Chapter 4, Problem 4.19.3E

Explanation of Solution

Changes that are to be made in the pipeline design:

• For all the instructions the instruction memory is being read.
• For every instructions two register read is being performed even though there is a single value that is being used actually but the register value which is not used can be avoided from being read.
• The process is done by adding the control inputs of RegRead1 and RegRead2 to the register unit.
• The register unit will enable or disable the read that is performed on the register.
• The control signals need to be generated quickly such that it avoids the clock cycle time being lengthened.

Energy spent before the change:

The energy spent for the load instruction is computed as shown below:

$\begin{array}{c}\text{Energy}\text{=}\text{I-Mem}\text{+2×}\text{RegisterRead}\text{+}\end{array}$