Fully open source VHDL bitstream generator for iCE40 FPGA, built from
Yosys + GHDL + ghdlsynth + nextpnr + icestorm

  ./yogh.sh
  export PATH=~/yogh/bin:$PATH

Export PREFIX= to specify install location for new toolchain (default ~/yogh).
Export NONET=1 to skip git updates of subrepos (run without net access).
Export NOCLEAN=1 to skip repo clean (perform incremental build).

See script comments for build prerequisites (uses debian package names).