Single Cycle CPU

1
Single Cycle CPU
Chris Nevison, Colgate University (with minor
modifications by Alyce Brady, Kalamazoo College)
2
Read Select
M U X
Data Out
M U X
Data Out
Register File Read 2 Registers Simultaneously
3
Read Select
M U X
D E C O D E R
Data Out
Write Select
M U X
Data Out
Write Enable
Clock
Data In
Register File Read 2 and Write 1 Simultaneously
4
Write?
Registers
Select Register
Data Output
Data Input
One Step Back
5
Write?
Which op.
Registers
Select
R-Type Instruction Path e.g., add t0, t1, t2
6
Write
Registers
Mem Read
Select
Data Memory
0 1
M U X
1 0
M U X
Sign Ext
Mem Write
Immediate
R-Type Instruction Path (in a larger
context) e.g., add t0, t1, t2
7
Write
Registers
Mem Read
Select
Data Memory
0 1
M U X
1 0
M U X
Sign Ext
Mem Write
Immediate
Load/Store Instruction Path e.g., sw t0,
100(s0)
8
Write
Registers
Mem Read
Select
Data Memory
0 1
M U X
1 0
M U X
Sign Ext
Mem Write
Immediate
Load/Store Instruction Path e.g., lw t0,
100(s0)
9
25-21
Write
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
Instruction Path with Instruction from Memory
10
Simple Instruction Path, including Incrementing
the Program Counter
4
Detect Zero
25-21
Write
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
11
1 0
M U X
M U X
0 1
Shft Left 2
4
Branch
Detect Zero
25-21
Write
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
Branch Instruction Path e.g., beq s0, zero,
addr
12
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
4
Jump
Detect Zero
25-21
Write
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
Jump Instruction Path e.g., j addr
13
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
4
Jump
and Branch
Detect Zero
25-21
Write
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
14
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
15
Control Lines, Top to Bottom

• A RegDst
• B Jump
• C Branch
• D MemWrite
• E MemToReg
• F ALUOp
• G MemRead
• H ALUSrc
• I RegWrite

16
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Sign Ext
R-Type Start to 10 ns
Mem Write
15-0
ALU CTRL
5-0
17
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
ADD
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
ALU
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
R-Type Register Rd 10-15 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
18
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
ADD
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
ALU
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
R-Type ALU 15-25 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
19
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
ADD
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
ALU
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
R-Type Reg Write 25-30 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
20
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Load Word 0-10 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
21
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Load Word Reg Read 10-15 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
22
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Load Word Address Comp 15-25 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
23
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Load Word Memory Access 25-35 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
24
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
Load Word Memory Access 35-40 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
25
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
BEQ 0-10 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
26
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
BEQ Register Rd 10-15 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0
27
Shft Left 2
25-0
1 0
M U X
M U X
0 1
31-28
Shft Left 2
A B C D E F G H I
4
C O N T R O L
31-26
25-21
Write
Zero
20-16
PC
Instruction Memory
Registers
Mem Read
M U X
0 1
Data Memory
0 1
M U X
15-11
1 0
M U X
BEQ ALU test 15-25 ns
Sign Ext
Mem Write
15-0
ALU CTRL
5-0