4-Bit ALU with TinyTapeout

This project implements a small 4-bit ALU in Verilog for TinyTapout. It supports arithmetic and logic operations and additionally contains an internal 8x4-bit register file to store values.

How it works

Inputs:

• ui_in[3:0] = A operand (4 bit)
• ui_in[7:4] = B operand (4 bit)
• uio[3:0] = opcode

Outputs:

• uo_out[3:0] = ALU result (4 bit)

• uo_out[4] = Carry flag

• uo_out[5] = Overflow flag

• uo_out[6] = Sign flag

• uo_out[7] = Zero flag

The ALU executes operations every clock cycle and the result is latched on rising edge of clk. There are two opcode ranges:

opcode (4 bit) Function 0000-0111 ALU core operations (ADD, SUB, AND, OR, XOR, SHIFT, PASS) 1xxx register read/write operations

The internal register file consists of 8 registers à 4 bit.

How to test

This ALU is easy to test with DIP switches:

1. set A on ui[3:0]
2. set B on ui[7:4]
3. choose opcode on uio[3:0]
4. read result and flags on uo[7:0]

Example: ADD 3 + 5

• A = 0011
• B = 0101
• opcode = 0000

result -> uo_out = 00001000

External hardware

No external hardware required. You can however attach LEDs for output and DIP switches for input. Lower 4 LEDs = result. Upper 4 LEDs = flags. Register file can be used to store values step-by-step to build tiny assembly-like programs.

Purpose

The goal is to demonstrate that TinyTapout can be used to build a small but fully functional CPU datapath element.