J-core j1 for Lattice ice40 FPGA, with GHDL build/test script

This is a stripped-down build of https://j-core.org j2 processor which is instruction set compatibile with the full j2 but has no I/O devices, DRAM controller or SMP support.

Install https://awesomeopensource.com/project/ghdl/ghdl and run ./ghdl_lattice.sh to build and simulate this CPU running a test rom. (If it prints the C0 line all instruction tests passed.) See the testrom/ directory for ROM source, for bare metal elf toolchain build instructions see: http://lists.j-core.org/pipermail/j-core/2019-October/000867.html

A working ICE40 UltraPlus5k bitstream was produced from this source via Lattice's Synplify+IceCube2 toolchain. It's also been tested with GHDL, NVC, Xilinx WebPack ISE, and Vivado.

We are working to get a fully open source VHDL toolchain (built from ghdl+ghdlsynth+yosys+abc) creating bitstreams from that (it doesn't yet). For build instructions for that see: http://lists.j-core.org/pipermail/j-core/2019-November/000868.html