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# Glossary
```{glossary}
:sorted:
IPVT
Short for Interconnect, Process, Voltage, and Temperature, the four
components of a {term}`timing corner` in LibreLane.
timing corner
A set of simulated physical conditions under which timing analysis is
performed.
[Nix](https://nixos.org)
A declarative build utility that can be used to create development
environments in a pure and reproducible manner for both Linux and macOS.
LibreLane environments including tools are built with Nix.
[sky130](https://github.com/google/skywater-pdk)
The SkyWater Open Source {term}`PDK` is a collaboration between Google, Efabless and
SkyWater Technology Foundry to provide a fully {term}`open-source` PDK and
related resources, which can be used to create manufacturable designs at
SkyWater’s facilities. sky130 is a mature 180nm-130nm hybrid technology
originally developed internally by Cypress Semiconductor before being spun
out into SkyWater Technology and made accessible to general industry.
sky130 is the default PDK for use with LibreLane as it was the first entirely
open-source PDK.
PDK
Short for Process Design Kit.
A set of files used within the
semiconductor industry to model a fabrication process for the design
tools used to design an integrated circuit.
RTL
Short for Register-Transfer Level.
An abstraction used in {term}`HDL`s like Verilog
and VHDL to create high-level representations of a circuit, from which
lower-level representations and ultimately actual wiring can be derived.
Design at the RTL level is typical practice in modern digital design.
Netlist
A representation of the circuit modeling pre-hardened elements (standard
cells and macros) and the connections between them.
In LibreLane, Netlists can be in Verilog, in which case they are
**gate-level netlists** that model cells in ideal conditions and are only
interested in verifying the logical correctness of the circuit, or they can
be {term}`SPICE netlist`(s), which model down to the transistor level and
can simulate various physical conditions.
GDSII
Short for Graphic Design System II.
A binary stream format which is the *de facto* industry standard for data
exchange of integrated circuit or IC layout artwork. It was developed by
Calma Company in 1978. A GDSII file contains planar geometric shapes, text
labels, and other information about the layout in hierarchical form. The
data can be used to reconstruct all or part of the artwork to be used in
sharing layouts, transferring artwork between different tools, or creating
photomasks. It captures all the layout details needed by the manufacturer.
GDSII was once the standard for {term}`tape-out`, but it has since been
replaced by OASIS, a more compact storage format. LibreLane uses GDSII as
it has better open-source tool support, but shuttle providers would broadly
request the data to be converted to OASIS. {term}`KLayout` is an open-source
tool capable of performing the conversion.
[KLayout](https://www.klayout.de/)
A free and {term}`open-source` layout ({term}`DEF`/{term}`GDSII`) viewer and
editor.
PnR
Short for placement and routing.
A phase of digital circuit implementation where:
1. the positions of standard cells and macros within a layout are
determined and checked for legality (placement)
2. the shapes of the physical connections between those cells are determined
and also checked for legality (routing)
[OpenROAD](https://openroad.readthedocs.io/en/latest/)
An {term}`open-source` tool chain for digital SoC layout generation,
focusing on the RTL-to-GDSII phase of system-on-chip design. It is used for
floorplanning, {term}`PnR` and design optimizations inside LibreLane.
[OpenLane](https://github.com/The-OpenROAD-Project/OpenLane)
The progenitor of LibreLane, OpenLane is an ASIC flow developed by Efabless
Corporation in 2020 for use with the Google {term}`OpenMPW` project.
OpenLane focused on ease of installation and ease of use by including all
tools and allowing the users to configure the entire ASIC flow using one
Tcl or JSON file.
[Magic](http://opencircuitdesign.com/netgen)
A free software layout ({term}`DEF`/{term}`GDSII`) viewer and editor.
[Yosys](https://github.com/YosysHQ/yosys)
A framework for RTL synthesis tools with extensive Verilog-2005 support.
SDC
Stands for Synopsys® Design Constraints.
A Tcl-based format used to describe design requirements including timing,
power, and area to EDA tools. Supports of a subset of the Tcl commands
provided by timing tools.
Tcl
A shell language popular for embedded interpreter inside {term}`EDA`
tools, initially designed by John Osterhout for use with the {term}`Magic`
VLSI tool.
{term}`Yosys`, {term}`OpenROAD` and {term}`Magic` are all Tcl-programmable,
in addition to most proprietary electronic design automation tool. LibreLane
accepts design configuration files in the Tcl format as previous versions of
LibreLane were written in Tcl.
metrics
Quantitative measures representing physical characteristics of a design.
