1.3.2. Programming the FPGA

After the installation of Vivado, we will have to clone the FPGA repository and edit an existing project for our “Hello World” (Blink) project.

1.3.2.1. Clone FPGA GitHub repository

Go to the Red Pitaya FPGA Github site and download the ZIP folder of this project.

If you are using Windows, download the project repository and extract it to a folder of your choice. Remember the path to the location of the extracted repository (when you will be searching for your disk location in the WSL, go to the root directory and move into the mnt directory).

Alternatively, if you are using Linux or WSL, you can first install git, then move to a desired location and make a clone of the Red Pitaya Git repository:

sudo apt-get install git
git clone https://github.com/RedPitaya/RedPitaya-FPGA.git

1.3.2.2. Make an FPGA project

Go to the downloaded Red Pitaya FPGA Repository ZIP location and extract it to a folder/directory on your computer.

LinuxWindows

Open Vivado and using the TCL console navigate to the extracted folder and make a Vivado project.

. /opt/Xilinx/Vivado/2020.1/settings64.sh
cd Downloads/
cd RedPitaya-FPGA/
make project PRJ=v0.94 MODEL=Z10

Note

The instructions above are an example for how to create an empty v0.94 project for STEMlab 125-14. For other boards, please use the flags in the table below. For more information on alternative Project flag options options, please refer to Developers Guide Software.

Table of required build flags for the recommended v0.94 FPGA project per board:

Model	Build Project flag	Build Model flag
STEMlab 125-10 STEMlab 125-14	PRJ=v0.94	MODEL=Z10
STEMlab 125-14-Z7020	PRJ=v0.94	MODEL=Z20_14
SDRlab 122-16	PRJ=v0.94	MODEL=Z20
SIGNALlab 250-12	PRJ=v0.94_250	MODEL=Z20_250
STEMlab 125-14 4Ch Z7020	PRJ=v0.94	MODEL=Z20_125_4CH

For this project, you will only have to edit the red_pitaya_top.sv file. Edit the port led_o assignment at the beginning of the file. Change the port to output logic.

Now, in this section of the file, comment out the led_o port.

Finally, insert this code at the end of the module, before endmodule: red_pitaya_top. It will make the LED blink.

reg [27:0]counter = 28'd0;
reg led = 1'b0;
always @ (posedge adc_clk) begin
    counter = counter+1;
    if (counter == 28'd256000000) begin      // 256e6 periods of clock of 125 MHz
        led = ~led;                          // led will blink with a period of aprox. 2 sec
        counter = 28'd0;                     // reset the counter
    end
end
assign led_o[0] = led;                       // assign the register value to the led output

Now you have to start synthesis, implementation, and writing a bitstream. Press the button to start the synthesis. You can also just click on the “Generate bitstream” and all the steps will execute automatically.

After synthesis is finished, start implementation.

Implementation finished. Start writing the bitstream.

The bitstream file red_pitaya_top.bit is located in …/prj/v0.94/project/repitaya.runs/impl_1

You have to send this file to your Red Pitaya board. Open a terminal and connect to your Red Pitaya using an SSH connection. Also, enable the read/write operation on the Red Pitaya. To establish the connection you can either use your Red Pitaya’s IP address or the “rp-xxxxxx.local”, where “xxxxxx” are the last six characters of the MAC address.

ssh root@rp-xxxxxx.local
redpitaya> rw

1.3.2.2.1. Reprogramming the FPGA

How the FPGA is reprogrammed depends on the Red Pitaya OS version.

Please make sure that the PATH environment variable is set correctly. See Vivado installation guide for more information.

Note

On Windows, the easiest way is to perform the process inside Vivado’s TCL console. The process can also be done through a standard Command Prompt, but any echo commands must be executed inside the Windows Subsystem for Linux (WSL) Terminal (The output file encoding is a problem with Windows echo). For more information, refer to the following forum topics:

• ́╗┐' is not recognized as an internal or external command

• Diagnosing why your batch file prints a garbage character, one character, and nothing more

OS version 1.04 or olderOS version 2.00

Please note that you need to change the forward slashes to backward slashes on Windows.

1. Open Terminal or CMD and go to the .bit file location.

cd <Path/to/RedPitaya/repository>/prj/v0.94/project/repitaya.runs/impl_1

2. Send the file .bit (red_pitaya_top.bit is the default name) to the Red Pitaya with the scp command.

scp red_pitaya_top.bit root@rp-xxxxxx.local:/root

3. Now establish an SSH communication with your Red Pitaya and check if you have the copy red_pitaya_top.bit in the root directory.

redpitaya> ls

4. Load the red_pitaya_top.bit to xdevcfg with

redpitaya> cat red_pitaya_top.bit > /dev/xdevcfg

After executing the last command, you should see an LED blink. Congratualtions on writing your first FPGA program!

1.3.2.2.2. Reverting to original FPGA image

If you want to roll back to the official Red Pitaya FPGA program, run the following command:

OS version 1.04 or olderOS version 2.00

redpitaya> cat /opt/redpitaya/fpga/fpga_0.94.bit > /dev/xdevcfg

or simply restart your Red Pitaya.