Glossary — Project Trellis documentation

# Glossary

Arc

  A programmable connection between two nodes. Most arcs are unidirectional buffers that connect in one direction only, a few are bidirectional switch transistors (however these are mostly used in situations where this is one useful direction anyway).

ASIC

  An application-specific integrated circuit (ASIC) is a chip that is designed and used for a specific purpose, such as video acceleration, machine learning acceleration, and many more purposes. In contrast to FPGAs, the programming of an ASIC is fixed at the time of manufacture.

Bitstream

  Binary data that is directly loaded into an FPGA to perform configuration. Contains configuration frames as well as programming sequences and other commands required to load and activate same.

Database

  Contains information about programmable configuration bits, arc enable bits, and how wires are connected between tiles.

FF
Flip flop

  A flip flop (FF) is a logic element on the FPGA that stores state.

FPGA

  A field-programmable gate array (FPGA) is a reprogrammable integrated circuit, or chip. Reprogrammable means you can reconfigure the integrated circuit for different types of computing. You define the configuration via a hardware definition language (HDL). The word “field” in field-programmable gate array means the circuit is programmable in the field, as opposed to during chip manufacture.

Frame

  A frame contains a row of bits used to configure the FPGA, and is the basic unit that a bitstream is split into. The number of bits per frame, and frames per device varies for different ECP5 chips.

Fuzzer

  Scripts and a makefile to generate one or more specimens and then convert the data from those specimens into a database.

General Routing

  Routing that connects together nearby tiles horizontally or vertically, spanning up to about 15 tiles at most. Called “shortwires” in Lattice Diamond, but this also refers to internal routing.

Global Routing

  Routing that connects to all tiles in a quadrant for logic, and all tiles on an edge for IO. Normally used for routing clocks, or occasionally other high fanout signals. Called “longwires” in Lattice Diamond.

Half

  Portion of a device defined by a virtual line dividing the two sets of global clock buffers present in a device. The two halves are referred to as the top and bottom halves.

HDL

  You use a hardware definition language (HDL) to describe the behavior of an electronic circuit. Popular HDLs include Verilog (inspired by C) and VHDL (inspired by Ada).

Internal Routing

  Routing that does not leave a single tile.

LUT

  A lookup table (LUT) is a logic element on the FPGA. LUTs function as a ROM, apply combinatorial logic, and generate the output value for a given set of inputs.

MUX

  A multiplexer (MUX) is a multi-input, single-output switch controled by logic.

Node

  A routing node on the device. A node is a collection of wires spanning one or more tiles. Nodes that are local to a tile map 1:1 to a wire. A node that spans multiple tiles maps to multiple wires, one in each tile it spans.

PnR
Place and route

  Place and route (PnR) is the process of taking logic and placing it into hardware logic elements on the FPGA, and then routing the signals between the placed elements.

Quadrant

  The ECP5 FPGAs are arranged into four quadrants for the purpose of global signal distribution, upper left (UL), upper right (UR), lower left (LL) and lower right (LR).

Routing fabric

  The wires and programmable interconnects (arcs) connecting the logic blocks in an FPGA.

Site

  Locations inside a tile that can contain an instance of a primitive.

Specimen

  A bitstream of a (usually auto-generated) design with additional files containing information about the placed and routed design. These additional files are usually generated using programs included with Diamond to create debugging outputs.

Tile

  Fundamental unit of physical structure containing a single type of resource or function. The whole chip is a grid of tiles, however, multiple tiles may exist at one grid location.

Wire

  Physical wire within a tile.