Testing the cape without BBB

Although OpenVLC 1.3 cape is designed to be connected to the BBB, its functionalities can be tried without one. This step is not essential and requires additional devices such as a waveform generator or an oscilloscope. But it can be useful to test its correct functioning before plugging it to the BBB and to avoid possible damages to the board.

TX mode

Set the connections shown in the image below.

 Once it’s plugged, connect the 5 V power supply and that’s all.


ATTENTION: Be careful not to bend the components that stand out when you press or pull the cape.



​Setting up the VLC link


There are two parts in the TX/RX, the kernel driver and the PRU code. Follow these steps: 

  • In order to load the kernel driver, run the following command inside the Driver folder: sudo ./load_test.sh. With this script, you can change the IP taken by the interface. That’s the IP in the VLC network, so TX and RX must have different IPs (for example TX: 192.168.0.1 and RX 192.168.0.2).
  • ​Once the module driver is installed, make sure that proper paths and symbolic links have been made for the PRU compiler (clpru) and linker (lnkpru). The following commands can be used to this end:


​​          cd /usr/share/ti/cgt-pru
          sudo mkdir bin
          cd bin
          sudo ln -s /usr/bin/clpru clpru
          sudo ln -s /usr/bin/lnkpru lnkpru


  • Then go to the PRU folder, enter TX/RX and run sudo ./deploy.sh. This will boot up the PRUs with the code necessary to transmit and receive VLC data.


​​Working with the VLC link


Once you have done the steps above in TX and RX, you can start using VLC as a common network interface.

You could measure the achievable throughput by using the iperf tool. To this end, launch iperf in client mode at the TX (sudo iperf -c 192.168.0.2 -u -b 400k -l 800 -p 10001 -t 100) and in server mode at the RX (sudo iperf -u -l 800 -s -i3 -B 192.168.0.2 -p 10001). Make sure that TX and RX have different IPs and the IP of the RX (iperf server) is 192.168.0.2.

The image below shows the results of an iperf test at 2.5 meters of distance:​

 

Connect a 5 V power supply to the jack port. To emulate a transmission with OpenVLC 1.3 you can produce in the cape pin TX SIGNAL (P8_45 in BBB) a square wave between 0 and 3.3 V at 1 MHz. The LED should light on without any noticeable blinking. Modulated light can be measured with a fast light-sensing device (photodiode) connected to an oscilloscope.

To test constant illumination, connect TX SIGNAL to GND and the pin next to it (P8_46) to 3.3 V. The LED should provide similar illumination level than in the previous case.

RX mode

Set the connections shown in the image below.

Design of OpenVLC

The OpenVLC1.3 takes advantage of the programmable real time units (PRU) included in the BBB. This,and the new receiver design allow us to increase the transmission frequency to 1 MHz and, thus, the communication rate. One cape can work as Transmitter (TX) or Receiver (RX), but not at the same time.

Connect a 5 V power supply to the jack port. Produce a square wave between 0 and 3.3 V at 1 MHz at ADC CS, and a square wave between 0 and 3.3 V at 48 MHz at ADC SCLK. You can read the serial digital output from the ADC in the cape on pin RX SIGNAL.



Feedback


If you have doubts and questions about these instructions, please leave your message in our Google group: https://groups.google.com/forum/#!forum/openvlc

OpenVLC driver, firmware and hardware


Code and schematics are available at https://github.com/openvlc/openvlc


​​We don't plan to produce and distribute ourselves the boards in the near future, but if you are interested to produce them for the community at an affordable price, please contact us at openvlc.networks@imdea.org​​


Instructions

OpenVLC needs just a few components to work:


  1. BEAGLEBONE Black (BBB) Board (needs Rev C, AM3358BZCZ, produced from 2017; you need to connect an external 5V power supply to the BBB): cost $ 45 - $ 60; 
  2. OpenVLC1.3 cape:  the VLC front-end for transmission and reception. The latest changes include modulation with dimming support, and current-driven design (LED at higher current)
  3. OpenVLC1.3 driver: software code for MAC and PHY layer (implemented as Linux driver) and firmware (to control the programmable real time units (PRU) of the BBB)


(Note: we do have also the new OpenVLC1.4 version available on github. Nevertheless, it is currently in Beta version.) The software solution is implemented as a Linux driver that can communicate directly with the cape and the Linux networking stack. In OpenVLC, the VLC interface is set up as a new communication interface that can take advantage of the vast range of Linux tools.

Experimental Setup


These instructions assume you have two BBBs and two capes. In case you have only one cape, and you want to test its functionalities, check the section "Testing the cape without BBB" at the bottom of this page.


Creating the SD Card

​
We need to flash the BBB with a Debian image. To do that we need a SD Card with at least 4 GB. Follow these steps:


Flashing the BBB

Now that we have the SD Card ready with the image, we need to flash the BBB. Follow these steps:

  • With the power disconnected, insert the SD Card into the BBB and power it up with the USB cable.
  • Connect through SSH to the IP 192.168.7.2.
  • In order to run the OS on the SD Card, flash it into the BBB: go to /opt/scripts/tools/eMMC and run sudo ./bbb-eMMC-flasher-eewiki-ext4.sh 
  • Wait until the script of previous steps reports the following message: “eMMC has been flashed”. Once it finishes, disconnect the usb cable and with the BBB switched off, remove the SD Card.


Setting up the OS

The firsts steps are to prepare the beaglebone. This must be done in the OpenVLC board operating as TX as well as in the OpenVLC board operating as RX. These are the steps:

  • Disable the HDMI: The HDMI uses some PRU pins that we need. To disable the HDMI cape edit the uEnv.txt file: sudo nano /boot/uEnv.txt and uncomment the line: dtb=am335x-boneblack-emmc-overlay.dtb
  • Reboot the OpenVLC board. The HDMI is disable after rebooting.
  • Install the headers: Connect the beaglebone to the Internet, and then update with: sudo apt-get update
  • Then the board is ready to install the headers with: sudo apt-get install linux-headers-$(uname -r)
  • The code is in github at https://github.com/openvlc/openvlc​​. In Latest_Version subdirectory you will find the Driver (kernel) and PRU code folders. Just fetch them by using sudo git clone https://github.com/openvlc/OpenVLC, and copy them into the path "/home/Debian. 


​Connecting the cape


Connecting the cape to the BBB is quite easy. You just need to plug the cape to the correct pins as shown in the image below: