Q: Are all of these enough to get full marks in the exam?
A: NO. This is a practice sheet. Meaning, you can practice all you want using the
questions from this sheet. However, doing well in exams depends upon your ability
to understand a question, formulate an answer, and express it correctly. You see,
these are humane skills which cannot be guaranteed by completing a practice sheet
only. But yeah, Best of luck anyway.
Chapter 4 (The Processor)
Question - 1:
Draw a diagram of the register file, clearly indicating all input and output pins.
a. Provide a detailed explanation of how the register file performs both read and
write operations.
b. Explain why the size of the read/write register pin is 5 bits.
Question - 2:
Draw a diagram of the ALU, clearly indicating all input and output pins.
a. Explain the significance of the Zero pin in the ALU.
b. Describe how the ALU determines which operation to perform on the given
inputs.
Question - 3:
Draw a diagram of the ALU Control, clearly indicating all input and output pins.
a. Does the ALU control utilize Instruction bits 30 and 14-12 to generate the output
for the LD instruction? Provide a justification for your answer.
b. Identify the specific cases in which the ALU control utilizes Instruction bits 30
and 14-12 to generate the output. Additionally, explain why only these four bits
(Instruction bits 30 and 14-12) are used in such cases.
Question - 4:
Identify the necessary resources or components from the list provided to construct
the datapath for each of the following instructions.
PC Instruction Data Register A Immediate Control ALU
Memory Memory File L Generation Unit Control
U Unit
i. ADD X21, X22, X23
ii. AND X21, X22, X23
iii. OR X21, X22, X23
iv ADDi X21, X22, 5
v. LD X21, 22(X21)
vi. SD X21, 22(X21)
vii BEQ X21, X22, End
Question - 5:
Draw a simplified datapath with control unit that can process ADD X21, X22, X23
Question - 6:
Draw a simplified datapath with control unit that can process ADDI X21, X22, 5
Question - 7:
Draw a simplified datapath with control unit that can process LD X21, 14(X22)
Question - 8:
Draw a simplified datapath with control unit that can process only the following
codes:
LD X21, 14(X22)
SD X22, 16(X21)
Mention the control signals also for each instructions.
Question - 9:
Draw a simplified datapath with control unit that can process only the following
codes:
ADDI X21, X22, 5
LD X21, 14(X22)
Mention the control signals also for each instructions.
Question - 10:
Draw a simplified datapath with control unit that can process the following codes:
ADDI X21, X22, 5
LD X21, 14(X22)
Mention the control signals also for each instructions.
Question - 11:
Modify the BEQ datapath so that it works for BNE.
Question - 12:
Construct a single-cycle full-datapath, ensuring that you use only 4:1
multiplexer(s) wherever multiplexer(s) are required.
Question - 13:
Suppose that in a buggy implementation of the RISC V datapath, the AND gate for
the branching decision was replaced with an XNOR gate. Describe how this error
would affect the execution of the following instruction.
i. SUB x1, x2, x3 [3 points]
ii. BEQ x1, x2, target [3 points]
Question - 14:
Determine the values of the following control bits when executing the instruction
"Add X21, X22, X23" in the provided single-cycle datapath.
Branch MemWrite RegWrite ALUSrc
Question - 15:
Determine the values of the following control bits when executing the instruction
"Addi X21, X22, X23" in provided single-cycle datapath for Q-14
Branch MemWrite RegWrite ALUSrc
Question - 16:
Determine the values of the following control bits when executing the instruction
"Add X21, X22, X23" in the provided single-cycle datapath.
Branch ALUSrc RegWrite MemToReg
Question - 17:
Study the above RISC-V Datapath thoroughly. Assume that initially PC=600h, x1 =
222h, x2 = 444h, x3 = 666h, x4=999h.
Determine the values of A, B, C, D, E in hex for the instructions executed
sequentially. If the value does not matter, write it as X (don’t care)
A B C D E
i. sub x1, x2, x1
ii. sd x4, 12(x2)
Question - 18:
Carefully examine the RISC-V datapath provided in Q-17. Assume the initial
values are: PC = 600h, x1 = 222h, x2 = 444h, x3 = 666h, and x4 = 999h. For the
following instructions executed sequentially, determine the hexadecimal values
of A, B, C, D, and E. If the value is irrelevant, indicate it as X (don't care).
i. sub x1, x2, x1
ii. sd x4, 12(x2)
PC A B C D E
iii. Addi x1, x1, 12
Question - 19:
Given the following code sequence:
1. ADD X1, X2, X3
2. LD X5, 10(X4)
3. OR X2, X3, X23
Is it possible to execute this code sequence using the provided datapath? If not,
correct the datapath.
