[ekiwi]

Chisel imho solves the "synthesizable subset" problem quite elegantly: All Chisel constructs are simple, synthesizable circuit elements and boolean functions (+ functions on fixed size integers that can be converted into boolean functions). All automation happens in the meta-language which in this case is Scala. Chisel was always intended for synthesizable hardware!

[Rochus]

Scala is a general purpose programming language. Chisel is therefore it's "synthesizable subset". To use Chisel you need to know Scala as well as the HW design specific constructs Chisel offers.

EDIT: and Scala or the functional programming paradigm are not something design or verifications engineers are usually familiar with, which was apparently also a major issue in the Google project according to the referenced talk (quote: "frankly, most hardware engineers don't really get passed this yellow [Chisel learning] curve")

[ekiwi]

> Chisel is therefore it's "synthesizable subset".

Chisel is not synthesizing Scala. It is just a library implemented in Scala that allows you to create a data structure that describes a circuit.

Something like:

  circuit = Circuit("test")
  module = circuit.module("test")
  in0 = module.input("in0")
  // ...

The one thing Chisel adds on top of an Object hierarchy that describes a circuit is what PL people normally call "syntactic sugar". I.e., Chisel makes constructing this circuit object look more like a Verilog circuit by taking advantage of some nice Scala features. However, in the background, we are just constructing a data structure that represents a circuit, just like in a GUI library you might construct a data structure that describes your widget hierarchy. Chisel is not High Level Synthesis.

[Rochus]

> Chisel is not synthesizing Scala

Obviously I neither wrote nor meant that.

[monocasa]

What I think the other user is getting at is that Chisel isn't a "synthesizable subset" of Scala. You can use any Scala you want as Chisel is just a library. The model isn't a subset of Scala that can be turned into a netlist with the right compiler, but of a library for metaprogramming netlist graphs.