7. C HLS frontend

SiliconCompiler supports high-level synthesis of C code to any supported SC target, implemented using the Bambu HLS tool. To get started compiling C code with SC, ensure that SC is installed following the directions from the Installation section, and build Bambu from source following the instructions here. For Ubuntu 20.04, we’ve additionally provided a setup script.

To build a C design, the only things you need to do differently from a configuration perspective are:

  1. Add all required C files as inputs.

  2. Set the ['option', 'frontend'] parameter to ‘c’.

Otherwise, you can configure the build as normal.

For example, to implement a GCD function as a circuit, first copy the following into a file called “gcd.c”.

#include <stdio.h>

short gcd(short a, short b) {
    if (b > a) {
        short tmp = a;
        a = b;
        b = tmp;
    }

    while (a != 0 && b != 0) {
        short r = a % b;
        a = b;
        b = r;
    }

    if (a == 0)
        return b;
    else
        return a;
}

int main() {
    printf("gcd(4, 4) = %d\n", gcd(4, 4));
    printf("gcd(27, 36) = %d\n", gcd(27, 36));
    printf("gcd(270, 192) = %d\n", gcd(270, 192));

    return 0;
}

Note

SC’s C frontend driver script selects a function to implement as a Verilog module using the ‘design’ parameter. Ensure that your C code includes a function that matches the value stored in ‘design’.

This design can then be quickly compiled to a GDS using the command line:

sc gcd.c -frontend c
sc-show -design gcd

Or using Python:

import siliconcompiler

def main():
    chip = siliconcompiler.Chip('gcd')
    chip.set('input', 'c', 'gcd.c')
    chip.set('option', 'frontend', 'c')
    # default Bambu clock pin is 'clock'
    chip.clock(pin='clock', period=5)
    chip.load_target('freepdk45_demo')
    chip.run()
    chip.summary()
    chip.show()

if __name__ == '__main__':
    main()

For more information on the Bambu project used for implementing this frontend, see their docs.