Single-Cycle-dp

Single-Cycle-dp - 6/16/2008 1 The Processor: Datapath and...

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Unformatted text preview: 6/16/2008 1 The Processor: Datapath and Control 6/16/2008 2 A single-cycle MIPS processor An instruction set architecture is an interface that defines the hardware operations which are available to software. Any instruction set can be implemented in many different ways. Over the next few weeks well see several possibilities. In a basic single-cycle implementation all operations take the same amount of timea single cycle. A multicycle implementation allows faster operations to take less time than slower ones, so overall performance can be increased. Finally, pipelining lets a processor overlap the execution of several instructions, potentially leading to big performance gains. 6/16/2008 3 Single-cycle implementation In lecture, we will describe the implementation a simple MIPS-based instruction set supporting just the following operations. Today well build a single-cycle implementation of this instruction set. All instructions will execute in the same amount of time; this will determine the clock cycle time for our performance equations. Well explain the datapath first, and then make the control unit. Arithmetic: add sub and or slt Data Transfer: lw sw Control: beq 6/16/2008 4 Computers are state machines A computer is just a big fancy state machine . Registers, memory, hard disks and other storage form the state. The processor keeps reading and updating the state, according to the instructions in some program. State Control 6/16/2008 5 John von Neumann In the old days, programming involved actually changing a machines physical configuration by flipping switches or connecting wires. A computer could run just one program at a time. Memory only stored data that was being operated on. Then around 1944, John von Neumann and others got the idea to encode instructions in a format that could be stored in memory just like data. The processor interprets and executes instructions from memory. One machine could perform many different tasks, just by loading different programs into memory. The stored program design is often called a Von Neumann machine . 6/16/2008 6 Memories Its easier to use a Harvard architecture at first, with programs and data stored in separate memories. The dark lines here represent 32-bit values, so these are 2 32 B x 8 b/B memories. Blue lines represent control signals. MemRead and MemWrite should be set to 1 if the data memory is to be read or written respectively, and 0 otherwise. When a control signal does something when it is set to 1, we call it active high (vs. active low) because 1 is usually a higher voltage than 0. For today, we will assume you cannot write to the instruction memory ....
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This note was uploaded on 09/01/2009 for the course COE 0142 taught by Professor Staff during the Summer '08 term at Pittsburgh.

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Single-Cycle-dp - 6/16/2008 1 The Processor: Datapath and...

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