Typically, these include values like the area of the design, worst clock
slack, average voltage drop, et cetera, but in LibreLane the conventional definition
is expanded to include any and all information about the circuit generated
during runtime, encompassing things such as lint violations in the
{term}`RTL` description of the circuit, the number of pins, et cetera.
[METRICS2.1](https://github.com/ieee-ceda-datc/datc-rdf-Metrics4ML#metrics21-naming-convention)
A naming convention for {term}`metrics` of a design used by {term}`OpenROAD`
and LibreLane. LibreLane is responsible for extracting and naming metrics
in a 2.1-compliant format from tools other than OpenROAD.
LEF
Short for "Layout Exchange Format".
An abstract view of pre-hardened macros and standard cells, containing
information about the cell's dimensions, pin positions and elements on
metal layers.
The LEF language is defined in the {term}`LEFDEFREF`.
DEF
Short for "Design Exchange Format".
An abstract view of the current working design, listing instantiated cells
and macros as well as any elements on metal layers, including pins.
When a design is hardened, {term}`LEF` and {term}`GDSII` views are
generated from the DEF view.
The DEF language is defined in the {term}`LEFDEFREF`.
LEFDEFREF
Refers to the LEF/DEF Language Reference by Cadence
Inc.
The LEFDEFREF is obtainable for free from Silicon Integration Initiative,
Inc.'s
[Complimentary OpenAccess Tools, Libraries, and Utilities](https://si2.org/oa-tools-utils-libs/).
As of the time of writing, a slightly out of date but still valid version is
also available from the
[ISPD's 2018 detailed routing contest downloads](https://www.ispd.cc/contests/18/lefdefref.pdf).
CSV
Short for "Comma-separated Values".
A text file that represents tabular data.
JSON
Short for JavaScript Object Notation.
A data interchange format derived from JavaScript supporting numeric, Boolean
and string values as well as lists and hashmaps composed of the above.
LibreLane uses JSON as the primary form for loading and storing configuration
data.
Verilog
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 (RTL) of abstraction.
[Netgen](http://opencircuitdesign.com/netgen)
A {term}`open-source` tool for running {term}`LVS`.
SPICE
Short for Simulation Program with Integrated Circuit Emphasis.
A public-domain utility for simulating analog circuits. Unlike (most)
Verilog simulators, SPICE enables the simulation of a variety of physical
conditions of a circuit, including but not limited to, temperature,
extracted parasitic resistances and capacitances, transistor switching
speed, and so on.
SPICE itself is not part of any included LibreLane flows, but
{term}`SPICE netlist`s are.
SPICE netlist
A netlist readable by {term}`SPICE` and compatible utilities. Unlike Verilog
netlists, SPICE netlists are capable of capturing an analog view of the
circuit.
By comparing the digital Verilog netlist and analog SPICE netlist, LibreLane
performs {term}`LVS`.
ASIC
Short for Application-Specific Integrated Circuit.
As the name implies, it is silicon that is manufactured to execute a specific
function (even though these functions may be themselves generic, i.e., a
CPU is an ASIC that performs general-purpose computing).
Broadly, digital design targets one of two technologies: ASIC manufacturing
(higher upfront cost but lower-cost scaling) or {term}`FPGA` (lower-cost
upfront cost but *very* costly scaling.)
LibreLane flows primarily target ASIC technologies for manufacturing.
FPGA
Short for Field-Programmable Gate Array.
An integrated circuit that can be reprogrammed to perform various digital
functions much, much faster than a general-purpose computer, but at a
recurring cost, area and performance penalty compared to a dedicated ASIC.
Popular for prototyping ASICs or for niche applications where the upfront
cost of an ASIC is not financially justifiable.
EDA
Short for Electronic Design Automation.
A field concerned with the development software, hardware, and services to
enable the automation of chip design tasks. LibreLane and all of its
constituent utilities could be considered EDA tools.
foundry
A semiconductor manufacturer, such as GlobalFoundries, SkyWater Technologies,
or TSMC.
process node
A semiconductor manufacturing process executed by a certain chip foundry,
typically identified by the foundry name and a number, i.e., the Skywater
130 nm process ({term}`sky130`).
Historically, the process node number used to refer to a physical characteristic
of the circuit such as the minimum feature length, but since the mid-1990s,
the number has become more or less arbitrary.
