Description
Problem 1 [5 points] Design a 16-bit barrel shifter in Verilog with the following interface. If you need additional information on barrel shifter design, you can consult the ALU lecture notes. Inputs: • [15:0] In – 16-bit input operand value to be shifted • [3:0] Cnt – 4-bit amount to shift (number of bit positions to shift) • [1:0] Op – shift type, see encoding in table below Output: • [15:0] Out – 16-bit output operand Opcode Operation 00 Rotate left 01 Shift left 10 Shift right arithmetic 11 Shift right logical (Aside: you should think about if the above 4 opcodes are sufficient to represent all of the shift operations you need to implement for your project.) Before starting to write any Verilog, you should do the following: 1. Break down your design into sub-modules. 2. Define interfaces between these modules. 3. Draw paper and pencil schematics for these modules (these will be handed in as scanned schematic.pdf file). 4. Then start writing Verilog. Verify the design using the testbench in the supplied tar file and on Github Classroom. For a simple walkthrough of how to run the testbench and example outputs see the Homework 4 Demo page. Problem 2 [10 points] This problem should also be done in Verilog. Design a simple 16-bit ALU. Operations to be performed are 2’s Complement ADD, bitwise-OR, bitwise-XOR, bitwise-AND, and the barrel shifter unit from problem 1. Additionally, it must have the ability to invert either of its data inputs before performing the operation and have a Cin input (to enable subtraction). Another input line also determines whether the arithmetic to be performed is signed or unsigned. Use a ripple carry adder (e.g., from homework 3) in your design. For all the shift and rotate operations, assume the number to shift is input A to ALU and the shift/rotate amount is bits [3:0] of input B. Opcode Function Result 000 rll Rotate left 001 sll Shift left logical 010 sra Shift right arithmetic 011 srl Shift right logical 100 ADD A+B 101 AND A AND B 110 OR A OR B 111 XOR A XOR B The external interface of the ALU should be: Inputs • A[15:0], B[15:0] – Data input lines A and B (16 bits each). • Cin – A carry-in for the LSB of the adder. • Op(2:0) – The OP code (3 bits). The OP code determines the operation to be performed. The opcodes are shown in the Table above. • invA – An invert-A input that causes the A input to be inverted before the operation is performed. invA is active high, which means it inverts A when invA is 1. • invB – An invert-B input (also active high) that causes the B input to be inverted before the operation is performed. • sign – A signed-or-unsigned input (active high for signed) that indicates whether signed or unsigned arithmetic to be performed for ADD function on the data lines (this affects the Ofl output). Outputs • Out(15:0) – Output data from your ALU (16 bits). • Ofl – (1 bit) This indicates high if an overflow occurred. • Zero – (1 bit) This indicates that the result is exactly zero. Other assumptions: • You can assume 2’s complement numbers. • In case of logic functions, Ofl is not asserted (i.e. kept logic low). The top-level module definitions and a testbench is included in the supplied tar file (on Canvas) and on Github Classroom. You must not change these top-level module names. Simulate and verify your design using the supplied testbench or create one yourself to test any of your submodules. You must reuse the barrel shifter unit designed in Problem 1. As in problem 1, before starting to write any Verilog, you should do the following: 1. Break down your design into sub-modules. 2. Define interfaces between these modules. 3. Draw paper and pencil schematics for these modules (these will be handed in as schematic.pdf file). 4. Then start writing Verilog.
