HLS Synthesisable Subset.

Can we convert arbitrary or legacy programs to hardware ? Not very well in general.

Can we write new HLL programs that compile to good hardware ? Yes. But we must stick to the supported subset for synthesis.

Typical HLS restrictions:

• Program must be finite-state and single-threaded,
• all recursion bounded,
• all dynamic storage allocation outside of infinite loops (or deallocated again in same loop),
• use only boolean logic and integer arithmetic,
• limited string handling,
• very-limited standard library support,
• be explicit over which loops have run-time bounds.

An early example » DJG C-To-V compiler from 1995. » Bubble Sorter Example

Today many commercial HLS tools are widely available: SystemCrafter, Calypto Catapult, SimVision, CoCentric, C-Level Design, Forte Cynthesizer (now acquired by Cadence), C-to-Verilog.com and xPilot now called Vivado HLS, ... other tools are/were HardwareC, SpecC, Impulse-C, NEC Cyber Workbench, Synopsis SynphonyC.

And research HLS tools, such as Kiwi and LegUp, support floating point, pointers and some dynamic storage allocation using DRAM banks as necessary,