Enumeration fields

Register fields can be of the type enumeration. Meaning, a field that can only take on a limited, pre-defined, and named, set of values. This is a very common and highly useful programming concept. See Wikipedia if you are unfamiliar with this: https://en.wikipedia.org/wiki/Enumerated_type

This page will show you how the set up enumeration fields in a register, and will showcase all the code that can be generated from it.

Usage in TOML

The TOML file below shows how to set up a register with two enumeration fields. See comments for rules about the different properties.

TOML that sets up a register with enumeration fields.

[conf]

mode = "r_w"
description = "Configuration register."

# This will allocate an enumeration field named "severity_level" in the "conf" register.
# The "type" property MUST be present and set to "enumeration".
severity_level.type = "enumeration"

# The "description" property is OPTIONAL for an enumeration field.
# Will default to "" if not specified.
# The value specified MUST be a string.
severity_level.description = "Run-time configuration of severity."

# The "default_value" property is OPTIONAL for an enumeration field.
# Will default to the first enumeration element declared below, if not specified.
# The value specified MUST be a string that matches one of the enumeration element names
# specified below.
severity_level.default_value = "warning"

# For an enumeration field there MUST be at least one enumeration element declared.
# The name of each element is mapped below to the description of that element.
severity_level.element.info = "Informational message. Is not considered an error."
severity_level.element.warning = "Warning message. Is not considered an error."
severity_level.element.error = "Error message. Is considered an error."
severity_level.element.failure = "Failure message. Is considered an error."


packet_source.type = "enumeration"
packet_source.description = "Set input mux."
packet_source.element.streaming = "Process incoming streaming data."
packet_source.element.dma = "Read packets from DMA."
packet_source.element.disabled = "Don't send anything."

Note that the second field does not have any default value, meaning that it will automatically default to the first element (streaming).

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

1. How to parse the TOML file listed above.

2. How to create an identical register list when instead using the Python API.

3. 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 with enumeration fields.

import sys
from pathlib import Path

from hdl_registers.generator.c.header import CHeaderGenerator
from hdl_registers.generator.cpp.implementation import CppImplementationGenerator
from hdl_registers.generator.cpp.interface import CppInterfaceGenerator
from hdl_registers.generator.html.page import HtmlPageGenerator
from hdl_registers.generator.vhdl.record_package import VhdlRecordPackageGenerator
from hdl_registers.generator.vhdl.register_package import VhdlRegisterPackageGenerator
from hdl_registers.parser.toml import from_toml
from hdl_registers.register_list import RegisterList
from hdl_registers.register_modes import REGISTER_MODES

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" / "field_enumeration.toml")


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

    register = register_list.append_register(
        name="conf", mode=REGISTER_MODES["r_w"], description="Configuration register."
    )

    register.append_enumeration(
        name="severity_level",
        description="Run-time configuration of severity.",
        elements={
            "info": "Informational message. Is not considered an error.",
            "warning": "Warning message. Is not considered an error.",
            "error": "Error message. Is considered an error.",
            "failure": "Failure message. Is considered an error.",
        },
        default_value="warning",
    )

    register.append_enumeration(
        name="packet_source",
        description="Set input mux.",
        elements={
            "streaming": "Process incoming streaming data.",
            "dma": "Read packets from DMA.",
            "disabled": "Don't send anything.",
        },
        default_value="streaming",
    )

    return register_list


def generate(register_list: RegisterList, output_folder: Path) -> None:
    """
    Generate the artifacts that we are interested in.
    """
    CHeaderGenerator(register_list=register_list, output_folder=output_folder).create()

    CppImplementationGenerator(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()
    VhdlRecordPackageGenerator(register_list=register_list, output_folder=output_folder).create()


def main(output_folder: Path) -> None:
    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 Register.append_enumeration() and the Enumeration class for more Python API details.

Generated code

See below for a description of the code that can be generated when using enumeration fields.

HTML page

See HTML file below for the human-readable documentation that is produced by the generate() call in the Python example above. Each enumeration field is documented and the description of each element is included.

