Place and route is a stage in the design of

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

integrated circuits An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

, and

field-programmable gate array A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware d ...

s. As implied by the name, it is composed of two steps, placement and

routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...

. The first step, placement, involves deciding where to place all

electronic components An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not ...

circuitry An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electrical ...

, and

logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premises ...

elements in a generally limited amount of space. This is followed by routing, which decides the exact design of all the wires needed to connect the placed components. This step must implement all the desired connections while following the rules and limitations of the manufacturing process. Place and route is used in several contexts: *

Printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

s, during which

component Circuit Component may refer to: •Are devices that perform functions when they are connected in a circuit. In engineering, science, and technology Generic systems *System components, an entity with discrete structure, such as an assemb ...

s are graphically placed on the board and the wires drawn between them *

Integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s, during which a

layout Layout may refer to: * Page layout, the arrangement of visual elements on a page ** Comprehensive layout (comp), a proposed page layout presented by a designer to their client * Layout (computing), the process of calculating the position of obje ...

of a larger block of the circuit or the whole circuit is created from layouts of smaller sub-blocks *

FPGA A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware de ...

s, during which

elements are placed and interconnected on the grid of the FPGA These processes are similar at a high level, but the actual details are very different. With the large sizes of modern designs, this operation is usually performed by

electronic design automation Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...

(EDA) tools. In all these contexts, the final result when placing and routing is finished is the "layout", a geometric description of the location and rotation of each part, and the exact path of each wire connecting them. Occasionally some people call the entire place-and-route process "layout".

Printed circuit board

The design of a printed circuit board comes after the creation of a

schematic A schematic, or schematic diagram, is a designed representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the sc ...

and generation of a

netlist In electronic design, a netlist is a description of the connectivity of an electronic circuit. In its simplest form, a netlist consists of a list of the electronic components in a circuit and a list of the nodes they are connected to. A network ...

. The generated netlist is then read into a layout tool and associated with the footprints of the devices from a library. Placing and routing the devices can now start. Placing and routing is generally done in two steps. Placing the components comes first, then

the connections between the components. The placement of components is not absolute during the routing phase, as it may still be changed by moving and rotating, especially with designs using more complex components such as FPGAs or microprocessors. Their large number of

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

s, and their

signal integrity Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. However, digital signals are fundamentally analog in nature, ...

needs may require optimization of the placement. The resulting design is then output in RS-274X

Gerber format The Gerber format is an open format, open ASCII file formats#Vector formats, vector format for printed circuit board (PCB) designs. It is the de facto standard used by PCB industry software to describe the printed circuit board images: copper la ...

to load in the CAM system of the manufacturer. In contrast to an IC layout, where the entire finished layout is stored in one graphics file, different files and formats are needed for PCB manufacture. The fabrication data consists of a set of Gerber files, a drill file, and a pick-and-place file containing the location and alignment of the devices generated for automated placement of the devices in the assembly process.

Field-programmable gate array

The process of placing and routing for an FPGA is generally not performed by a person, but uses a tool provided by the FPGA Vendor or another software manufacturer. The need for software tools is because of the complexity of the circuitry within the FPGA and the function the designer wishes to perform. FPGA designs are described using logic diagrams containing

digital logic A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more Binary number, binary inputs that produces a single binary output. Depending on the context, the term may refer to an id ...

and

hardware description languages In computer engineering, a hardware description language (HDL) is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits. A hardware description language en ...

such as

VHDL The VHSIC Hardware Description Language (VHDL) is a hardware description language (HDL) that can model the behavior and structure of digital systems at multiple levels of abstraction, ranging from the system level down to that of logic gates ...

and

Verilog Verilog, standardized as IEEE 1364, is a hardware description language (HDL) used to model electronic systems. It is most commonly used in the design and verification of digital circuits at the register-transfer level of abstraction. It is also ...

. These will then be put through an automated place-and-route procedure to generate a pinout, which will be used to interface with the parts outside of the FPGA.

Integrated circuits

The IC place-and-route stage typically starts with one or more schematics, HDL files, or pre-routed

IP core In electronic design, a semiconductor intellectual property core (SIP core), IP core, or IP block is a reusable unit of logic, cell, or integrated circuit layout design that is the intellectual property of one party. IP cores can be licensed to ...

s, or some combination of all three. It produces an IC layout that is automatically converted to a

mask work Layout designs (topographies) of integrated circuits are a field in the protection of intellectual property. In United States intellectual property law, a "mask work" is a two or three-dimensional layout or topography of an integrated circuit ...

in the standard GDS II or the

OASIS In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.” The location of oases has been of critical imp ...

format.A. Kahng, J. Lienig, I. Markov, J. Hu: "VLSI Physical Design: From Graph Partitioning to Timing Closure", Springer (2011), , , pp. 7-11.

History

The final layout of early ICs and PCBs was stored as a

tape-out In electronics and photonics design, tape-out or tapeout is the final result of the design process for integrated circuits or printed circuit boards before they are sent for manufacturing. The tapeout is specifically the point at which the graphic ...

Rubylith image:Rubylith two rolls 2012.jpg, 200px, Rolls of lithographer's tape (these rolls are made by 3M). The roll in the back is 1/4 inch, the one in the front, 1/2 inch width. These products are often called "Rubylith" tape because Rubylith has become ...

on transparent film. Gradually,

automated more and more of the place-and-route work. At first, it merely sped up the process of making many small edits without spending a lot of time peeling up and sticking down the tape. Later

design rule checking In electronic design automation, a design rule is a geometric constraint imposed on circuit board, semiconductor device, and integrated circuit (IC) designers to ensure their designs function properly, reliably, and can be produced with acceptabl ...

sped up the process of checking for the most common sorts of errors. Later auto routers speed up the process of routing. Some people hope that further improvements in autoplacers and autorouters will eventually produce good layouts without any human manual intervention. Further automation leads to the idea of a

silicon compiler A silicon compiler is a software system that takes a user's specifications and automatically generates an integrated circuit (IC). The process is sometimes referred to as hardware compilation. Silicon compilation takes place in three major steps ...

References

{{Digital electronics Electronic design automation