A Free and Open Source Verilog-to-Bitstream Flow for iCE40 FPGAs
Yosys (Yosys Open Synthesis Suite) is an Open Source Verilog synthesis and verification tool.
Project IceStorm aims at reverse engineering and documenting the bit-stream format of Lattice iCE40 FPGAs and providing simple tools for analyzing and creating bit-stream files, including a tool that converts iCE40 bit-stream files into behavioral Verilog. Currently the bitstream format for iCE40 HX1K and HX8K is fully documented and supported by the tools.
Arachne-PNR is an Open Source place&route tool for iCE40 FPGAs based on the databases provided by Project IceStorm. It converts BLIF files into an ASCII file format that can be turned into a bit-stream by IceStorm tools.
This three projects together implement a complete open source tool-chain for iCE40 FPGAs. It is available now and it is feature complete (with the exception of timing analysis, which is work in progress).