Fold is an experimental language and compiler for synthesis of digital circuits at a high level of abstraction. It is intended to be flexible and to support wide range of applications with predictable synthesis results.
Some features:
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Users input high level description of the desired behavior in the form of a program. This program resembles C syntax in its form, supports variables of arbitrary bitwidth, and has arithmetic operators with sizing rules such that the operators never overflow.
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Choice of architecture is up to the user and does not involve heuristics. Users annotate the program through special syntax and statements to influence the architecture.
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The model for compilation of the program to logic generalizes both automatic pipelining and automatic compilation of finite state machines.
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As a debugging aid, the programmatic description in Fold can be compiled into machine code to be executed as an ordinary computer program. The Fold toolchain provides certain guarantees about the matching behavior of the compiled machine code and the compiled logic.
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Logic compiler integrates into Yosys. Produced netlist is in the Yosys' RTLIL format, can be exported to Verilog.
See the Quick Start document.
Be welcome to join the Matrix room (hosted on gitter.im) to discuss the project and ask any questions.
The Fold logic compiler spans a frontend written in Python and a sequence of circuit processing passes written in C++. As a whole the compiler depends on Yosys with the Python binding (ENABLE_PYOSYS := 1 build option of Yosys). To build the circuit processing passes, run make in the root of the repository. This will produce a Yosys plugin binary at build/fold.so. Yosys 0.35 at the minimum is required.
The logic compiler can be invoked with
python -m fold.logic
in the root of the repository. It will automatically load the binary plugin. Pass -h to see help with command line usage.
The machine code compiler is written purely in Python, depends on llvmlite, and is invoked with
python -m fold.machinecode
To build a Fold program sample.fold into an RTLIL netlist sample.il:
python -m fold.logic -o sample.il sample.fold
To simulate the program, supplying implementations for the MUTEX_ASSERT debugging cells that will be part of the netlist:
yosys -p "read_rtlil sample.il; read_verilog -sv support/mutex_assert.sv; hierarchy -top top; proc; memory_nordff; sim -clock clk -reset rst"
There's optional "ExecID" instrumentation that needs to be enabled for checking that the memory accesses in logic implementation respect program order. This "ExecID" instrumentation has the form of a circuit of cells with types which are prefixed with EXECID_. As of now these cells don't have an implementation apart from a very limited one. If you run into one of the limitations the cells trigger a failed assert.
Even this limited implementation serves to demonstrate the principle, and is a placeholder for a full-fledged implementation in the future.
To build a Fold program sample.fold into an RTLIL netlist sample.il including the ExecID instrumentation:
python -m fold.logic --execid -o sample.il sample.fold
To simulate the program, supplying implementations for the MUTEX_ASSERT debugging cells that will be part of the netlist, and also supplying a limited implementation for the ExecID cells:
yosys -p "read_rtlil sample.il; read_verilog -sv support/mutex_assert.sv support/dummy_execid.sv; hierarchy -top top; proc; memory_nordff; sim -clock clk -reset rst"
This work is distributed under the terms of the ISC license, see the copyright notice and the license text below.
Copyright 2023 Martin Povišer <povik@cutebit.org>
Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.
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