nextpnr -- a portable FPGA place and route tool

nextpnr is an FPGA place and route tool with emphasis on supporting timing-driven place and route for a wide range of real-world FPGA devices. It currently supports Lattice iCE40 devices and Lattice ECP5 devices, as well as a "generic" back-end for user-defined architectures. (ECP5 and "generic" support are still experimental.)

Currently nextpnr is beta software at best. But we aim at replacing arachne-pnr as official place-and-route tool for the icestorm flow soon.

Here is a screenshot of nextpnr for iCE40. Build instructions and getting started notes can be found below.

Prerequisites

The following packages need to be installed for building nextpnr, independent of the selected architecture:

• CMake 3.3 or later
• Modern C++11 compiler (clang-format required for development)
• Qt5 or later (qt5-default for Ubuntu 16.04)
• Python 3.5 or later, including development libraries (python3-dev for Ubuntu)
  • on Windows make sure to install same version as supported by vcpkg
• Boost libraries (libboost-dev or libboost-all-dev for Ubuntu)
• Latest git Yosys is required to synthesise the demo design
• For building on Windows with MSVC, usage of vcpkg is advised for dependency installation.
  • For 32 bit builds: vcpkg install boost-filesystem boost-program-options boost-thread boost-python qt5-base
  • For 64 bit builds: vcpkg install boost-filesystem:x64-windows boost-program-options:x64-windows boost-thread:x64-windows boost-python:x64-windows qt5-base:x64-windows
• For building on macOS, brew utility is needed.
  • Install all needed packages brew install cmake python boost boost-python3 qt5
  • Do not forget to add qt5 in path as well echo 'export PATH="/usr/local/opt/qt/bin:$PATH"' >> ~/.bash_profile

Getting started

nextpnr-ice40

To build the iCE40 version of nextpnr, install icestorm with chipdbs installed in /usr/local/share/icebox. Then build and install nextpnr-ice40 using the following commands:

cmake -DARCH=ice40 .
make -j$(nproc)
sudo make install

A simple example that runs on the iCEstick dev board can be found in ice40/blinky.*. Usage example:

cd ice40
yosys -p 'synth_ice40 -top blinky -json blinky.json' blinky.v               # synthesize into blinky.json
nextpnr-ice40 --hx1k --json blinky.json --pcf blinky.pcf --asc blinky.asc   # run place and route
icepack blinky.asc blinky.bin                                               # generate binary bitstream file
iceprog blinky.bin                                                          # upload design to iCEstick

Running nextpnr in GUI mode:

nextpnr-ice40 --json blinky.json --pcf blinky.pcf --asc blinky.asc --gui

(Use the toolbar buttons or the Python command console to perform actions such as pack, place, route, and write output files.)

nextpnr-ecp5

For ECP5 support, you must download Project Trellis, then follow its instructions to download the latest database and build libtrellis.

cmake -DARCH=ecp5 .
make -j$(nproc)
sudo make install

• For an ECP5 blinky, first synthesise using yosys blinky.ys in ecp5/synth.

• Then run ECP5 place-and route using ./nextpnr-ecp5 --json ecp5/synth/blinky.json --basecfg ecp5/synth/ulx3s_empty.config --bit ecp5/synth/ulx3s.bit

• Note that ulx3s_empty.config contains fixed/unknown bits to be copied to the output bitstream

• You can also use --textcfg out.config to write a text file describing the bitstream for debugging

• More examples of the ECP5 flow for a range of boards can be found in the Project Trellis Examples.

• Currently the ECP5 flow supports LUTs, flipflops and IO. IO must be instantiated using TRELLIS_IO primitives and constraints specified using LOC and IO_TYPE attributes on those instances, as is used in the examples.

nextpnr-generic

The generic target allows to run place and route for an arbitrary custom architecture.

cmake -DARCH=generic .
make -j$(nproc)
sudo make install

TBD: Getting started example for generic target.

Additional notes for building nextpnr

Use cmake -D options to specify which version of nextpnr you want to build.

Use -DARCH=... to set the architecture. It is semicolon separated list. Use cmake . -DARCH=all to build all supported architectures.

The following runs a debug build of the iCE40 architecture without GUI and without Python support and only HX1K support:

cmake -DARCH=ice40 -DCMAKE_BUILD_TYPE=Debug -DBUILD_PYTHON=OFF -DBUILD_GUI=OFF -DICE40_HX1K_ONLY=1 .
make -j$(nproc)

Notes for developers

• All code is formatted using clang-format according to the style rules in .clang-format (LLVM based with increased indent widths and brace wraps after classes).
• To automatically format all source code, run make clangformat.
• See the wiki for additional documentation on the architecture API.

Testing

• To build test binaries as well, use -DBUILD_TESTS=ON and after make run make tests to run them, or you can run separate binaries.
• To use code sanitizers use the cmake options:
  • -DSANITIZE_ADDRESS=ON
  • -DSANITIZE_MEMORY=ON -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
  • -DSANITIZE_THREAD=ON
  • -DSANITIZE_UNDEFINED=ON
• Running valgrind example valgrind --leak-check=yes --tool=memcheck ./nextpnr-ice40 --json ice40/blinky.json

Links and references

Synthesis, simulation, and logic optimization

• Yosys
• Icarus Verilog
• ABC

FPGA bitstream documentation (and tools) projects

• Project IceStorm (Lattice iCE40)
• Project Trellis (Lattice ECP5)
• Project X-Ray (Xilinx 7-Series)
• Project Chibi (Intel MAX-V)

Other FOSS FPGA place and route projects

• Arachne PNR
• VPR/VTR
• SymbiFlow
• Gaffe
• KinglerPAR