落了一節課，直接lecture3

Lecture3 Basic Pipeline

1、Single-cycle implementation: seldom used

     取指  譯碼  執行  讀mem/cache  寫回WB

2、How to make it fast?

     To decrease the clock cycle time? difficult!

     What's the problem？資源浪費 序列 Start work ASAP

3、Multi-cycled implemention

4、Pipelining

    why pipelining？ decrease CPUtime  improving the throughput 

5、Pipeline hazard: the major hurdle

    A hazard is a condition that prevents an instruction in the pipe from excuting its next scheduled pipe stage

   Taxonomy of hazard:

   Structrural hazards: These are comflicts over hardzards resources.

   Data hazards: Instruction depends on result of prior computation which is not ready yet.

   Control hazards: PC are not available in time to fetch an instruction on the next clock.

6、 Hazards can always be resolved by stall

 7、浮點數運算：解決結構競爭（Structrural hazards）

      方法1：fully pipelined adder：overhead（體積、執行時間）過大

      方法2：multiple unpipelined adder：overhead（成本）過大

      方法3：插入stall

8、coping with data hazards

    方法1：增加資料通路（Forwarding Path）

    方法2：Forwarding not always work，so implement load Interlock ：load指令比較常見，這個方法開銷較大

    方法3：編譯器端,進行程式碼排程，進行程式碼塊順序改變