slvcodec 0.4.1

Utilities for generating VHDL to convert to and from std_logic_vector, as well as utilties to create testbenches described by python.

slvcodec is a tool that analyzes VHDL and generates:

• Functions to convert arbitrary VHDL types to and from std_logic_vector.

• Generate testbenches for entities that read inputs from a file, and write outputs to a file.

• Utilities so that unit tests for VHDL code can easily to be written in python.

Generation of functions to convert to and from std_logic_vector

Here’s an example VHDL package.

library ieee;
use ieee.numeric_std.all;

package complex is

  constant FIXED_WIDTH: natural := 8;
  subtype fixed_t is unsigned(FIXED_WIDTH-1 downto 0);

  type complex_t is record
    real: fixed_t;
    imag: fixed_t;
  end record;

  type array_of_complex is array(natural range <>) of complex_t;

end package;

The following python script is used to generate a helper package that contains functions to convert the types to and from std_logic_vector.

import os

from slvcodec import filetestbench_generator


thisdir = os.path.dirname(__file__)


def make_slvcodec_package():
    complex_pkg_fn = os.path.join(thisdir, 'complex_pkg.vhd')
    directory = os.path.join(thisdir, 'generated')
    os.mkdir(directory)
    filetestbench_generator.add_slvcodec_files(directory, [complex_pkg_fn])


if __name__ == '__main__':
    make_slvcodec_package()

Here is what the generated VHDL looks like.

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use work.complex.all;
use work.slvcodec.all;

package complex_slvcodec is


  function to_slvcodec (constant data: array_of_complex) return std_logic_vector;
  function from_slvcodec (constant slv: std_logic_vector) return array_of_complex;
  constant fixed_t_slvcodecwidth: natural := fixed_width;
  constant complex_t_slvcodecwidth: natural := 2*fixed_width;
  function to_slvcodec (constant data: complex_t) return std_logic_vector;
  function from_slvcodec (constant slv: std_logic_vector) return complex_t;

end package;

package body complex_slvcodec is

  function to_slvcodec (constant data: array_of_complex) return std_logic_vector is
    constant W: natural := complex_t_slvcodecwidth;
    constant N: natural := data'length;
    variable slv: std_logic_vector(N*W-1 downto 0);
  begin
    for ii in 0 to N-1 loop
      slv((ii+1)*W-1 downto ii*W) := to_slvcodec(data(ii));
    end loop;
    return slv;
  end function;

  function from_slvcodec (constant slv: std_logic_vector) return array_of_complex is
    constant W: natural := complex_t_slvcodecwidth;
    constant N: natural := slv'length/W;
    variable mapped: std_logic_vector(slv'length-1 downto 0);
    variable output: array_of_complex(N-1 downto 0);
  begin
    mapped := slv;
    for ii in 0 to N-1 loop
      output(ii) := from_slvcodec(mapped((ii+1)*W-1 downto ii*W));
    end loop;
    return output;
  end function;

  function to_slvcodec (constant data: complex_t) return std_logic_vector is
    constant W0: natural := 0;
    constant W1: natural := W0 + fixed_width;
    constant W2: natural := W1 + fixed_width;
    variable slv: std_logic_vector(complex_t_slvcodecwidth-1 downto 0);
  begin
    slv(W1-1 downto W0) := to_slvcodec(data.real);
    slv(W2-1 downto W1) := to_slvcodec(data.imag);
    return slv;
  end function;

  function from_slvcodec (constant slv: std_logic_vector) return complex_t is
    constant W0: natural := 0;
    constant W1: natural := W0 + fixed_width;
    constant W2: natural := W1 + fixed_width;
    variable data: complex_t;
    variable mapped: std_logic_vector(complex_t_slvcodecwidth-1 downto 0);
  begin
    mapped := slv;
    data.real := from_slvcodec(mapped(W1-1 downto W0));
    data.imag := from_slvcodec(mapped(W2-1 downto W1));
    return data;
  end function;

end package body;

Generation of file-based testbenches

Here’s an example entity that just returns the magnitude squared of a complex data type that we defined earlier.

