MPX

Github: https://github.com/ultraembedded/core_mpx

MPX is an open-source CPU which can execute code compiled for MIPS-I ISA (as per the MIPS R2000 / R3000 CPUs).

Disclaimer: I am not associated with MIPs Technologies Inc.
The version of MIPS ISA implemented here is 30+ years old, so undoubtedly any patents related to it will have expired.
This core was implemented using only publically available ISA documentation.

This core is not a good starting point for new designs. You should consider using RISC-V based designs instead, as RISC-V is a cleaned up and more modern RISC ISA that is also open-source.

I have designed multiple RISC-V cores that you should consider instead of MPX;

• https://github.com/ultraembedded/biriscv
• https://github.com/ultraembedded/riscv

Rationale

So why design this core? Well... There are some interesting real-world products that featured MIPS R3000 CPUs such as the Sony Playstation 1, and there are ongoing efforts to recreate them in modern FPGA technology.

Overview

Features

• 32-bit MIPS-I ISA compatible CPU core.
• Simple 5-stage pipelined design.
• Support for external co-processors (COP1 - 3).
• Synthesizable Verilog 2001, Verilator and FPGA friendly.

Note: This core does not have a built-in floating-point unit (COP1), however, one can be implemented and connected to the top-level ports of the design.

Status

This is a very early release of the RTL. There are likely to be bugs!

Known items on the TODO list are;

• Implement faults on invalid instructions (RI) and arithmetic overflow (OV).
• Optimise the instruction decoder to be smaller and have a shorter critical path.
• Re-implement various bugs and quirks found in actual MIPS R2000/3000 designs.
• Rework multiply/divide instructions to be non-blocking (the current implementation is faster than the original but blocking).
• Rework the co-processor interfaces to reduce the CPU critical path.
• More extensive verification is required.