CS 3853 Computer Architecture Chapter 3 Section 4 Example Answers

Question: The last instruction modified F6 before the previous instruction which uses F6 starts to execute. Is this a problem.

Instruction		Reservation Station	Execution Unit	Issue Cycle	Ex Start Cycle	Ex End Cycle	Memory Cycle	CDB cycle	Write dest
L.D	F6,32(R2)	Load1	ALU	1	2	2	3	4	F6
L.D	F2,44(R3)	Load2	ALU	2	3	3	4	5	F2
MUL.D	F0,F2,F4	Mult1	fmul	3	6	15		16	F0
SUB.D	F8,F2,F6	Add1	fadd	4	6	7		8	F8
DIV.D	F10,F0,F6	Mult2	fmul	5	17	56		57	F10
ADD.D	F6,F8,F2	Add2	fadd	6	9	10		11	F6

Note: It is not a problem since the Mult2 reservation unit stores the operand from F6 at the time it issues (cycle 5) which is before it is modified by the last instruction.