Data Hazards

• So far we ignored instructions dependencies, but in a real machine one must deal with dependencies.

• Example:

sub $2, $1, $3

and $12, $2, $5 # $12 depends on the result in $2

or $13, $6, $2 # but $2 is updated 3 clock

add $14, $2, $2 # cycles later.

sw $15, 100($2) # We have a problem!!

Clock

Cycle 1

Cycle 2

Cycle 3

Cycle 4

Cycle 5

Cycle 6

Cycle 7

Cycle 8

0: sub

4: and

8: or

12: add

16: sw

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