L4 - 1 ECS 154B Computer Architecture II Winter 2008...

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Unformatted text preview: 1 ECS 154B Computer Architecture II Winter 2008 Multi-Cycle MIPS §5.5 Adapted from slides by Mary Jane Irwin, Penn State 2 Reasons for Multi-cycle Operation • Single cycle CPU wasteful – Clock period must accommodate slowest instruction – Multiple functional units (memory, adders) • Multiple cycle CPU better – Clock period is determined by longest operation – Functional units can be shared • Reduces chip area • However, only one use per clock cycle – Instructions can take a different number of clock cycles to complete – Prepares you for introduction of pipelining 3 Multi-cycle Approach • Let instructions take more than one clock cycle – Break instruction into steps that occur in one cycle • Balance steps to minimize clock period • Each resource used only once per step – Not all instructions need every step • Reuse resources to save chip area – ALU used to calculate PC+4 and branch offset in addition to instruction operation – Single memory for instructions and data 4 Multi-cycle Approach • Single cycle CPU • Multi-cycle CPU – Requires state elements to hold intermediate values State element State element Combinational logic clock one clock cycle or instruction State Element A Combinational logic State Element B … State Element N-1 Combinational logic State Element N clock one instruction … one clock cycle 2 5 Multi-cycle Approach • Each cycle must – Store values needed in a later cycle of the current instruction in an internal register. All except IR hold data for one clock cycle....
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This note was uploaded on 05/06/2008 for the course ECS 154b taught by Professor Krado during the Winter '08 term at UC Davis.

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L4 - 1 ECS 154B Computer Architecture II Winter 2008...

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