Solved–Lab 1: Combinational Logic Design and Timing in Quartus– Solution

Description

Objectives:

1. Get familiar with Quartus Prime Lite Edition (v18.1, also select ModelSim and Cyclone V device support)
2. Understand the impact of combinational logic design on performance
3. Implement and verify a 1-bit adder (also called a full adder);
4. Use the full adder as a component to implement and verify the design of a 4-bit ripple-carry adder and 4-bit carry-save adder;

5. Compare the relative timing of the ripple-carry adder vs. the carry-save adder when many numbers are to be added together.

What to hand in:

1. The report attached at the end of this handout;
2. Demo to TA of your design

1. Introduction

In the term project arranged later in this semester, we will implement a MIPS-like processor from the scratch. This homework serves as a warm-up process that makes you familiar with the software design environment and the basic combinational logic design. Specifically, in this homework, you will implement multi-bit adders that are fundamental logic components in the ALU design.

Firstly, you need construct a 1-bit full adder first, and then implement an n-bit ripple-carry adder from full adders, and finally uses full adders to build a carry-save adder that is typically faster than the ripple-carry adder when many numbers are added together. Using the time analysis tool provided in Quartus, you are required to compare the relative performance of these two types of adders.

2. Background

1-bit adder: A 1-bit adder, as shown in the following figure, must have three inputs: two operands, and one
CarrayIn from the neighbor adder. There must be two outputs: a single-bit output for the sum and another single-bit output to pass on the carry, called CarryOut.

Figure 1. 1-bit adder

The truth table of a single-bit adder is given bellows.

* The author (Yifeng Zhu) gratefully acknowledges borrowing parts of this homework assignment from “UNL CSE 230 Computer Organization,” ©2005 by Dr. Sharad Seth.

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This truth table can be summarized by two logical equations

Sum = a Å b Å CarryIn

CarryOut = a × b + CarryIn × a + CarryIn × b

Multiple-bit ripple-carry adder. It is created by directly linking the carries of 1-bit adders, in which CarryOut of the less significant bit is connected to the CarryIn of the more significant bit. The following figure shows an example of a 4-bit ripple-carry adder that adds four 4-bit numbers: A, B, E, and F.

Figure 2. A 4-bit ripple-carry adder for four 4-bit numbers

Multiple-bit carry-save adder. It consists of multiple one-bit full adders, without any carry-chaining. Thus it can prevent time-consuming carry propagation and speed up computation. The following figure presents an example of a 4-bit carry-save adder that adds four 4-bit numbers: A, B, E, and F.

Figure 3. A 4-bit carry-save adder for four 4-bit numbers

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3. Implementation

1. Implement a 1-bit full adder

Figure 4. Implementation of a 1-bit full adder

(a) Draw the schematic of a single bit full adder, shown above in Quartus.

(b) Compile the design and verify the correctness with simulation.

(c) Create a default symbol for the single bit full adder. To create the default symbol, after compiling your design, select File from the main menu then select create/update, create symbol file for current file. A symbol will show in your current directory.

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2. Implement a 4-bit ripple carry adder

Figure 5. A 4-bit ripple-carry adder, where fa is short for “full adder”

(a) Draw the schematic shown above of the 4-bit ripple carry adder with Quartus. You need to use the full adder symbol created in problem 1. (You need to create a symbol file for the full adder that you have implemented previously (File → create/update → create symbol file for current file). Then, when you execute add symbol, you will find, in addition to the primitive symbols we already know, there is also the symbol you created! You could use it just like an ordinary symbol in your schematic.)

(b) Set appropriate value to a[3..0] and b[3..0] as well as cin to verify the design with simulation. (Hint: You do not need to exhaust all possible input combinations in truth table. But please use at least 5 combinations to verify your design.)

(c) Create a default symbol for the 4-bit ripple carry adder.

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3. Implement a ripple-carry adder for four 4-bit numbers

Figure 6. Implementation of a 4-bit ripple-carry adder for four 4-bit numbers

(a) Draw the schematic of the ripple carry addition of four 4-bit numbers with Quartus. You need to use the full adder symbol and the 4-bit ripple carry adder symbol created previously.

(b) Compile the design.

(c) Choose the following set of values for a, b, e, f to verify the design with simulation.

• 15+1+14+5=35

• 12+11+3+1=27

• 15+15+15+15=60

• 7+9+12+15=43

• 3+11+19+4=37

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4. Implement a 4-bit carry-save adder

Figure 7. Implementation of a 4-bit carry-save adder

(a) Draw the schematic of a 4-bit carry-save adder in Quartus. You need to use the full adder symbol created previously.

