103年 - 103 國立中山大學_碩士班招生考試_電機系(己組)：計算機結構#110065

[Problem 2] Suppose we are considering a change to an instruction set. The base machine is a load-store machine. Measurements of the load-store machine showing the instruction mix and clock cycle counts per instructions are given in the following table:

       Let's assume that 25% of the ALU operations directly use a loaded operand that is not used again. We propose adding ALU instructions that have one source operand in memory. These new register-memory instructions have a clock cycle count of 2. Suppose that the extended instruction set increases the clock cycle count for branches by 1, but it does not affect the clock eycle time, Would this change improve CPU performance? Explain your answer. (20%)

[Problem 5] Use the following code fragment:

Loop:
     Assume the initial value of R3 is R2+200. Use the five-stage instruction pipeline ( IF, DEC, EXE, MEM, WB) and assume all memory accesses are one cycle operation. Furthermore, branches are resolved in MEM.
    Show the timing of this instruction sequence for the five-stage instruction pipeline with normal forwarding and bypassing hardware. 

    Assume that branch is handled by predicting it has not taken. How many cycles does this loop take to execute? (10%) Assuming the five-stage instruction pipeline with a single-cycle delayed branch and normal forwarding and bypassing hardware, schedule the instructions in the loop including the branch- delay slot. You may reorder instructions and modify the individual instruction operands, but do not undertake other loop transformations that change the number of op-code of instructions in the loop. Show a pipeline timing diagram and compute the number of eyeles needed to execute the entire loop. (15%