See HTML generator for more details about the HTML generator and its capabilities.

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. See VHDL generator for instructions on how it can be used in your VHDL project.

Base register package

Some interesting things to notice:

1. There is only one register, at index 0.

2. The first field is two bits wide, occupying bits 1 and 0, while the second one is only one bit wide, occupying but 3.

3. VHDL supports enumeration types natively. The elements of the enumeration are exposed to the scope of the package, and all files that include it.

4. For each enumeration field, there are conversion functions for

   1. Converting from the enumeration type to std_logic_vector.

   2. Slicing a register value at the correct range and converting from std_logic_vector to enumeration.

Click to expand/collapse code.

Generated VHDL register package.

-- -----------------------------------------------------------------------------
-- This file is automatically generated by hdl-registers version 8.0.2-dev.
-- Code generator VhdlRegisterPackageGenerator version 2.0.0.
-- Generated 2025-05-31 20:51 at Git commit 76c4bba75025.
-- Register hash cddf2158e621e8c886df3b685f3035d60205acc1.
-- -----------------------------------------------------------------------------

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

library register_file;
use register_file.register_file_pkg.all;


package caesar_regs_pkg is

  -- ---------------------------------------------------------------------------
  -- The valid range of register indexes.
  subtype caesar_register_range is natural range 0 to 0;

  -- ---------------------------------------------------------------------------
  -- The number of bits needed to address all 1 registers on a register bus.
  -- Note that this figure includes the lowest two address bits that are assumed zero, since
  -- registers are 32-bit and unaligned accesses are not supported.
  constant caesar_address_width : positive := 3;

  -- Register indexes, within the list of registers.
  constant caesar_conf : natural := 0;

  -- Declare 'register_map' and 'regs_init' constants here but define them in
  -- the package body (deferred constants).
  -- So that functions have been elaborated when they are called.
  -- Needed for ModelSim compilation to pass.

  -- To be used as the 'registers' generic of 'axi_lite_register_file.vhd'.
  constant caesar_register_map : register_definition_vec_t(caesar_register_range);

  -- To be used for the 'regs_up' and 'regs_down' ports of 'axi_lite_register_file.vhd'.
  subtype caesar_regs_t is register_vec_t(caesar_register_range);
  -- To be used as the 'default_values' generic of 'axi_lite_register_file.vhd'.
  constant caesar_regs_init : caesar_regs_t;

  -- To be used for the 'reg_was_read' and 'reg_was_written' ports of 'axi_lite_register_file.vhd'.
  subtype caesar_reg_was_accessed_t is std_ulogic_vector(caesar_register_range);

  -- -----------------------------------------------------------------------------
  -- Fields in the 'conf' register.
  -- Range of the 'severity_level' field.
  subtype caesar_conf_severity_level is natural range 1 downto 0;
  -- Width of the 'severity_level' field.
  constant caesar_conf_severity_level_width : positive := 2;
  -- Type for the 'severity_level' field.
  type caesar_conf_severity_level_t is (
    severity_level_info,
    severity_level_warning,
    severity_level_error,
    severity_level_failure
  );
  -- Default value of the 'severity_level' field.
  constant caesar_conf_severity_level_init : caesar_conf_severity_level_t := severity_level_warning;
  -- Type for the 'severity_level' field as an SLV.
  subtype caesar_conf_severity_level_slv_t is std_ulogic_vector(1 downto 0);
  -- Cast a 'severity_level' field value to SLV.
  function to_slv(data : caesar_conf_severity_level_t) return caesar_conf_severity_level_slv_t;
  -- Get a 'severity_level' field value from a register value.
  function to_caesar_conf_severity_level(data : register_t) return caesar_conf_severity_level_t;

  -- Range of the 'packet_source' field.
  subtype caesar_conf_packet_source is natural range 3 downto 2;
  -- Width of the 'packet_source' field.
  constant caesar_conf_packet_source_width : positive := 2;
  -- Type for the 'packet_source' field.
  type caesar_conf_packet_source_t is (
    packet_source_streaming,
    packet_source_dma,
    packet_source_disabled
  );
  -- Default value of the 'packet_source' field.
  constant caesar_conf_packet_source_init : caesar_conf_packet_source_t := packet_source_streaming;
  -- Type for the 'packet_source' field as an SLV.
  subtype caesar_conf_packet_source_slv_t is std_ulogic_vector(1 downto 0);
  -- Cast a 'packet_source' field value to SLV.
  function to_slv(data : caesar_conf_packet_source_t) return caesar_conf_packet_source_slv_t;
  -- Get a 'packet_source' field value from a register value.
  function to_caesar_conf_packet_source(data : register_t) return caesar_conf_packet_source_t;

end package;

package body caesar_regs_pkg is

  constant caesar_register_map : register_definition_vec_t(caesar_register_range) := (
    0 => (index => caesar_conf, mode => r_w, utilized_width => 4)
  );

  constant caesar_regs_init : caesar_regs_t := (
    0 => "00000000000000000000000000000001"
  );

  -- Cast a 'severity_level' field value to SLV.
  function to_slv(data : caesar_conf_severity_level_t) return caesar_conf_severity_level_slv_t is
    constant data_int : natural := caesar_conf_severity_level_t'pos(data);
    constant result : caesar_conf_severity_level_slv_t := std_ulogic_vector(
      to_unsigned(data_int, caesar_conf_severity_level_width)
    );
  begin
    return result;
  end function;

  -- Get a 'severity_level' field value from a register value.
  function to_caesar_conf_severity_level(data : register_t) return caesar_conf_severity_level_t is
    constant field_slv : caesar_conf_severity_level_slv_t := data(caesar_conf_severity_level);
    constant field_int : natural := to_integer(unsigned(field_slv));
    constant result : caesar_conf_severity_level_t := caesar_conf_severity_level_t'val(field_int);
  begin
    return result;
  end function;

  -- Cast a 'packet_source' field value to SLV.
  function to_slv(data : caesar_conf_packet_source_t) return caesar_conf_packet_source_slv_t is
    constant data_int : natural := caesar_conf_packet_source_t'pos(data);
    constant result : caesar_conf_packet_source_slv_t := std_ulogic_vector(
      to_unsigned(data_int, caesar_conf_packet_source_width)
    );
  begin
    return result;
  end function;

  -- Get a 'packet_source' field value from a register value.
  function to_caesar_conf_packet_source(data : register_t) return caesar_conf_packet_source_t is
    constant field_slv : caesar_conf_packet_source_slv_t := data(caesar_conf_packet_source);
    constant field_int : natural := to_integer(unsigned(field_slv));
    constant result : caesar_conf_packet_source_t := caesar_conf_packet_source_t'val(field_int);
  begin
    return result;
  end function;

end package body;

Record package

The caesar_regs_down_t type is a record with a member config, the only register in this example. The type of the config member is another record with the two enumerations set up in our example: severity_level and packet_source. These are of enumeration types defined in the base register package above.

In our VHDL code we can access a field value for example like this:

if regs_down.config.packet_source = packet_source_streaming then
  result_valid <= input_valid;
elsif regs_down.config.packet_source = packet_source_dma then
  result_valid <= job_valid;
else
  -- packet_source_disabled
  result_valid <= '0';
end if;

Click to expand/collapse code.

Generated VHDL record package.

-- -----------------------------------------------------------------------------
-- This file is automatically generated by hdl-registers version 8.0.2-dev.
-- Code generator VhdlRecordPackageGenerator version 1.0.0.
-- Generated 2025-05-31 20:51 at Git commit 76c4bba75025.
-- Register hash cddf2158e621e8c886df3b685f3035d60205acc1.
-- -----------------------------------------------------------------------------

