting section below for a common error and how to fix it.

Start GNU Radio on node1-1:

root@node1-1:~# gnuradio-companion

The GNU Radio interface should show up on your local machine. The goal is to build a flowgraph that looks like this:

Troubleshooting

You may run into the following error when running the experiment:

[INFO] [X300] X300 initialization sequence...
Error: RuntimeError: Expected FPGA compatibility number 38, but got 36:
The FPGA image on your device is not compatible with this host code build.
Download the appropriate FPGA images for this version of UHD.
Please run:

 "/usr/local/lib/uhd/utils/uhd_images_downloader.py"

Then burn a new image to the on-board flash storage of your
USRP X3xx device using the image loader utility. Use this command:

"/usr/local/bin/uhd_image_loader" --args="type=x300,addr=192.168.40.2"

For more information, refer to the UHD manual:

 http://files.ettus.com/manual/page_usrp_x3x0.html#x3x0_flash

This is basically saying that the FPGA on the USRP X310 is a different version than that expected by UHD. To fix this issue, simply follow the commands as stated:

root@node1-X:~# /usr/local/lib/uhd/utils/uhd_images_downloader.py

root@node1-X:~# /usr/local/bin/uhd_image_loader --args="type=x300,addr=192.168.40.2"

Upon running the second command, you should see the following output:

[INFO] [UHD] linux; GNU C++ version 7.5.0; Boost_106501; UHD_4.0.0.0-25-g1a34ba8a
Unit: USRP X310 (30F110A, 192.168.40.2)
FPGA Image: /usr/local/share/uhd/images/usrp_x310_fpga_HG.bit
-- Initializing FPGA loading...successful.
-- Loading HG FPGA image: 0% (0/121 sectors)

Do not do anything on the node while this is running. An incomplete FPGA imaging process will brick the USRP X310 and render it totally unusable.

When it has completed, exit the node:

root@node1-X:~# exit

Once back in the console, power cycle the node using OMF. You can now log back into the node over SSH and continue on by setting up the network interface again.

The "imaging" outlined here is a very different procedure to "imaging" the node with a .ndz file. When imaging a node with a .ndz file, we are basically overwriting the hard drive with a backup. Imaging an FPGA on a USRP (or any FPGA in general) is the process of loading a new digital circuit configuration onto the FPGA's EEPROM - a much more delicate process which is why it must complete without disturbance.