(b) Compile the design.

(c) Create a symbol for the 4-bit carry –save adder

(d) Choose the following set of values for a, b, f to verify the design with simulation.

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5. Implement a 4-bit carry-save adder for four 4-bit numbers

(a) Implement a carry-save adder of four 4-bit numbers by using the 4-bit carry-save adder, 4-bit ripple-carry adder, and/or the full adder that you have implemented previously.

(b) Compile the design.

(c) Choose the following set of values for a, b, e, f to verify the design with simulation.

• 15+1+14+5=35

• 12+11+3+1=27

• 15+15+15+15=60

• 7+9+12+15=43

• 3+11+19+4=37

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Appendix 1: Installation of Quartus

(The following instructions are copied from the website of atlera.com.)

1. Download the free Quartus Prime Software Lite Edition (Version 17.0) from Altera’s website ( https://www.altera.com/downloads/download-center.html )
2. Be aware that the install file is large and it takes time to download.
3. Install the USB-Blaster driver. After connecting the board to the computer via USB, the following warning message may appear. Go to “Control Panel” → “Hardware and Sound” → “Device Manager”, double-click the entry labeled USB-Blaster, right-click, update the driver. The driver is in the directory:

C:\intelFPGA_lite\17.0\quartus\drivers\usb-blaster

Appendix 2: Tips on Simulation, Waveform Editing

Quartus provides a built-in simulator (University Program Simulation Tool) to verify the correctness of a logic circuit. This tool is intended for students who are taking a course in logic circuit design. Before simulating a project, we must compile it successfully.

1. To create a new waveform window, use “File → New → University Program VWF” to create a simulation waveform file
2. To insert a node (a waveform), RIGHT CLICK and do Insert Node. If your waveform editor file is named the same as the graphic file, then you can use the ‘List’ button to list all available nodes and choose one.
3. To change the value of portion of the waveform, click and drag on the portion of the waveform to change – then click on either the ‘1’ or ‘0’ button along the left-hand side to change this portion to a 1 or 0.
4. To set the END TIME of the simulation waveform, make sure the waveform window is selected, and then use Edit → End Time to set the ending time.

5. To insert a clock waveform, select the signal, RIGHT CLICK, choose value and then clock.

6. Output signals like DOUT do not have to be edited by you. But you must add these nodes into the waveform window to monitor the output. Their values will be updated when you run the simulator.

7. Start simulation. In the waveform editor, click the menu SIMULATION to perform either function simulation or timing simulation.

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Appendix 3: Tutorial of Creating a Busline in Quartus

In this tutorial, we illustrate how to create a busline for the component 8dffe (8-bit D-Flip-flop).

Step 1: Create a new project.

• Select the device 5CEBA4F23C7 in the Cyclone V family.

Step 2: Create Block Diagram

• Follow menu: File → New → Select “Block Diagram/Schematic File”

• Insert two components: 8dffe and input

• Rename an Input

o Method 1: Double click on “pin_name” and rename it to “myinput[7..0]”, or
o Method 2: Right-click the input component, and then rename it in the pop-up window.

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Notice, we name the bus myinput[7..0]. This means it is an 8 bit bus where the least significant bit is bit

0. Make sure you use this convention with every component. Failure to do so can cause a lot of headaches.

• Create a Busline: Extend a Busline from the INPUT by using Orthogonal Bus Tool

• Connect the busline with 8dffe

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• Rename Each Line: Right-click to name the bus lines, select Properties to change/add the name. The line myinput[0] is the least significant bit.

Tips:

1. We don’t need wires connecting everything if they have the same name.
2. We can concatenate two bus lines to form a new one. For example, a busline named as
A[7..3],B[2..0] will form a new bus line that takes the most significant five bits of Bus A and the least significant three bits of Bus B to four a new 8-bit bus.

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Report of Lab 1

Combinational Logic Design and Timing

Name: ______________________________

Demo of design to TA (40 points)

Time analysis of ripple-carry adders and carry-save adders (10 points)

Assume the propagation delay of the AND/OR gate is 1 time unit, the propagation delay of the XOR is 2 time units, ignore the delays in the wires and connections and answer the following questions.

1. What is the delay in a 1-bit full adder in Figure 4?

2. What is the delay in a 4-bit ripple carry adder in Figure 5?

3. What is the delay in the ripple carry addition of four 4-bit numbers in Figure 6?

4. What is the delay in a 4-bit carry-save adder in Figure 7?

5. What is the delay in the carry-save adder of four 4-bit numbers?

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