I've always been interested in designing my own 8-bit CPU core in an FPGA for educational purposes. After visitingit seems the easiest/most popular way to go about this is to make the CPU core be compatible with an existing ISA (Instruction Set Architecture) from an available device (e.g. 8051, PIC, etc.). That way I could use readily available development tools to write code, debug, create a hex file, etc.
If by some chance I ever used my home grown, ISA compatible, core in a commercialized product, would there be legal issues? Chances are I would never use my own and would probably use a Nios or Microblaze instead, but if I just needed a simple little core, it could prove useful.
I know very little about the IP core business, but I've seen off the shelf compatible CPU cores for sale, so I'm guessing these IP companies must pay companies like Microchip when they sell a PIC compatible core?
Just curious if anyone has any insight into how all this works.