CSE/EEE 230 – Assignment 4
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Show all the steps in your solution to receive full credit.
Question 1: The following MIPS Code is executed using the single cycle MIPS architecture. Include
all iterations of the loop while answering the questions.
Start: addiu $t6, $0, 64
addi $t8, $0, 8
add $s1, $s0, $t8
Loop: slt $t0, $s0, $s1
beq $t0, $0, Exit
lbu $t1, 0($s0)
sub $t1, $t1, $t6
sb $t1, 0($s0)
addi $s0, $s0, 1
j Loop
Exit:
(a) Data Path – For the given code, write the Functional Units used in order.
• Specify if any Functional Units (FUs) are used at the same time for the same instruction,
for example PC+4 Adder is used while Instruction Memory is in use.
• For Multiplexors, if the output of the MUX is used, then it implies that the MUX is used
(i.e., if the select lines are 0 or 1 and not don’t cares, then the MUX is used). Similarly, if
any FU output is unused, we assume that the FU is unused.
• You may group the instructions with the same datapath.
• You may use the following notations for the Functional Units or the image on the next
page.
Instruction Memory (IM), Data Memory (DM), Register File (RF), Arithmetic and Logical Unit
(ALU), Program Counter Register (PC), Sign Extension block (SE), Control Unit (ctrl1), ALU control
unit (ctrl2), PC+4 Adder (add1), Branch PC target Adder (add2), Shift Left 2 (sll), Regdst MUX
(mux1), ALUSrc MUX (mux2), MemtoReg MUX (mux3), PCSrc MUX (mux4), Jump MUX (mux5).
(b) Control Path – For the given code, write the values of the control signals for each instruction.
• You may group the instructions with the same control signals.
• The control signals to be included are: ALUOp, ALU control output (ALU ctrl),
Branch, Jump, PCSrc, Regdst, ALUSrc, MemtoReg, RegWrite, MemRead and
MemWrite
Instr ALU
Op
ALU
ctrl
Reg
dst
ALU
Src
Memto
Reg
Branch Jump PC
Src
Reg
Write
Mem
Read
Mem
Write
(c) Execution Time – For the given code, compute the execution time for each instruction and for
the complete code based on the following information.
(i) Given the following access times for the critical functional units, compute the time taken
to execute each instruction.You may group the instructions with the same execution time.
Memory Access = 0.25ns;
Register Access = 0.13ns;
ALU execution = 0.18ns
(ii) Assuming all instructions are executed using a fixed clock cycle length. What is the
execution time for the complete code/program?
Question 2: The following MIPS Code is executed using the MIPS multicycle architecture. Include
all iterations of the loop. Initial values for the registers are: $s0 = 0x230, $s1 = 0x240 and $t1 = 1
Loop: slt $t0, $s0, $s1
beq $t0, $0, Exit
lbu $t1, 0($s0)
sub $t1, $t1, $t6
sb $t1, 0($s0)
add $s0, $s0, $t1
j Loop
Exit:
(a) Data Path – For the given code, trace the steps of execution using the image below.
(b) Control Path – For the given code, write the values of the control signals for each instruction.
• You may group the instructions with the same control signals.
• The control signals to be included are: ALUOp, ALU control output (ALU ctrl), IorD,
ALUSrcA, ALUSrcB, IRWrite, PCWrite, PCWriteCond, PCSource, Regdst, RegWrite,
MemRead and MemWrite
(c) Execution Time – For the given code, compute the execution time for the program with
Processor clock rate 4GHz.
Question 3: The following MIPS Code is executed using the MIPS pipeline architecture. Include
all iterations of the loop. For the given code, write the Pipeline Implementation by resolving all
the three hazards using stalls or Hardware, based on the provided assumptions for each part.
Start: addiu $s1, $0, 0x1234
addi $s0, $0, 0x122C
Loop: lb $t1, 0($s0)
sb $t1, 2($s0)
nor $t2, $t1, $t1
sb $t2, 0($s0)
addi $s0, $s0, 4
bne $s0, $s1, Loop
Exit: addi $s0, $0, 0x122C
(a) Consider the following assumptions: (only structural hazards are resolved in hardware, other
hazards have to be resolved with stall/nop.)
• There is separate instruction and data memory access.
• Register read and write can happen within the same clock cycle.
• There is NO Forwarding unit and NO Hazard detection Unit.
• Use stall if an instruction is delayed after fetch.
• Use nop if an instruction is delayed before fetch.
(b) Consider the following assumptions: (structural and data hazards are resolved using
hardware, other hazards have to be resolved with stall/nop.)
• There is separate instruction and data memory access.
• Register read and write can happen within the same clock cycle.
• There is Forwarding unit. Show data forwarding between the correct stages, wherever
necessary.
• There is NO Hazard detection Unit, i.e., no resolution for control hazards in hardware.
• Use stall if an instruction is delayed after fetch.
• Use nop if an instruction is delayed before fetch.
(c) Consider the following assumptions: (all hazards are resolved using hardware)
• There is separate instruction and data memory access.
• Register read and write can happen within the same clock cycle.
• There is Forwarding unit. Show data forwarding between the correct stages, wherever
necessary.
• There is Hazard detection Unit to detect mispredictions and flush if necessary.
• The 2-bit branch prediction scheme is used with initial prediction being weakly Not Taken.
• There is Branch target Buffer (BTB) containing target address for the branch instruction.
• Use stall if an instruction is delayed after fetch.
• Use nop if an instruction is delayed before fetch.
Question 4: The following MIPS Code is executed using the MIPS 2-issue pipeline architecture.
Include all iterations of the loop. For the given code, show the steps in unrolling the loop and
write the 2-issue VLIW pipeline representing the order of issuing the instructions from the loop
unrolled code.
Start: addi $s0, $s1, 32
Loop: lb $t1, 0($s0)
sb $t1, 2($s0)
nor $t2, $t1, $t1
sb $t2, 0($s0)
addi $s0, $s0, -8
bne $s0, $s1, Loop
Exit:
