GATE CS 2010 Q33 — Instruction Pipelining

A $5-$stage pipelined processor has Instruction Fetch (IF), Instruction Decode (ID), Operand Fetch (OF), Perform Operation (PO) and Write Operand (WO) stages. The IF, ID, OF and WO stages take $1$ clock cycle each for any instruction. The PO stage takes $1$ clock cycle for ADD and SUB instructions, $3$ clock cycles for MUL instruction and $6$ clock cycles for DIV instruction respectively. Operand forwarding is used in the pipeline. What is the number of clock cycles needed to execute the following sequence of instructions?

$$\begin{array}{|c|l||} \hline \textbf{Instruction} & \textbf{Meaning of instruction} \\ \hline \text{$t \_0$: MUL $R \_2$,$R \_0$,$R \_1$} & \text{R}_2 \gets \text{R}_0*\text{R}_1\\ \hline \text{$t \_1$: DIV $R \_5,R \_3,R \_4$} & \text{R}_5 \gets \text{R}_3 ∕ \text{R}_4\\ \hline \text{$t \_2$: ADD $R \_2,R \_5,R \_2$} & \text{R}_2 \gets \text{R}_5 + \text{R}_2 \\ \hline t_3: \text{SUB} \:\text{R}_5,\text{R}_2,\text{R}_6 & \text{R}_5 \gets \text{R}_2 - \text{R}_6 \\ \hline\end{array}$$