Chisel (an acronym for Constructing Hardware in a Scala Embedded Language) is an open-source hardware description language (HDL) used to describe digital electronics and circuits at the register-transfer level.
Chisel is based on Scala as a domain-specific language (DSL). Chisel inherits the object-oriented and functional programming aspects of Scala for describing digital hardware. Using Scala as a basis allows describing circuit generators. High quality, free access documentation exists in several languages.
Circuits described in Chisel can be converted to a description in Verilog for synthesis and simulation.
A simple example describing an adder circuit and showing the organization of components in Module with input and output ports:
A 32-bit register with a reset value of 0:
A multiplexer is part of the Chisel library:
Although Chisel is not yet a mainstream hardware description language, it has been explored by several companies and institutions. The most prominent use of Chisel is an implementation of the RISC-V instruction set, the open-source Rocket chip. Chisel is mentioned by the Defense Advanced Research Projects Agency (DARPA) as a technology to improve the efficiency of electronic design, where smaller design teams do larger designs. Google has used Chisel to develop a Tensor Processing Unit for edge computing. Some developers prefer Chisel as it requires one-fifth as much code and is much faster to develop than Verilog.
Circuits described in Chisel can be converted to a description in Verilog for synthesis and simulation using a program named FIRRTL.