Question - 20:
PC = 0x0040ABCD123045B1
Instruction Memory: Data Memory:
Address Content Address Content
0x40ABCD123045AD 0111 0101 0x40ABCD123045AD 0111 0101
………………………… 1011 1110 ………………………… 0111 0100
………………………… 1001 0001 ………………………… 1000 0000
………………………… 1100 0000 ………………………… 1000 0001
………………………… 0000 0001 ………………………… 0000 0000
………………………… 1001 0101 ………………………… 0001 0111
………………………… 0000 0101 ………………………… 1000 0101
………………………… 0011 0011 ………………………… 1111 0011
Fetch the instruction from memory. Convert your answer in Hex.
Question - 21:
The following table shows the different stages involved in executing instructions
and the corresponding durations for each stage:
stages Instruction Register ALU Memory Register
Fetch Read Op Access Write
Duration 50ps 10ps 30ps 20ps 10ps
Given the above durations, determine the total time required to complete each of
the following instructions:
Instructions Time to complete each
instructions
i. ADD X21, X22, X23
ii. AND X21, X22, X23
iii. OR X21, X22, X23
iv ADDi X21, X22, X23
v. LD X21, 22(X21)
Instructions Time to complete each
instructions
vi. SD X21, 22(X21)
vii BEQ X21, X22, End
Question - 22:
Instruction Time (PS)
Add X21, X22, X23 10
Sub X21, X23, X24 20
Mul X22, X23, X26 15
LD X22, 0(X21) 25
The above instructions are being run in a single cycle datapath.
a. Now determine what is the clock period of this system?
b. What would be the total time to run this instruction sequence?
Question - 23 :
What do you understand by the term "single-cycle" in the context of a single-cycle
datapath?
Question - 24 :
Stage IF ID EX MEM WB
Time (PS) 10 20 20 20 10
The below instructions are being run in a pipelined datapath. Calculate the time
required to execute each instruction.
Instruction Time (PS)
Add X21, X22, X23
Sub X21, X23, X24
Mul X22, X23, X26
LD X22, 0(X21)
Determine what is the clock period of this system?
Question - 25 :
Write a comparison between the single cycle datapath and a pipelined datapath.
Mention why pipelined datapath is implemented in real life.
Question - 26 :
In the RISC-V pipelined datapath we have 5 stages. Can we divide these 5 stages
into more stages to make the datapath more efficient?
Question - 27 :
Explain Why do data hazards occur in a pipelined Data path?
Question - 28 :
The instructions provided below are executed sequentially within a pipelined
datapath that is divided into five stages, as depicted in the following diagram. In
the diagram, the gray shaded areas represent the periods when tasks are actively
being processed in each stage, whereas the unshaded (white) areas indicate inactive
portions of each stage.
Instruction
Add X21, X22, X23
Sub X21, X21, X24
Mul X22, X21, X26
LD X22, 0(X21)
Will any data hazards occur during the execution of this instruction set? If so,
identify the number of data hazards and clearly circle them.
Question - 29 :
What do you understand about structural hazards? Explain with an example.
Question - 30 :
The instructions provided below are executed sequentially within a pipelined
datapath that is divided into five stages, as depicted in the following diagram. In
the diagram, the gray shaded areas represent the periods when tasks are actively
being processed in each stage, whereas the unshaded (white) areas indicate inactive
portions of each stage.
Instruction
Add X21, X22, X23
Sub X21, X20, X24
LD X22, 0(X22)
a. Will any data hazards occur during the execution of this instruction set? If so,
identify the number of data hazards and clearly circle them.
b. How many clock cycles are necessary to run this instruction set?
Question - 31 :
The following are the time requirements for various stages of a datapath:
1. Instruction Fetch: 25 ps
2. Instruction Decode: 10 ps
3. Register Read: 15 ps
4. Arithmetic or Logical task execution: 20 ps
5. Data Memory Read: 20 ps
6. Data Memory Write: 20 ps
7. Register Write: 25 ps
You are given the following instruction set, executed sequentially:
1. Add X21, X22, X23
2. Sub X21, X23, X24
3. Mul X22, X22, X26
4. LD X22, 0(X20)
Suppose this instruction set is executed sequentially in a single cycle datapath.
Answer the following:
a. Calculate the actual time required to execute each instruction.
b. Determine the clock period of this system.
c. Calculate the number of clock cycles needed to execute this instruction set.
d. Determine the total time required to execute this instruction set.
Now, assume the instruction set is executed sequentially in an ideal pipelined
datapath with 5 stages.
Answer the following:
a. Calculate the actual time required to execute each instruction.
b. Determine the clock period of this system.
c. Calculate the number of clock cycles needed to execute this instruction set.
d. Determine the total time required to execute this instruction set.
