hpca/SampleMidterms/Midterm1/problem5

Problem 5. [15 points] ROB

A processor with a ROB is executing the following sequence of instructions and, for each instruction, we show the cycle in which the instruction is fetched, decoded, issued, begins to execute, and writes result. This is really the same processor and the same instruction sequence as in Problem 3, except that a ROB has been added.

table2.jpg

  1. [3 points] For instructions I1-I5 in the table above, write-in the cycle in which each instruction commits. Be careful, these five points are given on an all-or-nothing basis (you get all 5 points if and only if all 5 commit times are correct).

  2. [4 points] If this processor had 8 reservation stations for the adder and 8 for the multiplier, instructions I1 through I5 would still issue as shown above, but I6 would issue in cycle 9. What is size of the ROB? ______ entries. Explain:

  3. [8 points] Suppose that, instead of completing normally, I4 detects an overflow exception when it executes (in cycle 11). What happens in the next 5 cycles:

             Cycle 12:
    
             Cycle 13:
    
             Cycle 14:
    
             Cycle 15:
    
             Cycle 16: