2. Consider the following assembly language code: I0: ADD R4 = R1 + R0; I1: SUB
ID: 3822447 • Letter: 2
Question
2. Consider the following assembly language code:
I0: ADD R4 = R1 + R0;
I1: SUB R9 = R3 - R4;
I2: ADD R4 = R5 + R6;
I3: LDW R2 = MEM[R3 + 100];
I4: LDW R2 = MEM[R2 + 0];
I5: STW MEM[R4 + 100] = R2;
I6: AND R2 = R2 & R1;
Assuming no data forwarding, draw the time sequence pipeline diagram and calculate the number of clock cycles needed to complete the whole sequence of instruction.
Assuming forwarding, draw the time sequence pipeline diagram and calculate the number of clocl cycles needed to complete the whole sequence of instruction.
3. Rearrange the following code to avoid/reduce the stall clock cycles
add $3,$2,$1
lw $4,4($3)
addi $6,$4,1
sub $8,$3,$1
Explanation / Answer
2.
Let us consider the following assembly language code:
I0: ADD R4 = R1 + R0;
I1: SUB R9 = R3 - R4;
I2: ADD R4 = R5 + R6;
I3: LDW R2 = MEM[R3 + 100];
I4: LDW R2 = MEM[R2 + 0];
I5: STW MEM[R4 + 100] = R2;
I6: AND R2 = R2 & R1;
The time sequence pipeline diagram (no data forwarding)
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
I0
IF
ID
EX
MEM
WB
I1
IF
ID
X
EX
MEM
WB
I2
IF
ID
X
X
EX
MEM
WB
I3
IF
ID
X
X
EX
MEM
WB
I4
IF
ID
X
X
X
EX
MEM
WB
I5
IF
X
X
X
ID
EX
MEM
WB
I6
X
X
X
IF
ID
EX
MEM
WB
The number of clock cycles needed to complete the whole sequence of instruction is 13.
The time sequence pipeline diagram (with forwarding)
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
I0
IF
ID
EX
MEM
WB
I1
IF
ID
EX
MEM
WB
I2
IF
ID
EX
MEM
WB
I3
IF
ID
EX
MEM
WB
I4
IF
ID
X
EX
MEM
WB
I5
IF
X
ID
EX
MEM
WB
I6
X
IF
ID
EX
MEM
WB
The number of clock cycles needed to complete the whole sequence of instruction is 11.
3. The given code is rearranged below to avoid stall clock cycles:
add $3,$2,$1
lw $4,4($3)
sub $8,$3,$1
addi $6,$4,1
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
I0
IF
ID
EX
MEM
WB
I1
IF
ID
X
EX
MEM
WB
I2
IF
ID
X
X
EX
MEM
WB
I3
IF
ID
X
X
EX
MEM
WB
I4
IF
ID
X
X
X
EX
MEM
WB
I5
IF
X
X
X
ID
EX
MEM
WB
I6
X
X
X
IF
ID
EX
MEM
WB
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