library ieee;
use ieee.numeric_std.all;
use work.complex.all;

entity complex_mag2 is
  port (
    i: in complex_t;
    o: out unsigned(FIXED_WIDTH+1-1 downto 0)
    );
end entity;

architecture arch of complex_mag2 is

  signal real2: signed(FIXED_WIDTH*2-1 downto 0);
  signal imag2: signed(FIXED_WIDTH*2-1 downto 0);
  signal mag2: unsigned(FIXED_WIDTH*2-1 downto 0);
  signal scaled_mag2: unsigned(FIXED_WIDTH+1-1 downto 0);

begin

  real2 <= i.real * i.real;
  imag2 <= i.imag * i.imag;
  mag2 <= unsigned(real2) + unsigned(imag2);

  scaled_mag2 <= mag2(FIXED_WIDTH*2-1-1 downto FIXED_WIDTH-2);

  o <= scaled_mag2;

end architecture;

We can use slvcodec to generate a testbench that reads input data from a file, and writes output data to another file.

import os

from slvcodec import filetestbench_generator


thisdir = os.path.dirname(__file__)


def make_slvcodec_package():
    complex_pkg_fn = os.path.join(thisdir, 'complex_pkg.vhd')
    directory = os.path.join(thisdir, 'generated')
    os.mkdir(directory)
    slvcodec_files = filetestbench_generator.add_slvcodec_files(directory, [complex_pkg_fn])
    return slvcodec_files


def make_complex_mag2_testbench():
    base_filenames = [
        os.path.join(thisdir, 'complex_pkg.vhd'),
        os.path.join(thisdir, 'complex_mag2.vhd'),
        ]
    slvcodec_fns = make_slvcodec_package()
    with_slvcodec_fns = base_filenames + slvcodec_fns
    directory = os.path.join(thisdir, 'generated')
    generated_fns, generated_wrapper_fns, resolved = filetestbench_generator.prepare_files(
        directory=directory, filenames=with_slvcodec_fns,
        top_entity='complex_mag2')
    return generated_fns


if __name__ == '__main__':
    make_complex_mag2_testbench()

This will generate the following VHDL testbench.

library ieee;
use ieee.std_logic_1164.all;
use work.slvcodec.all;
use ieee.numeric_std.all;
use work.complex.all;
use work.complex_slvcodec.all;

entity complex_mag2_tb is
  generic (

    CLOCK_PERIOD: time := 10 ns;
    RUNNER_CFG: string;
    OUTPUT_PATH: string
  );
end entity;

architecture arch of complex_mag2_tb is
  type t_input is
record
    i: complex_t;
end record;
type t_output is
record
    o: unsigned((1+fixed_width)-1 downto 0);
end record;
  constant t_input_slvcodecwidth: natural := 2*fixed_width;
  function to_slvcodec (constant data: t_input) return std_logic_vector;
  function from_slvcodec (constant slv: std_logic_vector) return t_input;
  function to_slvcodec (constant data: t_input) return std_logic_vector is
    constant W0: natural := 0;
    constant W1: natural := W0 + 2*fixed_width;
    variable slv: std_logic_vector(t_input_slvcodecwidth-1 downto 0);
  begin
    slv(W1-1 downto W0) := to_slvcodec(data.i);
    return slv;
  end function;

  function from_slvcodec (constant slv: std_logic_vector) return t_input is
    constant W0: natural := 0;
    constant W1: natural := W0 + 2*fixed_width;
    variable data: t_input;
    variable mapped: std_logic_vector(t_input_slvcodecwidth-1 downto 0);
  begin
    mapped := slv;
    data.i := from_slvcodec(mapped(W1-1 downto W0));
    return data;
  end function;
  constant t_output_slvcodecwidth: natural := (1+fixed_width);
  function to_slvcodec (constant data: t_output) return std_logic_vector;
  function from_slvcodec (constant slv: std_logic_vector) return t_output;
  function to_slvcodec (constant data: t_output) return std_logic_vector is
    constant W0: natural := 0;
    constant W1: natural := W0 + (1+fixed_width);
    variable slv: std_logic_vector(t_output_slvcodecwidth-1 downto 0);
  begin
    slv(W1-1 downto W0) := to_slvcodec(data.o);
    return slv;
  end function;

  function from_slvcodec (constant slv: std_logic_vector) return t_output is
    constant W0: natural := 0;
    constant W1: natural := W0 + (1+fixed_width);
    variable data: t_output;
    variable mapped: std_logic_vector(t_output_slvcodecwidth-1 downto 0);
  begin
    mapped := slv;
    data.o := from_slvcodec(mapped(W1-1 downto W0));
    return data;
  end function;
  signal input_data: t_input;
  signal output_data: t_output;
  signal input_slv: std_logic_vector(t_input_slvcodecwidth-1 downto 0);
  signal output_slv: std_logic_vector(t_output_slvcodecwidth-1 downto 0);
  signal clk: std_logic;
  signal read_clk: std_logic;
  signal write_clk: std_logic;
begin

