Pipelining

Consider a pipelined processor with the following four stages:

  IF: Instruction Fetch
  ID: Instruction Decode and Operand Fetch
  EX: Execute
  WB: Write Back

The IF, ID and WB stages take one clock cycle each to complete the operation. The number of clock cycles for the EX stage depends on the instruction. The ADD and SUB instructions need 1 clock cycle and the MUL instruction needs 3 clock cycles in the EX stage. Operand forwarding is used in the pipelined processor. What is the number of clock cycles taken to complete the following sequence of instructions?

  ADD R2, R1, R0       R2 <- R0 + R1
  MUL R4, R3, R2       R4 <- R3 * R2
  SUB R6, R5, R4       R6 <- R5 - R4