Building a 16-bit CPU from Scratch on FPGA (nand2tetris)

• Some may ask how many lines of code are required to design a simple programmable CPU?

• The answer is less than 350 lines of verilog code.

Starting from a single Nand gate, you'll build a 16-bit blinky CPU that runs on real-world FPGAs.

Prerequisites

A small laptop is enough for this project. No extra hardware required.

Software to be installed:

• Make
• iverilog
• gtkwave

If you'd like to run this CPU on real FPGAs, here's the synthesis report in Lattice Diamond:

Design Summary
   Number of registers:    152 out of  4635 (3%)
      PFU registers:          152 out of  4320 (4%)
      PIO registers:            0 out of   315 (0%)
   Number of SLICEs:       134 out of  2160 (6%)
      SLICEs as Logic/ROM:    134 out of  2160 (6%)
      SLICEs as RAM:            0 out of  1620 (0%)
      SLICEs as Carry:         10 out of  2160 (0%)
   Number of LUT4s:        267 out of  4320 (6%)
      Number used as logic LUTs:        247
      Number used as distributed RAM:     0
      Number used as ripple logic:       20
      Number used as shift registers:     0
   Number of PIO sites used: 5 + 4(JTAG) out of 105 (9%)
   Number of block RAMs:  4 out of 10 (40%)
   Number of GSRs:        0 out of 1 (0%)

It's so tiny that virtually any randomly chosen FPGA should work.

Instructions

Detailed instructions will be given under each directory.

Step 1 - Environment Setup

Build useful gates starting from a single Nand gate.

• Nand.v
• Not.v
• And.v
• Or.v
• Xor.v

Step 2 - ALU

Time to build an ALU.

• Mux.v
• Not16.v
• And16.v
• Mux16.v
• Or8Way.v
• HalfAdder.v
• FullAdder.v
• Add16.v
• ALU.v

Step 3 - CPU

A working 16-bit CPU:

• CPU.v

Step 4 - Computer

A programmable computer with input (buttons) and output (LEDs):

• Reset.v
• Memory.v
• Rom.v
• Hack.v

Related Projects

• https://www.nand2tetris.org/
• https://gitlab.com/x653/nand2tetris-fpga/
• https://github.com/theapi/nand2tetris_fpga