HLS Expression forms: Behavioural using a Thread or Threads

We express the algorithm and steps to be performed as an executable program

• using an imperative program (containing loops and assigments), or
• a functional program (where control flow is less-explicit).

Either way, the tool chain may:

• re-order the operations while preserving semantics, and/or
• re-encode the state and modify memory layouts.

Examples:

• Hardware Construction Languages (Lava, Chisel 2.0),
• Synopsys Behavioural Compiler for RTL (now defunct),
• Classical HLS: C-to-Gates : C-To-Verilog, SystemCrafter, LegUp, Catapult,
• Bluespec's Imerative (FSM) sublanguage,
• Handel-C (based on OCCAM),
• Object oriented: Liquid Metal (Lime Language, IBM), Kiwi (Univ Cambridge/Microsoft),
• Using Join Patterns or other parallel process algebra (C-omega).

The Kiwi, C-omega and Handel-C approaches start with parallel programs and exploit the scheduler non-determinacy to allow variations in implementation.