I also want to refer you to this http://fpgacpu.org/ http://fpgacpu.org/ especially the XSOC links. Jan builds a complete SoC-on-a-FPGA in really 'ancient' fab

I also want to refer you to this http://fpgacpu.org/ http://fpgacpu.org/ especially the XSOC links. Jan builds a complete SoC-on-a-FPGA in really 'ancient' fabric (4000-series Xilinx) for Circuit Cellar (articles available on this site). He also hacks a C compiler to emit code for his 16-bit RISC machine (which is very clever). This is historical, but a 'must read' if you're new to this stuff.