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

library register_file;
use register_file.register_file_pkg.register_t;

use work.caesar_regs_pkg.all;


package caesar_register_record_pkg is

  -- -----------------------------------------------------------------------------
  -- Record with correctly-typed members for each field in each register.
  -- Fields in the 'conf' register as a record.
  type caesar_conf_t is record
    severity_level : caesar_conf_severity_level_t;
    packet_source : caesar_conf_packet_source_t;
  end record;
  -- Default value for the 'conf' register as a record.
  constant caesar_conf_init : caesar_conf_t := (
    severity_level => caesar_conf_severity_level_init,
    packet_source => caesar_conf_packet_source_init
  );
  -- Convert a record of the 'conf' register to SLV.
  function to_slv(data : caesar_conf_t) return register_t;
  -- Convert an SLV register value to the record for the 'conf' register.
  function to_caesar_conf(data : register_t) return caesar_conf_t;

  -- -----------------------------------------------------------------------------
  -- Below is a record with correctly typed and ranged members for all registers, register arrays
  -- and fields that are in the 'down' direction.
  -- Record with everything in the 'down' direction.
  type caesar_regs_down_t is record
    conf : caesar_conf_t;
  end record;
  -- Default value of the above record.
  constant caesar_regs_down_init : caesar_regs_down_t := (
    conf => caesar_conf_init
  );
  -- Convert SLV register list to record with everything in the 'down' direction.
  function to_caesar_regs_down(data : caesar_regs_t) return caesar_regs_down_t;

  -- ---------------------------------------------------------------------------
  -- Below is a record with a status bit for each readable register in the register list.
  -- It can be used for the 'reg_was_read' port of a register file wrapper.
  -- Combined status mask record for all readable register.
  type caesar_reg_was_read_t is record
    conf : std_ulogic;
  end record;
  -- Default value for the above record.
  constant caesar_reg_was_read_init : caesar_reg_was_read_t := (
    others => '0'
  );
  -- Convert an SLV 'reg_was_read' from generic register file to the record above.
  function to_caesar_reg_was_read(
    data : caesar_reg_was_accessed_t
  ) return caesar_reg_was_read_t;

  -- ---------------------------------------------------------------------------
  -- Below is a record with a status bit for each writeable register in the register list.
  -- It can be used for the 'reg_was_written' port of a register file wrapper.
  -- Combined status mask record for all writeable register.
  type caesar_reg_was_written_t is record
    conf : std_ulogic;
  end record;
  -- Default value for the above record.
  constant caesar_reg_was_written_init : caesar_reg_was_written_t := (
    others => '0'
  );
  -- Convert an SLV 'reg_was_written' from generic register file to the record above.
  function to_caesar_reg_was_written(
    data : caesar_reg_was_accessed_t
  ) return caesar_reg_was_written_t;

end package;

package body caesar_register_record_pkg is

  function to_slv(data : caesar_conf_t) return register_t is
    variable result : register_t := (others => '-');
  begin
    result(caesar_conf_severity_level) := to_slv(data.severity_level);
    result(caesar_conf_packet_source) := to_slv(data.packet_source);

    return result;
  end function;

  function to_caesar_conf(data : register_t) return caesar_conf_t is
    variable result : caesar_conf_t := caesar_conf_init;
  begin
    result.severity_level := to_caesar_conf_severity_level(data);
    result.packet_source := to_caesar_conf_packet_source(data);

    return result;
  end function;

  function to_caesar_regs_down(data : caesar_regs_t) return caesar_regs_down_t is
    variable result : caesar_regs_down_t := caesar_regs_down_init;
  begin
    result.conf := to_caesar_conf(data(caesar_conf));

    return result;
  end function;

  function to_caesar_reg_was_read(
    data : caesar_reg_was_accessed_t
  ) return caesar_reg_was_read_t is
    variable result : caesar_reg_was_read_t := caesar_reg_was_read_init;
  begin
    result.conf := data(caesar_conf);

    return result;
  end function;

  function to_caesar_reg_was_written(
    data : caesar_reg_was_accessed_t
  ) return caesar_reg_was_written_t is
    variable result : caesar_reg_was_written_t := caesar_reg_was_written_init;
  begin
    result.conf := data(caesar_conf);

    return result;
  end function;

end package body;

C++

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

The class header is skipped here, since its inclusion would make this page very long. See C++ generator for more details and an example of how the excluded file might look.

