Question

The lui instruction in the following instruction sequence is fetched in cycle 1 on our pipeline that includes both a data hazard unit and a forwarding unit. Indicate the total number of clock cycles consumed by this code running on the pipeline with no branch prediction and no instruction rearrangement. The bltz instruction IS a delayed branch. The bltz instruction branches to the instruction with label "loop" if register $12 contains a value that is less than 0

Answer 1

The question pertains to the total number of clock cycles needed for a sequence of instructions to execute on a pipelined processor with a delayed branch.

Step-by-step explanation:

The student is asking about the number of clock cycles consumed by a sequence of instructions on a pipelined processor with specific hardware units, such as a data hazard unit and a forwarding unit, as well as a delayed branch without any branch prediction or instruction rearrangement. Given that the branch is a delayed branch, the branch will not be taken immediately; instead, the next instruction following the branch will be executed regardless of whether the branch condition is true or not.

This implies that we have a classic 5-stage Instruction Pipeline which includes stages such as Fetch, Decode, Execute, Memory access, and Write back. Without knowing the exact number of instructions or the full sequence, a precise cycle count cannot be given. However, generally speaking, each instruction would pass through five stages, with the potential for data hazards that may cause stalls (assuming the data hazard unit cannot completely eliminate them), especially if there are dependencies between consecutive instructions.

These stalls would increase the number of cycles. Furthermore, the branch delay means that at least one additional instruction is executed after the branch, irrespective of whether the branch condition is met or not. This too must be factored into the total cycle count.