Gate2018 cs Q40

40The instruction pipeline of a RISC processor has the following stages. Instruction Fetch (IF), Instruction Decode (ID), Operand Fetch (OF), Perform Operation (PO) and Writeback (WB). The IF, ID, OF and WB stages take 1 clock cycle each for every instruction. Consider a sequence of 100 instructions. In the PO stage, 40 instructions take 3 clock cycles each, 35 instructions take 2 clock cycles each, and the remaining 25 instructions take 1 clock cycle each. assume that there are no data hazards and no control hazards. The number of clock cycles required for completion of execution of the sequence of instructions is ____________.

Note – Numerical Type question

Option : A
Explanation :
Given, total number of instructions (n) = 100
Number of stages (k) = 5
Since, if n instructions take c cycle, so (c-1) stalls will occur for these instructions.
Therefore, the number of clock cycles required = Total number of cycles required in general case + Extra cycles required (here, in PO stage)
= (n + k – 1) + Extra cycles
= (100 + 5 -1) + 40*(3-1)+35*(2-1)+20*(1-1)
= (100 + 4) + 40*2+35*1+20*0
= 104 + 115
= 219 cycles

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