C++ interface header

Some interesting things to notice in the interface header:

1. The valid enumeration values are defined using a C++ enum declaration in the namespace of each field.

2. The setters and getters for each field value use the enumeration type as argument or return value.

Click to expand/collapse code.

Generated C++ interface class code.

// -----------------------------------------------------------------------------
// This file is automatically generated by hdl-registers version 8.0.2-dev.
// Code generator CppInterfaceGenerator version 1.0.0.
// Generated 2025-05-31 20:51 at Git commit 76c4bba75025.
// Register hash cddf2158e621e8c886df3b685f3035d60205acc1.
// -----------------------------------------------------------------------------

#pragma once

#include <sstream>
#include <cstdint>
#include <cstdlib>

namespace fpga_regs
{

  namespace caesar
  {

    // Attributes for the 'conf' register.
    namespace conf {
      // Attributes for the 'severity_level' field.
      namespace severity_level
      {
        // The number of bits that the field occupies.
        static const size_t width = 2;
        // The bit index of the lowest bit in the field.
        static const size_t shift = 0;
        // The bit mask of the field, at index zero.
        static const uint32_t mask_at_base = (1uLL << width) - 1;
        // The bit mask of the field, at the field's bit index.
        static const uint32_t mask_shifted = mask_at_base << shift;

        // The valid elements for this enumeration field.
        enum Enumeration
        {
          info = 0,
          warning = 1,
          error = 2,
          failure = 3,
        };

        // Initial value of the field at device startup/reset.
        static const Enumeration default_value = Enumeration::warning;
        // Raw representation of the initial value, at the the field's bit index.
        static const uint32_t default_value_raw = 1uL << shift;
      }

      // Attributes for the 'packet_source' field.
      namespace packet_source
      {
        // The number of bits that the field occupies.
        static const size_t width = 2;
        // The bit index of the lowest bit in the field.
        static const size_t shift = 2;
        // The bit mask of the field, at index zero.
        static const uint32_t mask_at_base = (1uLL << width) - 1;
        // The bit mask of the field, at the field's bit index.
        static const uint32_t mask_shifted = mask_at_base << shift;

        // The valid elements for this enumeration field.
        enum Enumeration
        {
          streaming = 0,
          dma = 1,
          disabled = 2,
        };

        // Initial value of the field at device startup/reset.
        static const Enumeration default_value = Enumeration::streaming;
        // Raw representation of the initial value, at the the field's bit index.
        static const uint32_t default_value_raw = 0uL << shift;
      }

      // Struct that holds the value of each field in the register,
      // in a native C++ representation.
      struct Value {
        severity_level::Enumeration severity_level;
        packet_source::Enumeration packet_source;
      };
      // Initial value of the register at device startup/reset.
      const Value default_value = {
        severity_level::default_value,
        packet_source::default_value,
      };
    }

  } // namespace caesar

  class ICaesar
  {
  public:
    // Number of registers within this register list.
    static const size_t num_registers = 1uL;

    virtual ~ICaesar() {}

    // -------------------------------------------------------------------------
    // Methods for the 'conf' register.
    // Mode 'Read, Write'.
    // -------------------------------------------------------------------------
    // Read the whole register value over the register bus.
    virtual caesar::conf::Value get_conf() const = 0;

    // Read the whole register value over the register bus.
    // This method returns the raw register value without any type conversion.
    virtual uint32_t get_conf_raw() const = 0;

    // Read the register and slice out the 'severity_level' field value.
    virtual caesar::conf::severity_level::Enumeration get_conf_severity_level() const = 0;

    // Read the register and slice out the 'packet_source' field value.
    virtual caesar::conf::packet_source::Enumeration get_conf_packet_source() const = 0;

    // Write the whole register value over the register bus.
    virtual void set_conf(
      caesar::conf::Value register_value
    ) const = 0;

