Float constants

Register constants can be of type float for decimal numeric values. This page will show you how the set up float constants, as well as showcase all the code that can be generated from it.

Usage in TOML

The TOML file below shows how to set up a register list with two float constants. Note that in the TOML, the type of the constant is determined by the type of the literal value.

TOML that sets up a register list with float constants.

# This will allocate a register constant with the name "clock_frequency_hz" of type float.
[constant.clock_frequency_hz]

# The "value" property MUST be present for a float constant.
# The value specified must be a float.
value = 156.25e6

# The "description" property is optional for a constant. Will default to "" if not specified.
# The value specified must be a string.
description = "The frequency in Hertz of the system clock."


[constant.division_factor]

value = 8.125

Note that the second constant does not have a description specified, meaning it will default to an empty string.

Below you will see how you can parse this TOML file and generate artifacts from it.

Usage with Python API

The Python code below shows

How to parse the TOML file listed above.
How to create an identical register list when instead using the Python API.
How to generate register artifacts.

Note that the result of the create_from_api call is identical to that of the parse_toml call. Meaning that using a TOML file or using the Python API is completely equivalent. You choose yourself which method you want to use in your code base.

Python code that sets up a register list with float constants.

# Standard libraries
import sys
from pathlib import Path

# First party libraries
from hdl_registers.generator.c.header import CHeaderGenerator
from hdl_registers.generator.cpp.interface import CppInterfaceGenerator
from hdl_registers.generator.html.page import HtmlPageGenerator
from hdl_registers.generator.vhdl.register_package import VhdlRegisterPackageGenerator
from hdl_registers.parser.toml import from_toml
from hdl_registers.register_list import RegisterList

THIS_DIR = Path(__file__).parent


def parse_toml() -> RegisterList:
    """
    Create the register list by parsing a TOML data file.
    """
    return from_toml(name="caesar", toml_file=THIS_DIR.parent / "toml" / "constant_float.toml")


def create_from_api() -> RegisterList:
    """
    Alternative method: Create the register list by using the Python API.
    """
    register_list = RegisterList(name="caesar")

    register_list.add_constant(
        name="clock_frequency_hz",
        value=156.25e6,
        description="The frequency in Hertz of the system clock.",
    )

    register_list.add_constant(
        name="division_factor",
        value=8.125,
        description="",
    )

    return register_list


def generate(register_list: RegisterList, output_folder: Path):
    """
    Generate the artifacts that we are interested in.
    """
    CHeaderGenerator(register_list=register_list, output_folder=output_folder).create()
    CppInterfaceGenerator(register_list=register_list, output_folder=output_folder).create()
    HtmlPageGenerator(register_list=register_list, output_folder=output_folder).create()
    VhdlRegisterPackageGenerator(register_list=register_list, output_folder=output_folder).create()


def main(output_folder: Path):
    generate(register_list=parse_toml(), output_folder=output_folder / "toml")
    generate(register_list=create_from_api(), output_folder=output_folder / "api")


if __name__ == "__main__":
    main(output_folder=Path(sys.argv[1]))

See RegisterList.add_constant() for more Python API details.

Generated code

See below for a description of the code that can be generated with these constants.

Note that the examples on this page set up a register list with only constants, no registers. This allowed of course, but albeit a little bit rare.

HTML page

See HTML file below for the human-readable documentation that is produced by the generate() call in the Python example above.

HTML page

VHDL package

The VHDL code below is produced by the generate() call in the Python example above. Click the button to expand and view the code.

Click to expand/collapse code.

Generated VHDL code.

-- This file is automatically generated by hdl-registers version 5.1.4-dev.
-- Code generator VhdlRegisterPackageGenerator version 1.0.0.
-- Generated 2024-04-26 20:51 at commit 2c446088490c1e41.
-- Register hash 0714452eca8344345f74c255d84afc12334b4cb9.

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.fixed_pkg.all;

library reg_file;
use reg_file.reg_file_pkg.all;


package caesar_regs_pkg is

  -- ---------------------------------------------------------------------------
  -- Values of register constants.
  constant caesar_constant_clock_frequency_hz : real := 156250000.0;
  constant caesar_constant_division_factor : real := 8.125;

end package;

C++ interface

The C++ interface header code below is produced by the generate() call in the Python example above. Click the button to expand and view the code.

Click to expand/collapse code.

Generated C++ interface class code.

// This file is automatically generated by hdl-registers version 5.1.4-dev.
// Code generator CppInterfaceGenerator version 1.0.0.
// Generated 2024-04-26 20:51 at commit 2c446088490c1e41.
// Register hash 0714452eca8344345f74c255d84afc12334b4cb9.

#pragma once

#include <cassert>
#include <cstdint>
#include <cstdlib>

namespace fpga_regs
{

  class ICaesar
  {
  public:
    // Register constant.
    static constexpr double clock_frequency_hz = 156250000.0;
    // Register constant.
    static constexpr double division_factor = 8.125;

    // Number of registers within this register map.
    static const size_t num_registers = 0uL;

    virtual ~ICaesar() {}

  };

} /* namespace fpga_regs */

C header

The C code below is produced by the generate() call in the Python example above.

Click to expand/collapse code.

Generated C code.

// This file is automatically generated by hdl-registers version 5.1.4-dev.
// Code generator CHeaderGenerator version 1.0.0.
// Generated 2024-04-26 20:51 at commit 2c446088490c1e41.
// Register hash 0714452eca8344345f74c255d84afc12334b4cb9.

#ifndef CAESAR_REGS_H
#define CAESAR_REGS_H

// Value of register constant 'clock_frequency_hz'.
#define CAESAR_CLOCK_FREQUENCY_HZ (156250000.0)
// Value of register constant 'division_factor'.
#define CAESAR_DIVISION_FACTOR (8.125)

// Number of registers within this register map.
#define CAESAR_NUM_REGS (0u)

// Type for this register map.
typedef struct caesar_regs_t
{
} caesar_regs_t;

#endif // CAESAR_REGS_H