Place and route
Encyclopedia
Place and route is a stage in the design of printed circuit board
s, integrated circuits, and field-programmable gate array
s. As implied by the name, it is composed of two steps, placement
and routing. The first step, placement, involves deciding where to place all electronic components, circuitry, and logic
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:
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
(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.
and generation of a netlist
. The generated netlist is then read into a layout tool and associated with part footprints from a library. Placing and routing can now start.
Placing and routing is generally done in two steps. Placing
the components comes first, then routing
the connections between the components. The component placement 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
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 CAM system of the manufactures
Hardware Description Language
(VHDL), or Verilog
. 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.
of Rubylith
on transparent film
.
Gradually, electronic design automation
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
.
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s, integrated circuits, and field-programmable gate array
Field-programmable gate array
A field-programmable gate array is an integrated circuit designed to be configured by the customer or designer after manufacturing—hence "field-programmable"...
s. As implied by the name, it is composed of two steps, placement
Placement (EDA)
Placement is an essential step in electronic design automation - the portion of the physical design flow that assigns exact locations for various circuitcomponents within the chip’s core area...
and routing. The first step, placement, involves deciding where to place all electronic components, circuitry, and logic
Logic
In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
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 boardPrinted circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s, during which componentElectronic componentAn electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...
s are graphically placed on the board and the wires drawn between them - Integrated circuitIntegrated circuitAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s, during which a layoutIntegrated circuit layoutIntegrated circuit layout, also known IC layout, IC mask layout, or mask design, is the representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal, oxide, or semiconductor layers that make up the components of the integrated circuit.When...
of a larger block of the circuit or the whole circuit is created from layouts of smaller sub-blocks - FPGAs, during which logicLogicIn philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
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
Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...
(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 schematicCircuit diagram
A circuit diagram is a simplified conventional graphical representation of an electrical circuit...
and generation of a netlist
Netlist
The word netlist can be used in several different contexts, but perhaps the most popular is in the field of electronic design. In this context, a "netlist" describes the connectivity of an electronic design....
. The generated netlist is then read into a layout tool and associated with part footprints from a library. Placing and routing can now start.
Placing and routing is generally done in two steps. Placing
Placement (EDA)
Placement is an essential step in electronic design automation - the portion of the physical design flow that assigns exact locations for various circuitcomponents within the chip’s core area...
the components comes first, then routing
Routing (EDA)
In electronic design, wire routing, commonly called simply routing, is a step in the design of printed circuit boards and integrated circuits . It builds on a preceding step, called placement, which determines the location of each active element of an IC or component on a PCB...
the connections between the components. The component placement 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
Signal (electrical engineering)
In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying or spatial-varying quantity....
s, and their signal integrity
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 waveform. However, digital signals are fundamentally analog in nature, and all signals are subject to effects such as noise,...
needs may require optimization of the placement.
The resulting design is then output in RS-274X Gerber format to load in the CAM system of the manufactures
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. The FPGA is designed using logic diagrams containing both digital logic and Very High Speed Integrated CircuitsVHSIC
VHSIC was a 1980s U.S. government program to develop very-high-speed integrated circuits.The United States Department of Defense launched the VHSIC project in 1980 as a joint tri-service project. The project led to advances in integrated circuit materials, lithography, packaging, testing, and...
Hardware Description Language
Hardware description language
In electronics, a hardware description language or HDL is any language from a class of computer languages, specification languages, or modeling languages for formal description and design of electronic circuits, and most-commonly, digital logic...
(VHDL), or Verilog
Verilog
In the semiconductor and electronic design industry, Verilog is a hardware description language used to model electronic systems. Verilog HDL, not to be confused with VHDL , is most commonly used in the design, verification, and implementation of digital logic chips at the register-transfer level...
. 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 Stream Format.History
The final layout of early ICs and PCBs was stored as a tape-outTape-out
In electronics design, tape-out or tapeout is the final result of the design cycle for integrated circuits or printed circuit boards, the point at which the artwork for the photomask of a circuit is sent for manufacture....
of Rubylith
Rubylith
Rubylith is a brand of masking film, invented and trademarked by the Ulano Corporation. Today the brand has become genericized to the point that it has become synonymous with all coloured masking films....
on transparent film
Transparency (projection)
A transparency, also known in industrial settings as a "viewfoil" or "foil", is a thin sheet of transparent flexible material, typically cellulose acetate, onto which figures can be drawn. These are then placed on an overhead projector for display to an audience...
.
Gradually, electronic design automation
Electronic design automation
Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...
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
Design rule checking
Design Rule Checking or Check is the area of Electronic Design Automation that determines whether the physical layout of a particular chip layout satisfies a series of recommended parameters called Design Rules...
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
Silicon compiler
A silicon compiler is a software system that takes a user's specifications and automatically generates an integrated circuit . The process is sometimes referred to as hardware compilation.Silicon compilation takes place in three major steps:...
.