gsvgit / heron

A special-purpose processor for pure, non-strict functional languages

Heron Core

Being a compiler, emulator, and hardware description for Heron --- a special purpose processor core for pure, non-strict functional languages.

We consider this a spiritual successor to the Reduceron project, extending their ideas around FPGA implementation of a template instantiation machine. The bulk of the compiler is a modified version of their F-lite compiler, while the hardware description is completely reimplemented in Clash.

Building

We package all components in a single nix flake. If you have nix installed, nix flakes enabled, and Xilinx Vivado on your PATH, the nix environment here will configure everything else needed.

Clone this repo and then use nix build to reproduce any of Heron's components:

• F-lite compiler --- a translator from the high-level source language, F-lite, to Heron graph templates. The output binaries will be linked in the result/ folder.

  nix build .#flite

• Heron emulator --- a "fast" emulation of the hardware behaviour, implemented in C. This is an extension of Reduceron's emulator. Usually you'd want both of the above (maybe nix shell -p .#flite .#heron-emu) so you can compile an F-lite program and then emulate the resulting template representation.

  nix build .#heron-emu

• Heron hardware description written in Clash. This is a (compile-time) parameterised description of the sequential Heron Core processor. The build process generates a Verilog netlist for the core, which can then be implemented via the board-specific heron-alveo or heron-ultra96 targets.

  nix build .#heron-clash

• An implementation of Heron for the Alveo U280 board. Currently a raw design with pins exposed via device IOBs. Since this relies on Vivado for synthesis and implementation, we need to use nix's --no-sandbox and --impure flags to allow the build environment access to a global Vivado install (make sure it's on your path before building...).

  nix build .#heron-alveo --no-sandbox --impure

• An alternative implementation of Heron for the Ultra96 board with interactivity via PYNQ. This is a much smaller/slower device, but the current implementation does offer software control for loading custom programs and retrieving results.

  nix build .#heron-ultra96 --no-sandbox --impure

All dependencies (except Vivado) are handled through nix, so feel free to jump straight to building heron-alveo.

Development

Normal nix flake rules apply for development. Enter a development environment for any build target with nix develop .#<target> (omitting the target will default to heron-clash). The target's commands for building, checking, and installing can be retrieved via the env variables buildPhase, checkPhase, or installPhase respectively. Both F-lite and heron-clash are packaged as cabal packages under the nix hood. You might find the standard cabal commands easier for interactive development once in a development environment. For example:

user@pc:~/heron$ nix develop .#heron-clash
user@pc:~/heron$ cabal repl heron
ghci> :l Heron.Core.Board
ghci>

We can perform testing with cd hdl; cabal test, or generate documentation with cd hdl; cabal haddock.

License

Our project license is currently GPL 2.0. See LICENSE for details.