Given these timings for individual stages of the datapath: IF: 120ps ID: 50ps EX

Question

Given these timings for individual stages of the datapath:

IF: 120ps

ID: 50ps

EX: 150ps

MEM: 140ps

WB: 100ps

(a) What is the clock cycle time of a single cycle processor? Explain.

(b) How long does it take for a sub instruction to execute on the single cycle processor?

(c) What is the clock cycle time of a multi-cycle processor? Explain.

(d) How long does it take for a slt instruction to execute on the multi-cycle processor?

(e) What would the cycle time of a single cycle processor be, if the EX stage now takes 130ps?

(f) What would the cycle time of a multi-cycle processor be, if the EX stage now takes 130ps?

Explanation / Answer

IF: 120ps
ID: 50ps
EX: 150ps
MEM: 140ps
WB: 100ps

1)
Clock cycle time = 120 + 50 + 150 + 140 + 100 = 560 ps (single cycle processor)

2)
sub instruction to execute on the single cycle processor ; it takes time = 1 cycle = 560 ps

3)
Clock cycle time = 150 ps (multi-cycle processor ) (i.e clock cycle time = time of the longest stage)

4)
slt instruction to execute on the multi-cycle processor takes time = 1 cycle = 150 ps

5)
if the EX stage now takes 130 ps;
then the cycle time will be = 540 ps

6)
if the EX stage now takes 130 ps
then the cycle time wil be = 140 ps (clock cycle time = longest time taken by an individual stage ; in this case = MEM stage)

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