    // Write the whole register value over the register bus.
    // This method takes a raw register value and does not perform any type conversion.
    virtual void set_conf_raw(
      uint32_t register_value
    ) const = 0;

    // Write the 'severity_level' field value.
    // Will read-modify-write the register.
    virtual void set_conf_severity_level(
      caesar::conf::severity_level::Enumeration field_value
    ) const = 0;

    // Write the 'packet_source' field value.
    // Will read-modify-write the register.
    virtual void set_conf_packet_source(
      caesar::conf::packet_source::Enumeration field_value
    ) const = 0;
    // -------------------------------------------------------------------------
  };

} // namespace fpga_regs

C++ implementation

Note that each getter casts a uint32_t value read from the register bus to the enumeration type.

Click to expand/collapse code.

Generated C++ class implementation code.

// -----------------------------------------------------------------------------
// This file is automatically generated by hdl-registers version 8.0.2-dev.
// Code generator CppImplementationGenerator version 2.0.2.
// Generated 2025-05-31 20:51 at Git commit 76c4bba75025.
// Register hash cddf2158e621e8c886df3b685f3035d60205acc1.
// -----------------------------------------------------------------------------

#include "include/caesar.h"

namespace fpga_regs
{

// Macros called by the register code below to check for runtime errors.
#ifdef NO_REGISTER_SETTER_ASSERT
  #define _SETTER_ASSERT_TRUE(expression, message) ((void)0)
#else
  #define _SETTER_ASSERT_TRUE(expression, message) (_ASSERT_TRUE(expression, message))
#endif

#ifdef NO_REGISTER_GETTER_ASSERT
  #define _GETTER_ASSERT_TRUE(expression, message) ((void)0)
#else
  #define _GETTER_ASSERT_TRUE(expression, message) (_ASSERT_TRUE(expression, message))
#endif

#ifdef NO_REGISTER_ARRAY_INDEX_ASSERT
  #define _ARRAY_INDEX_ASSERT_TRUE(expression, message) ((void)0)
#else
  #define _ARRAY_INDEX_ASSERT_TRUE(expression, message) (_ASSERT_TRUE(expression, message))
#endif

// Base macro called by the other macros.
#define _ASSERT_TRUE(expression, message)                                                      \
  {                                                                                            \
    if (!static_cast<bool>(expression)) {                                                      \
      std::ostringstream diagnostics;                                                          \
      diagnostics << "caesar.cpp:" << __LINE__ << ": " << message << ".";                      \
      std::string diagnostic_message = diagnostics.str();                                      \
      m_assertion_handler(&diagnostic_message);                                                \
    }                                                                                          \
  }

  Caesar::Caesar(uintptr_t base_address, bool (*assertion_handler) (const std::string*))
      : m_registers(reinterpret_cast<volatile uint32_t *>(base_address)),
        m_assertion_handler(assertion_handler)
  {
    // Empty
  }

  // ---------------------------------------------------------------------------
  // Methods for the 'conf' register.
  // Mode 'Read, Write'.
  // ---------------------------------------------------------------------------
  // Read the whole register value over the register bus.
  caesar::conf::Value Caesar::get_conf() const
  {
    const uint32_t raw_value = get_conf_raw();

    const caesar::conf::severity_level::Enumeration severity_level_value = get_conf_severity_level_from_raw(raw_value);
    const caesar::conf::packet_source::Enumeration packet_source_value = get_conf_packet_source_from_raw(raw_value);

    return {severity_level_value, packet_source_value};
  }

  // Read the whole register value over the register bus.
  // This method returns the raw register value without any type conversion.
  uint32_t Caesar::get_conf_raw() const
  {
    const size_t index = 0;
    const uint32_t raw_value = m_registers[index];

    return raw_value;
  }

  // Read the register and slice out the 'severity_level' field value.
  caesar::conf::severity_level::Enumeration Caesar::get_conf_severity_level() const
  {
    const uint32_t raw_value = get_conf_raw();

    return get_conf_severity_level_from_raw(raw_value);
  }

  // Slice out the 'severity_level' field value from a given raw register value.
  // Performs no operation on the register bus.
  caesar::conf::severity_level::Enumeration Caesar::get_conf_severity_level_from_raw(
    uint32_t register_value
  ) const
  {
    const uint32_t result_masked = register_value & caesar::conf::severity_level::mask_shifted;
    const uint32_t result_shifted = result_masked >> caesar::conf::severity_level::shift;

