glip  0.1.0-dev
The Generic Logic Interfacing Project
Nexys4 DDR UART Loopback Demo

This demo implements a loopback in the device. The seven segment display is used to show the current throughput in the loopback.

This demo assumes basic familiarity with Xilinx Vivado and using an FPGA.


For this demo you need:

Download and compile glip

If you have not done this before you need to download and build glip:

git clone
cd glip
mkdir build; cd build
../configure --enable-uart
sudo make install

Synthesize the design

Synthesize the example design with Xilinx Vivado.

cd GLIP_SOURCES/src/backend_uart/logic/demo/nexys4ddr
make vivado-project
vivado vivado/nexys4ddr.xpr

In vivado run the implementation and generate the bitstream.

Configure the FPGA

When the bitstream has been succesfully generated, open the Hardware Manager in Vivado, turn the board on and program the device.

Execute the loopback measurement tool

Execute the GLIP tool "Loopback Measure" that measures the loopback performance.

Before you start the measurement, make sure to set the DIP switches on Nexys 4 DDR board below the 7-segment display all to OFF, i.e. they all point towards the bottom of the PCB and away from the 7-segment display (this enables loopback mode). The 7-segment display should now display all zeros.

The design is set to 12 MBaud/s in the toplevel verilog file, we need to pass this speed to GLIP using the speed parameter. Run the loopback measurement tool like this:

glip_loopback_measure -b uart -ospeed=12000000,device=/dev/ttyUSB0

If the UART device cannot be found at /dev/ttyUSB0 try others like /dev/ttyUSB1 etc. If you can see the device, but cannot open, check the permissions.

The performance should be 1170 kByte/s bidirectional.