Calyx | A Compiler Infrastructure for Accelerator Generators

Frontends

Dahlia »

Dahlia is an imperative, loop-based programming language for generating hardware accelerators.

Systolic Array »

Systolic arrays are the class of architectures that power AI chips like Google's TPUs.

TVM »

TVM is a compiler for machine learning frameworks that can optimize and target kernels to several different backends.

Language

Components

Components are the basic building block of Calyx programs. A component has three sections: cells, wires, and control. An empty component does nothing.

component main() -> () {
  cells { }
  wires { }
  control { }
}

Cells

The cells section instantiates sub-components like adders and registers. These sub-components can be used in this component to define behaviour.

component main() -> () {
  cells {
    // A 32-bit register
    c = std_reg(32);
  }
  wires { }
  control { }
}

Assignments & Guards

The wires section specifies connections to cells. They are continuously active by default and work like non-blocking assignments in RTL.

Guarded assignments have a boolean expression that controls when the assignment should be active.

component main() -> () {
  cells {
    // A 1-bit register
    b = std_reg(1);
    // A 32-bit register
    c = std_reg(32);
  }
  wires {
    // write a 1-bit constant to b
    b.in = 1'd1;
    b.write_en = 1'd1;

    // write 1 when b.out == 1
    c.in = b.out ? 32'd1;
    // write 2 when b.out == 0
    c.in = !b.out ? 32'd2;
  }
  control { }
}

Groups

A group is a collection of assignments that are only active when the group is run from the control program. The write_c[done] port is a special port defined on groups that signify when the group has finished.

component main() -> () {
  cells {
    // A 32-bit register
    c = std_reg(32);
  }
  wires {
    group write_c {
      c.in = 32'd1;
      c.write_en = 1'd1;
      // group is done when reg is done
      write_c[done] = c.done;
    }
  }
  control { }
}

Control

The control language specifies the order to run groups. The language has the normal imperative control flow operators: seq, if, and while. It also has par to express parallel composition.

component main() -> () {
  cells {
    a = std_reg(32);
    b = std_reg(32);
  }
  wires {
    group write_a { ... }
    group read_a { ... }
    group write_b { ... }
  }
  control {
    seq {
      write_a;
      par {
        read_a;
        write_b;
      }
    }
  }
}