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Cement: Streamlining FPGA Hardware Design with Cycle-Deterministic eHDL and Synthesis

Cement is a hardware design framework, which encompasses the embedded HDL (eHDL), CmtHDL and the compiler, CmtC, providing a better programming framework for FPGA. CmtHDL introduces event-based procedural specification alongside RTL description, empowering designers to describe hardware productively at a higher level of abstraction while maintaining cycle-deterministic behavior. CmtC provides a comprehensive compilation workflow that includes analyzing the timing behavior of the hardware and conducting synthesis to yield solutions with anticipated performance for FPGAs.

File Structure

|- Cement (Root of the repo)
  |- cement
    |- src
      |- hcl: CMTHDL's embedding
      |- compiler: CMTC's frontend
      |- gir: ir and passses for new-version state-tree-based control synthesis (WIP)
      |- std: basic primitives (WIP)
      |- simulator: pure-Rust simulator (WIP)
  |- cement_macros: macros for CMTHDL
  |- cement_examples: examples
  |- tgraph: graph representation and manipulation for control synthesis
  |- irony (also named ir-rs): CMTC backend
    |- irony: ir framework
    |- irony-cmt: ops and passes for CMTC

Usage

Setup

First, clone the repo.

git clone git@github.com:pku-liang/Cement.git

Then, initialize the submodules: irony for IR and passes, tgraph for control synthesis.

git submodule update --init

Now, use Cement by adding it as a dependency in your Cargo.toml as the cement_examples does.

[dependencies]
cmt = { path = <path-to-cement-directory> }

Examples

We provide examples under cement_examples/tsc/tests;

For example, cement_examples/src/tests/basics.rs contains a Pass::pass_m module and a TopPass::top_m module, where Pass and TopPass are types for module interfaces.

#[interface(Default)]
pub struct Pass {
  pub i: B<8>,
  pub o: Flip<B<8>>,
}

module! { Pass =>
    pass_m(module) {
        module.o %= module.i;
    }
}

#[interface(Default)]
pub(crate) struct TopPass {
  pass: Pass,
  i: B<8>,
  o: Flip<B<8>>,
}

module! { TopPass =>
    top_m(module) {
        let pass = instance!(pass_m(Pass::default()));
        let pass1 = instance!(pass_m(Pass::default()));
        module.pass %= pass;
        pass1.i %= module.i;
        module.o %= pass1.o + 1.lit(B8);
    }
}

#[test]
pub fn test_top_pass() -> Result<(), ()> {
  let mut c = Cmtc::new(CmtcConfig::default());
  TopPass::default().top_m(&mut c);
  c.print();
}

Then the test function test_top_pass print the produced CIRCT IR. The function can be run by the following command:

cargo test --package cement_examples --bin cement_examples -- tests::basics::test_top_pass  --exact --nocapture

If you want to look at the produced SystemVerilog, see cement_examples/src/tests/file_sys.rs, and run:

cargo test --package cement_examples --bin cement_examples -- tests::file_sys::test_fs --exact --nocapture 

Ongoing

The following features are under RECONSTRUCTION, and we will make them available as soon as they get ready:

• Control synthesis: working on a new control synthesis implementation based on the tgraph library.
• Exernal IPs or Verilog import
• Improve timing analysis

The reasons for the reconstruction include:

• The deprecated adhoc control synthesis implementation fails to guarentee the absense of extra cycles for some cases (especially for while loops) as required by the deterministic timing. We're working on a new implementation based on the tgraph library to resolve the issue and provide a more general and efficient control synthesis solution.
• The deprecated timing analysis fails to consider default values for wires and the reset situation, both of which are common cases in real-world designs. Besides, the sc functions are sets of enumerated cycles (too many!) for static analysis, and dynamic analysis generates too many assertions. We're working on an improved solution to cover the ignored cases and reduce analysis complexity.

We are also working on a Rust-based simulator (under cement/src/simulator) for CMTHDL designs.

Future Work

Any suggestions or discussions are welcomed. Please feel free to open an issue or contact us.

Paper

If you find this project useful in your research, please cite our paper that has been recently accepted to FPGA 2024:

@inproceedings{xiao2024cement,
  title={Cement: Streamlining FPGA Hardware Design with Cycle-Deterministic eHDL and Synthesis},
  author={Xiao, Youwei and Luo, Zizhang and Zhou, Kexing and Liang, Yun},
  booktitle={Proceedings of the 2024 ACM/SIGDA International Symposium on Field Programmable Gate Arrays (FPGA '24)},
  year={2024},
  address={Monterey, CA, USA},
  doi={10.1145/3626202.363756},
}