Pipeline

Question

An instruction pipeline has stages as given in diagram

A program consistsing of 9 instruction I1,I2....I9 is executed in this pipeline processor.instruction I3 is the only conditional branch instruction and its branch target is I7,If the branch taken after EI state,the time needed to complete the program is?

Answer 1

The maximum delay is taken by the stage FO which is 11ns.

The Buffer Delay is 1ns.

Hence, each stage takes maximum 11+1 = 12ns

I1	FI	DI	FO	EI	WO
I2		FI	DI	FO	EI	WO
I3			FI	DI	FO	EI	WO
I7							FI	DI	FO	EI	WO
I8								FI	DI	FO	EI	WO
I9									FI	DI	FO	EI	WO

Hence, Total stages = 13

Therefore, total time = 13*12 = 156ns

Comments

but, It is not said that , pipleline is synchronous.  ??

time to complete I1 = 39 ns or 60 ??  

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I think I1=60ns only because I tried this type of question from GATE and also on Made Easy site and everywhere they have done it like this, even though they haven't explicitly mentioned that the pipeline is synchronous.

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@Vijay. This is just a point in the execution of large no. of instructions.

So, it will definitely be 60.

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Similar To
https://gateoverflow.in/330/gate2013_45