nextpnr

nextpnr is an open-source, portable FPGA place-and-route tool designed to provide a common P&R backend for multiple FPGA architectures. It focuses on being architecture-agnostic, with device-specific backends implementing the wiring and timing constraints needed to place and route a design on a particular FPGA family.

The typical workflow uses a synthesis tool such as Yosys to produce a netlist, which is then converted into a device-independent JSON description that, along with a device database and user constraints, is consumed by nextpnr. The tool performs placement and routing and emits a routed design in a format suitable for a vendor’s bitstream tool. Users typically run nextpnr as part of an open-source toolchain to derive a final bitstream.

Backends and architectures: nextpnr includes backends for multiple FPGA families, notably the Lattice iCE40 and the Lattice ECP5, with architecture data and routing models implemented for each device. New devices can be supported by adding an architecture description and backend code. The iCE40 backend is widely used in open-source flows such as IceStorm, while the ECP5 backend is used in Trellis-based pipelines; the project also integrates with broader open-source ecosystems such as SymbiFlow.

Usage: A typical flow is to synthesize with Yosys, generate a JSON netlist, run nextpnr with the appropriate backend (for example nextpnr-ice40 or nextpnr-ecp5) to produce a routed design, and then use a vendor tool (such as icepack for iCE40 or ecppack for ECP5) to generate a final bitstream. Command-line options specify the target device, constraints, and timing objectives.

Development and community: nextpnr is an active, community-driven project under open-source licenses. It attracts contributors from hobbyist, academic, and industrial communities and is used in educational open hardware platforms and research projects to explore FPGA architectures and open toolchains.