OPC: One Page CPUs
Welcome to the OPC series of CPUs, where everything fits on one page - one page each for specification, emulation, HDL. For details see the OPC Project web pages.
The OPCs range from OPC1 for CPLD to OPC6 for FPGA, which has been run successfully on several FPGA dev boards. For the OPC5, OPC6 and OPC7 there's also a C model for the PiTubeDirect project, which runs on a Pi as a second processor for an Acorn BBC micro.