The Spade Hardware Description Language

Units

Units are the basic building blocks of a Spade project, they correspond to modules in Verilog, and entities in VHDL. In Spade units come in three flavors: functions, pipelines and entities.

You can see explicit examples of this in the guide-level documentation.

Functions

Functions are combinational circuits (or pure, in software terms), that is they have no internal state, and can not read or set mutable wires.

Pipelines

Pipelines have a specified delay between input and output, and have explicit staging statements.

Entities

Finally, entities are the most general units, they can have state, and the input-output delay is arbitrary. They therefore have roughly the same programming model as VHDL and Verilog.