GATE | GATE CS 2018 | Question 61
The 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 instruction is ______ .
Note – This was Numerical Type question.
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)+25*(1-1) = (100 + 4) + 40*2+35*1+25*0 = 104 + 115 = 219 cycles
So, option (A) is correct.