Lab 2: Single-Cycle CPU (Simple Version) Solution

    1. Goal

Utilizing the ALU in Lab1 to implement a simple single cycle CPU. CPU is the most important unit in computer system. Read the document carefully and do the Lab, and you will have the elementary knowledge of CPU.

    2. Requirement

        (1) Please use Xilinx ISE as your HDL simulator.

        (2) Please attach your names and student IDs as comment at the top of each file.

        (3) Please use the Program Counter, Instruction Memory, Register File and Test Bench we provide you.

        (4) Instruction set: the following instructions are to run on your CPU (60 pts.).




Instruction
Example


Meaning
Opcode

Function


Add unsigned
addu r1, r2, r3

r1
= r2 + r3
000 000

100 001












Add
addi r1, r2, 100

r1
= r2 +100
001 000

-


immediate





























Subtract
subu r1, r2, r3

r1
= r2 - r3
000 000

100 011


unsigned





























Bitwise and
and r1, r2, r3

r1
= r2 & r3
000 000

100 100












Bitwise or
or r1, r2, r3

r1
= r2 | r3
000 000

100 101











Set on
slt r1, r2, r3

if(r2 < r3)





less than



r1 = 1
000 000

101 010





else


















r1 = 0














Set on
sltiu r1, r2, 10

if(r2 < 10)





less than



r1 = 1
001 011

-


immediate


else














unsigned



r1 = 0














Branch
beq r1, r2, 25

if(r1 == r2)
000 100

-


on equal



PC += (25 << 2)
























Computer Organization, Spring, 2018


    3. Architecture Diagram


































    4. Advance Instructions (20 pts.)

Modify the architecture of the basic design above.

        (1) ALUOp should be extended to 3bits to implement I-type instructions. Original 2bits ALUOp from textbook : 00 -> 000, 01 -> 001, 10 -> 010.
        (2) Encode shift right and LUI instruction by using unused ALU_ctrl.

Ex. ALU_ctrl = 0 is AND, 1 is OR..., 0 1 2 6 7 &12 are used by basic instructions.


Instruction
Example

Meaning
Opcode

Function


Shift right
sra r1, r2, 10
r1
= r2 >> 10
000 000

000 011


arithmetic


























Shift right
srav r1, r2, r3
r1
= r2 >> r3





arithmetic



000 000

000 111


variable

















Load upper
lui r1, 10
r1
=10<<16
001 111

-


immediate


























Or immediate
ori r1, r2, 100
r1
= r2 | 100
001 101

-










Branch on not
bne r1, r2, 30
if(r1 != r2)
000 101

-


equal


PC += (30 << 2)






















Computer Organization, Spring, 2018


To implement those advanced instructions, please note about the following formats.

SRA Rd, Rt, shamt

0
-
Rt
Rd
shamt
3






6
5
5
5
5
6

Shift register Rt right arithmetically by the distance indicated by immediate shamt. Rs is ignored for sra.

SRAV Rd, Rt, Rs

0
Rs
Rt
Rd
0
7






6
5
5
5
5
6

Shift register Rt right arithmetically by the distance indicated by the register Rs. Hint: Be careful of using Verilog operator >>> directly in your code. To use this operator, you have to declare the variable as signed.

LUI Rt, Imm

0xf
0
Rt
Imm




6
5
5
16

Load the lower halfword of the immediate imm into the upper halfword of register Rt. The lower bits of the register are set to 0.

ORI Rt, Rs, Imm

0xd
Rs
Rt
Imm




6
5
5
16

Put the logical OR of register Rs and the zero-extended immediate into register Rt.

    5. Test

There are 3 test patterns, CO_P2_test_data1.txt ~ CO_P2_test_data3.txt. The default pattern is the first one. Please change the column 39 in the file "Instr_Memory.v" if you want to test the other cases.

column 39 : $readmemb("CO_P2_test_data1.txt", Instr_Mem) The following are the assembly code for the test patterns.

1
2
3
addi r1,r0,13
addi r6,r0,-2
ori r10,r0,3
addi r2,r0,7
addi r7,r0,5
lui r11,-10



Computer Organization, Spring, 2018


sltiu r3,r1,0xFFFF

or r8,r6,r7

sra r11,r11,8

beq r3,r0,1

addi r9,r0,-1

srav r11,r11,r10

slt r4,r2,r1

addi r6,r6,2

addi r10,r10,-1

and r5,r1,r4

addu r9,r9,r6

bne r10,r0,-3

subu r4,r1,r5

beq r6,r0,-3









final result

final result

final result

r1 = 13, r2 = 7, r3 = 1,

r6 = 2, r7 = 5,

r10 = 0, r11 = -40

r4 = 12, r5 = 1

r8 = -1, r9 = 1
















The file "CO_P2_Result.txt" will be generated after executing the Testbench. Check your answer with it.

    6. Grade

        (1) Total score: 100 pts. COPY WILL GET A 0 POINT!

        (2) Basic score: 60 pts. Advance instructions: 20 pts.

        (3) Report: 20 pts – format is in CO_Report.docx.

        (4) Delay: 10 pts off per day

    7. Hand in your assignment

        (1) Zip your folder and name it as "ID1_ID2.zip" (e.g., 0516001_0516002.zip) before uploading to e3. Other filenames and formats such as *.rar and *.7z are NOT accepted! Multiple submissions are accepted, and the version with the latest time stamp will be graded.

        (2) Please include ONLY Verilog source codes (*.v) and your report (*.docx or *.pdf) in the zipped folder. There will be many files generated by the simulation tool (Xilinx) - do not include them; WE NEED ONLY VERILOG SOURCE CODES AND YOUR REPORT!

    8. Q&A

For any questions regarding Lab 2, please contact 曾威凱 (k50402k@gmail.com) and 周煥然 (kulugu2@gmail.com).

    9. Appendix

You can use 32bits ALU to do this lab.

Here is the example of 32bits ALU from textbook.
Computer Organization, Spring, 2018