Processor design: Difference between revisions

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The mode of operation of any processor is the execution of lists of instructions. Instructions typically include those to compute or manipulate data values using [[Processor register|registers]], change or retrieve values in read/write memory, perform relational tests between data values and to control program flow.

Processor designs are often tested and validated on one or several FPGAs before sending the design of the processor to a foundry for [[semiconductor fabrication]].<ref>{{cite web|url=https://www.anandtech.com/show/14798/xilinx-announces-world-largest-fpga-virtex-ultrascale-vu19p-with-9m-cells|archive-url=https://web.archive.org/web/20190827160514/https://www.anandtech.com/show/14798/xilinx-announces-world-largest-fpga-virtex-ultrascale-vu19p-with-9m-cells|url-status=dead|archive-date=August 27, 2019|title=Xilinx Announces World Largest FPGA: Virtex Ultrascale+ VU19P with 9m Cells|first=Ian|last=Cutress|date=August 27, 2019|website=[[AnandTech]]}}</ref>

== Details ==

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=== Basics ===

CPU design is divided into multiple components. Information is transferred through [[datapath]]s (such as [[Arithmetic logic unit|ALUs]] and [[Pipeline (computing)|pipelines]]). These datapaths are controlled through logic by [[control unit]]s. [[Memory (computing)|Memory]] components include [[register file]]s and [[Cache (computing)|caches]] to retain information, or certain actions. [[Clock signal|Clock circuitry]] maintains internal rhythms and timing through clock drivers, [[Phase-locked loop|PLLs]], and [[clock distribution network]]s. Pad transceiver circuitry withwhich allows signals to be received and sent and a [[logic gate]] cell [[Library (electronics)|library]] which is used to implement the logic. Logic gates are the foundation for processor design as they are used to implement most of the processor's components.<ref>{{cite book | url=https://books.google.com/books?id=GBVADQAAQBAJ&q=processor+logic+gates | title=Digital Systems: From Logic Gates to Processors | isbn=978-3-319-41198-9 | last1=Deschamps | first1=Jean-Pierre | last2=Valderrama | first2=Elena | last3=Terés | first3=Lluís | date=12 October 2016 | publisher=Springer }}</ref>

CPUs designed for high-performance markets might require custom (optimized or application specific (see below)) designs for each of these items to achieve frequency, [[power consumption|power-dissipation]], and chip-area goals whereas CPUs designed for lower performance markets might lessen the implementation burden by acquiring some of these items by purchasing them as [[intellectual property]]. Control logic implementation techniques ([[logic synthesis]] using CAD tools) can be used to implement datapaths, register files, and clocks. Common logic styles used in CPU design include unstructured random logic, [[finite-state machine]]s, [[microprogramming]] (common from 1965 to 1985), and [[Programmable logic array]]s (common in the 1980s, no longer common).