Getting Started with SymbiFlow Toolchain development


This documentation explains the first steps in the development of the toolchain itself. If you are looking for the user documentation, please look at instead.

This section provides an introduction on how to get started with the development of the SymbiFlow toolchain. In order to generate a bitstream (or any intermediate file format), you can use one of the toolchain tests. The following steps describe the whole process:

Clone repository

git clone

Prepare environment

Download all the necessary packages, tools and databases into an isolated conda environment:

cd symbiflow-arch-defs
make env

This also checks out all the submodules and generates the build system (Make or Ninja) from the CMake configuration. If you want to use the Ninja build tool add this line before calling make env:

export CMAKE_FLAGS="-GNinja"

Build example

While different architectures provide different build targets, there are some targets that should exist for all architectures.

Each architecture has its own toolchain backend that will be called during build. (See Project X-Ray and Project Trellis for more information)

For development purposes a set of test designs are included for each supported architecture. In order to perform a build of a test design with the Make build system enter the appropriate test build directory specific to your target architecture and invoke desired make target. Assuming that you would like to generate the bitstream .bit file with the counter example for the Arty board, which uses Xilinx Artix-7 FPGA, you will execute the following:

cd build/xc/xc7/tests/counter
make counter_arty_bit

If you use Ninja then the target is accessible from root build directory:

cd build
ninja counter_arty_bit


Test design targets names are based on the following naming convention: <design>_<platform>_<target_step>, where <target_step> is the actual step to be done, e.g.: bit, place, route, prog.


Generating architecture files is expected to take a long time to build, even on fast machines.

Load bitstream

The last step is to load the bitstream to your platform. The final output file can be found in the appropriate test directory, i.e: build/xc/xc7/tests/counter/counter_arty/artix7-xc7a50t-arty-swbut-roi-virt-xc7a50t-arty-swbut-test/top.bit

For every board the loading process may be different and different tools will be required. OpenOCD is the most widely used tool for loading bitstream in the Symbiflow Toolchain. It is provided as a conda package during the environment setup and CMake keeps track of its executable. Other programming tools used in Symbiflow that are automatically downloaded and referenced by CMake are tinyfpgab and tinyprog.

For convenience the prog targets are provided for loading the bitstream, e.g.:

make counter_arty_prog

or for Ninja:

ninja counter_arty_prog


Loading the bitstream into an FPGA can be done outside of the Symbiflow. There are multiple tools for loading bitstreams into FPGA development boards. Typically, each tool supports a specific target family or the lines of products of a vendor. Some of the most known are listed in hdl/constraints/prog


OpenFPGALoader is an universal utility for programming the FPGA devices that is a great alternative to OpenOCD. It supports many different boards with FPGAs based on the architectures including xc7, ECP5, iCE40 and many more. It can utilize a variety of the programming adapters based on JTAG, DAP interface, ORBTrace, DFU and FTDI chips.

Installing OpenFPGALoader

OpenFPGALoader is available in several packaging solutions. It can be installed with distribution specific package managers on Arch Linux and Fedora. There are also prebuilt packages available in conda or packages in tool repository. OpenFPGALoader can also be built from sources. For installation guidelines using both prebuilt packages and building from source please refer to instructions in readme.


For programming the FPGA use one of these commands:

openFPGALoader -b <board> <bitstream>           # (e.g. arty)
openFPGALoader -c <cable> <bitstream>           # (e.g. digilent)
openFPGALoader -d <device> <bitstream>          # (e.g. /dev/ttyUSB0)

You can also list the supported boards, cables and fpgas:

openFPGALoader --list-boards
openFPGALoader --list-cables
openFPGALoader --list-fpga

If you encounter any issues, please refer to the OpenFPGALoader README as it provides more useful information on the usage of the tool.