Table of Contents

Getting started: Source code management

Vivado has "project mode" and "non-project mode". The project mode is typically used with the GUI and settings are kept in a project file. This is essentially the only mode described in Xilinx documentation and tutorials. Generally I prefer "non-project" mode, which is command-line or Makefile driven.

In either mode, I suggest to never run the tools in the directory containing the source tree, as Vivado clutters up the build directory with lots of temporary files.

Creating a project for project mode:

  $ source /opt/Xilinx/Vivado/2020.2/   # (change path as needed)
  $ vivado   # (opens the GUI)
  • Select "Create Project"
  • Select "Next".
  • Fill in a project name and directory (leave the "Create project subdirectory" checked). Select "Next"
  • Leave defaults: (RTL project, nothing else checked), Select "Next"
  • Leave defaults: Language "VHDL", simulator "mixed", select "Next"
  • No constraints: Select "Next"
  • Choose a part. "xc7a35tcpg236-1" for the Basys3 for example. Select "Next"
  • View summary, Select "Finish"

At this point I recommend to exit Vivado.

You'll see that Vivado has created a bunch of directories and files. I suggest to navigate to the top-level design directory (where the .xpr file sits and immediately create a directory called src to keep your source code and constraint files in.

Get or create a constraints file -- for Digilent boards you can get a master XDC file here (Github link). Edit it to uncomment the ports you are using. Recommend to save as top.xdc in your src folder.

Get or create a top-level VHDL source file -- Recommend to save as top.vhd in your src folder.

Attach files to project

  • Start vivado
  • Click "+" on "Sources" window or Alt-A, Select "Next"
  • Select "Add files", navigate to your file, select "Next"
  • Select "Finish"
  • Alt-A again, add your constraint file

Click the green "play" triangle and select "launch implementation" for a full build. This starts a build in the background, which will take several minutes for even a trivial example. You will observe that Vivado has now created a total of about 110 files and folders in your project directory, but the src folder should still have only your source and constraints files.

I recommend to store only the source (xpr) file, VHDL (.vhd) files and the project (.xpr) file in a repository at the start.

Quick simulation from command line

Create init.tcl and pulser.vhd

  xvhdl pulser.vhd
  xelab -debug typical pulser -s pulser_sim
  xsim --gui pulser_sim -t init.tcl

Omit the --gui and end the tcl script with quit to run in batch mode. Here is a simple example, to test a 4x4 multiplier with inputs (a,b) and output p:

puts "Starting multiplier test"
set errz 0
for {set i 0} {$i < 16} {incr i} {
    for {set j 0} {$j < 16} {incr j} {
	add_force a -radix dec $i
	add_force b -radix dec $j
	run 10
	set calc_p [expr {$i * $j}]
	set sim_p [get_value -radix unsigned p]
	if {$calc_p != $sim_p} {
	    puts "ERROR: Calculated: $calc_p simulated: $sim_p"
	    incr errz
puts "$errz total errors"

Building in Non-project Mode

Below is the simplest possible (?) build script for a Vivado project. Here is a fancier one from this blog fancy_build.tcl.

# create_project -force proj1 ./proj1
# read_vhdl proj1/src/top.vhd
# read_xdc proj1/src/pins.xdc
synth_design -top top -part xc7a12t-cpg238-1
write_bitstream -force proj1/proj1.bit

Here is a sample (working) constraints file with the minimum stuff in it:

set_property CFGBVS VCCO [current_design]
set_property CONFIG_VOLTAGE 2.5 [current_design]

set_property -dict { PACKAGE_PIN k17 IOSTANDARD LVCMOS25 } [get_ports clk]
set_property -dict { PACKAGE_PIN n19 IOSTANDARD LVCMOS25 } [get_ports rst]
set_property -dict { PACKAGE_PIN n17 IOSTANDARD LVCMOS25 } [get_ports a]
set_property -dict { PACKAGE_PIN p18 IOSTANDARD LVCMOS25 } [get_ports b]
set_property -dict { PACKAGE_PIN r19 IOSTANDARD LVCMOS25 } [get_ports y]

For completeness here is a minimal VHDL file which works with the above

library IEEE;
use IEEE.STD_LOGIC_1164.all;

entity top is
  port (
    clk  : in  std_logic;
    rst  : in  std_logic;
    a, b : in  std_logic;
    y    : out std_logic);

end entity top;

architecture arch of top is

begin  -- architecture arch

  process (clk, rst) is
  begin  -- process
    if rst = '0' then                   -- asynchronous reset (active low)
      y <= '0';
    elsif clk'event and clk = '1' then  -- rising clock edge
      y <= a and b;
    end if;
  end process;

end architecture arch;

Building With IP in Non-Project Mode

Got this from an AR, not tested/confirmed:

create_project -in_memory -part xc7vx415tffg1158-2
read_ip ./local_pcs_pma/local_pcs_pma.xci
set_property target_language VHDL [current_project]
generate_target all [get_files ./local_pcs_pma/local_pcs_pma.xci]
Last modified 18 months ago Last modified on Feb 12, 2021, 10:37:05 AM