Place and route (also called PnR or P&R) is a stage in the design of

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

s, integrated circuits, and field-programmable gate arrays. 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 theory, 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 ...

. The first step, placement, involves deciding where to place all electronic components, circuitry, and

logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...

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 called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

s, during which components are graphically placed on the board and the wires drawn between them *

Integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

s, during which a

layout In general terms, a layout is a structured arrangement of items within certain limits, or a plan for such arrangement. Specifically, layout may refer to: * Page layout, the arrangement of visual elements on a page ** Comprehensive layout (comp), ...

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

. 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 A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

s, and their signal integrity needs may require optimization of the placement. The resulting design is then output in RS-274X Gerber format to load in the computer-aided manufacturing (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 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, usually to design application-specific integrated circuits (ASICs) and to progra ...

such as

VHDL VHDL (Very High Speed Integrated Circuit Program, VHSIC Hardware Description Language) is a hardware description language that can model the behavior and structure of Digital electronics, digital systems at multiple levels of abstraction, ran ...

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, with the highest level of abstraction being at the re ...

. 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 cores, or some combination of all three. It produces an IC layout that is automatically converted to a mask work in the standard GDS II or the

OASIS In ecology, an oasis (; : oases ) is a fertile area of a desert or semi-desert environment

History

The final layout of early ICs and PCBs was stored as a tape-out of Rubylith 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 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 an electronic design automation software system, software tool that is used for high-level synthesis of integrated circuits. Such a tool takes a user's specification of an Integrated circuit design, IC design as input and auto ...

References

{{Digital electronics Electronic design automation