To create a design to be manufactured on a particular process node, a
{term}`process design kit <PDK>` for that node is required.
DRC
Short for Design Rule Checks.
Rules set by a chip foundry for a certain chip manufacturing process that
broadly have to be satisfied by a design for a design to be actually
manufacturable.
A design that does not have any DRC violations is referred to as DRC-clean.
LVS
Short for Layout vs. Schematic.
A comparison between the engineering schematic for a certain design (abstract)
and its (concrete) physical layout. This catches misconfigured power connections
or bugs with {term}`PnR` tools.
A design that does not have any LVS errors is referred to as LVS-clean.
DRC deck
An implementation of a set of {term}`DRC`s for a certain utility.
On-chip variation
Variations in physical and electrical characteristics of chips. They can
occur due to factors such as manufacturing processes, material properties,
or environmental conditions.
Sometimes abbreviated as OCV.
STA
Short for Static Timing Analysis.
A method for determining the validity of a chip's timing parameters without
performing a full functional simulation thereof.
A chip for which STA reveals no timing constraint violations is said to
have achieved {term}`timing closure`.
timing closure
A term given for designs for which STA has revealed that there exist no
violations of timing constraints at a certain clock period and at all
{term}`timing corners <timing corner>`.
Designs that have not achieved timing closure are usually not suitable
for {term}`tape-out`.
IEEE
Short for the Institute of Electrical and Electronics Engineers.
A professional association for electronics and electrical engineers. IEEE
sets the standard for a number of formats in the EDA space, including
the Verilog Hardware Description Language.
SPEF
Short for Standard Parasitic Exchange Format.
An {term}`IEEE` standard for representing parasitic resistances and
capacitances of wires in a circuit.
SDF
Short for Standard Delay Format.
An {term}`IEEE` standard for representing and interpreting timing data for
use at any stage of an electronic design process.
open-source
A model for releasing products where upon the source files are also made
available for free (as in free spreech, not necessarily but usually
also free of cost) modification and redistribution.
The term is more accurately defined by the Open Source Initiative (OSI) at
this link: https://opensource.org/osd
Caravel
A test harness initially released by Efabless Corporation for use with
the {term}`OpenMPW` and [chipIgnite](https://chipfoundry.io/chipignite)
programs, that enforces a common pinout for all user projects as well as
providing a number of base functions, including a management SoC, I/O
configuration, power, clocking, and more.
See https://caravel-harness.readthedocs.io/en/latest/ for more info.
OpenMPW
A lapsed program by Google sponsoring a free Multi-Project Wafer for
{term}`open-source` hardware projects.
LibreLane's progenitor, {term}`OpenLane`, was initially developed for use
with the OpenMPW project.
See https://developers.google.com/silicon for more info.
MPW
Short for Multi-Project Wafer.
A wafer produced aggregating a number of different chips, allowing the cost
of a wafer to be spread across multiple projects.
{term}`OpenMPW` is an example of a Multi-Project Wafer shuttle.
dotlib
Also `.lib`.
A library format for macros including standard cells, modeling at an
abstract level the interface to and timing properties of a cell.
Typically used for Synthesis and {term}`STA`.
Gzip
A free and open-source compression format. A great many number of tools
support Gzipped inputs transparently, i.e., any file beginning with the
bytes `1f 8b` is automatically decompressed without any special input
from the user.
Gzipping is popular for text-heavy formats such as {term}`dotlib` or
{term}`SPEF` formats.
HDL
Short for "Hardware Description Language."
A computer language used to, quite literally, describe the structure or
behavior of a hardware chip. The most famous of which is Verilog.
HDLs can model hardware at various levels of abstraction, from listing every
single gate used in the design ({term}`gate-level netlist <netlist>`) to
more abstract behavioral models ({term}`register transfer level <RTL>`).
A synthesis tool is used to transform the abstract behavioral models into
concrete netlists.
The most famous hardware description languages are {term}`Verilog` and VHDL.
tape-out
The final stage of IC design, after all checks have concluded. The design
is sent to a fabrication facility where the masks are then made from the
{term}`GDSII` or compatible format.
The name tape-out is a historical artifact from when the GDSII streams were
quite literally submitted to the foundries on tape. Nowadays files are
typically uploaded using something like an FTP server, but the term stuck.
ECO
Short for Engineering Change Order.
Used as a catch-all term for manual modifications of netlists that have been
processed by tools. Can be used for last-minute physical or timing violation
fixes and/or logical fixes.
```
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