  input_data <= from_slvcodec(input_slv);
  output_slv <= to_slvcodec(output_data);

  file_reader: entity work.ReadFile
    generic map(FILENAME => OUTPUT_PATH & "/indata.dat",
                PASSED_RUNNER_CFG => RUNNER_CFG,
                WIDTH => t_input_slvcodecwidth)
    port map(clk => read_clk,
             out_data => input_slv);

  file_writer: entity work.WriteFile
    generic map(FILENAME => OUTPUT_PATH & "/outdata.dat",
                WIDTH => t_output_slvcodecwidth)
    port map(clk => write_clk,
             in_data => output_slv);

  clock_generator: entity work.ClockGenerator
    generic map(CLOCK_PERIOD => CLOCK_PERIOD,
                CLOCK_OFFSET => 0 ns
                )
    port map(clk => clk);

  read_clock_generator: entity work.ClockGenerator
    generic map(CLOCK_PERIOD => CLOCK_PERIOD,
                CLOCK_OFFSET => CLOCK_PERIOD/10
                )
    port map(clk => read_clk);

  write_clock_generator: entity work.ClockGenerator
    generic map(CLOCK_PERIOD => CLOCK_PERIOD,
                CLOCK_OFFSET => 4*CLOCK_PERIOD/10
                )
    port map(clk => write_clk);

  dut: entity work.complex_mag2
    port map(
             i => input_data.i,
o => output_data.o
             );

end architecture;

But generating a test bench that just reads and writes the input and output data to and from files isn’t particularly useful unless we have a way of generating the input data, and checking the output data. Slvcodec include tools to do this with python.

Python-based testing

We define a python class with a make_input_data method that returns an iterable of dictionaries specifying the input data, and a check_output_data method that receives a list of input_data dictionaries and a list of output data dictionaries, that raises an exeception is the output data is incorrect.

class ComplexMag2Test:

    def __init__(self, resolved, generics, top_params):
        # Here we're taking advantage of the fact that when the test is intialized it
        # has access to the parsed VHDL.  We use that to get the value of the constant
        # FIXED_WIDTH that is defined in complex_pkg.vhd.
        self.fixed_width = resolved['packages']['complex'].constants['fixed_width'].value()
        self.max_fixed = pow(2, self.fixed_width-1)-1
        self.min_fixed = -pow(2, self.fixed_width-1)
        self.n_data = 100

    def fixed_to_float(self, f):
        r = f / pow(2, self.fixed_width-2)
        return r

    def make_input_data(self, seed=None, n_data=3000):
        input_data = [{
            'i': {'real': random.randint(self.min_fixed, self.max_fixed),
                  'imag': random.randint(self.min_fixed, self.max_fixed)},
        } for i in range(self.n_data)]

        return input_data

    def check_output_data(self, input_data, output_data):
        inputs = [self.fixed_to_float(d['i']['real']) + self.fixed_to_float(d['i']['imag']) * 1j
                  for d in input_data]
        input_float_mag2s = [abs(v)*abs(v) for v in inputs]
        outputs = [self.fixed_to_float(d['o']) for d in output_data]
        differences = [abs(expected - actual) for expected, actual in zip(input_float_mag2s, outputs)]
        allowed_error = 1/pow(2, self.fixed_width-2)
        assert all([d < allowed_error for d in differences])

We then use slvcodec.test_utils.register_test_with_vunit to generate an appropriate testbench and input data file, and register the produced test with vunit. VUnit can then be run as normal.

from slvcodec import test_utils, config
import os

if __name__ == '__main__':
    random.seed(0)
    # Initialize vunit with command line parameters.
    vu = config.setup_vunit()
    # Set up logging.
    config.setup_logging(vu.log_level)
    # Get filenames for test
    this_dir = os.path.dirname(os.path.realpath(__file__))
    filenames = [
        os.path.join(this_dir, 'complex_pkg.vhd'),
        os.path.join(this_dir, 'complex_mag2.vhd'),
        ]
    # Register the test with VUnit.
    test_output_directory = os.path.join(this_dir, 'generated')
    test_utils.register_test_with_vunit(
        vu=vu,
        directory=test_output_directory,
        filenames=filenames,
        top_entity='complex_mag2',
        all_generics=[{}],
        test_class=ComplexMag2Test,
        top_params={},
        )
    # Run the tests with VUnit
    vu.set_sim_option('disable_ieee_warnings', True)
    vu.main()