CPU32

A tiny MIPS implementation for Terasic DE0/DEx and other Altera FPGA boards

Demo

• Calculating Fibonacci numbers: video

Features

• Supports MIPS I instruction set with basic arithmetic ops, branches and other ops
• Runs MIPS I binary code generated from basic C program
• 32KB RAM (with Block RAM of Cyclone III)
• I/O: 7-seg LEDs for output, sw3 - sw0 for input
• Single clocked design (no pipeline)

Known Issues

• Does not support floating points, exceptions and etc
• No bus/cache/MMU support
• Consumes about 13k LEs, largely by dividers and multipliers generated by Quartus.
• May have some bugs :)

Getting Started

Prerequisites

• Terasic DE0/DEx or Altera FPGA development environment, including Altera Quartus II Web edition on Windows
• (Alternatively, you could use ModelSim for simulation only purpose)
• Experience of basic Altera FPGA development

Build

• Create a Quartus project named CPU32
• Copy /src and /conf folders under the project folder and add .v files to the project.
• Start Analysis & Elaboration for initial check. You would have errors on some .v files. Open property dialog and set language to "SystemVerilog" to resolve the errors
• Use Pin Planner for pin assignment of CPU32.v for clock, LEDs, switches and buttons
• Start Compilation for full build. This may takes several minutes

Run Fibonacci

• Use Programmer for loading to DE0
• You will see fibonacci numbers displayed on the LED

Run your own C code on CPU32

Cross-compile C code and generate binary on Linux

• Write your C code. You can not use system calls, exceptions, and floating point operations. If you like to use LED display or switchies, refer to the Memory Mappings section below
• Install mips-gcc on Linux. Add mips-gcc/bin directory to your PATH
• Install Python runtime
• Use c2mif.py to compile the .c file and generate .mif file

> python c2mif.py fib.c

Run the binary on CPU32

• Copy the mif file from the Linux to /conf folder in the Quartus project
• Edit bram.v file and replace "conf/fib.mif" with the path of your mif file
• Start Compilation on Quartus II and load it to the board

Memory Mappings and I/O access

Memory map

0x0000 ->        : text
       <- 0x7efc : stack
0x7f00 -- 0x7fff : global

          0x7f00 : to display a value on LED 
          0x7ff0 : to input params from sw3 - sw0

7-seg LED display modes

The 7-seg LED displays $7f00, PC or registers, based on switch setting:

sw9:   off = $7f00      on = PC or registers
sw8:   off = PC         on = reg
sw7:   off = low bytes  on = high bytes
sw6-5: not used
sw4-0: register address

License

• Apache License v2.0