Question

Identify ALL of the data dependencies in the following code. Which dependencies are data hazards that can be resolved by forwarding? For each irresolvable data hazard, how many pipeline stalls will occur and in which instruction? Draw pipeline stages in the form of "IF ID EX MEM WB" to show stalls.
a. add $12, $15, $14b. lw $15, 100($12)c. sub $13, $15, $12d. add $12, $15, $13

Answer 1

Answer:

See the explanation for the answer.

Explanation:

add $12, $15, $14   IF   ID   EX   MEM   WB

lw $15, 100($12)       IF   ID    EX   MEM1   MEM2   WB

sub $13, $15, $12           IF   ID   EX   MEM1   WB

add $12, $15, $13                IF   ID   EX   MEM   WB

sub $13,$15,$12 - dependencies-$15,$12

          hazards-$12-read before write data hazard - can be solved through forwarding

              $15-structural hazard-stalled by 3 clock cycle (if no forwarding)

                      -stalled by 1 clock cycle (if forwarding is present)

add $12,$15,$13 - dependencies $15,13

          hazards-$12,$15-read before write data hazard - can be solved through forwarding