Units

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

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.