    // "Cast" to the enum type.
    const auto field_value = caesar::conf::severity_level::Enumeration(result_shifted);

    return field_value;
  }

  // Read the register and slice out the 'packet_source' field value.
  caesar::conf::packet_source::Enumeration Caesar::get_conf_packet_source() const
  {
    const uint32_t raw_value = get_conf_raw();

    return get_conf_packet_source_from_raw(raw_value);
  }

  // Slice out the 'packet_source' field value from a given raw register value.
  // Performs no operation on the register bus.
  caesar::conf::packet_source::Enumeration Caesar::get_conf_packet_source_from_raw(
    uint32_t register_value
  ) const
  {
    const uint32_t result_masked = register_value & caesar::conf::packet_source::mask_shifted;
    const uint32_t result_shifted = result_masked >> caesar::conf::packet_source::shift;

    // "Cast" to the enum type.
    const auto field_value = caesar::conf::packet_source::Enumeration(result_shifted);

    _GETTER_ASSERT_TRUE(
      field_value <= 2,
      "Got 'packet_source' value out of range: " << field_value
    );

    return field_value;
  }

  // Write the whole register value over the register bus.
  void Caesar::set_conf(
    caesar::conf::Value register_value
  ) const
  {
    const uint32_t severity_level_value = get_conf_severity_level_to_raw(register_value.severity_level);
    const uint32_t packet_source_value = get_conf_packet_source_to_raw(register_value.packet_source);
    const uint32_t raw_value = severity_level_value | packet_source_value;

    set_conf_raw(raw_value);
  }

  // Write the whole register value over the register bus.
  // This method takes a raw register value and does not perform any type conversion.
  void Caesar::set_conf_raw(
    uint32_t register_value
  ) const
  {
    const size_t index = 0;
    m_registers[index] = register_value;
  }

  // Write the 'severity_level' field value.
  // Will read-modify-write the register.
  void Caesar::set_conf_severity_level(
    caesar::conf::severity_level::Enumeration field_value
  ) const
  {
    const size_t index = 0;

    const uint32_t raw_value = m_registers[index];
    const uint32_t mask_shifted_inverse = ~caesar::conf::severity_level::mask_shifted;
    const uint32_t base_value = raw_value & mask_shifted_inverse;

    const uint32_t field_value_raw = get_conf_severity_level_to_raw(field_value);
    const uint32_t register_value = base_value | field_value_raw;

    m_registers[index] = register_value;
  }

  // Get the raw representation of a given 'severity_level' field value.
  // Performs no operation on the register bus.
  uint32_t Caesar::get_conf_severity_level_to_raw(caesar::conf::severity_level::Enumeration field_value) const
  {
    _SETTER_ASSERT_TRUE(
      field_value <= 3,
      "Got 'severity_level' value out of range: " << field_value
    );

    const uint32_t field_value_casted = static_cast<uint32_t>(field_value);
    const uint32_t field_value_shifted = field_value_casted << caesar::conf::severity_level::shift;

    return field_value_shifted;
  }

  // Write the 'packet_source' field value.
  // Will read-modify-write the register.
  void Caesar::set_conf_packet_source(
    caesar::conf::packet_source::Enumeration field_value
  ) const
  {
    const size_t index = 0;

    const uint32_t raw_value = m_registers[index];
    const uint32_t mask_shifted_inverse = ~caesar::conf::packet_source::mask_shifted;
    const uint32_t base_value = raw_value & mask_shifted_inverse;

    const uint32_t field_value_raw = get_conf_packet_source_to_raw(field_value);
    const uint32_t register_value = base_value | field_value_raw;

    m_registers[index] = register_value;
  }

  // Get the raw representation of a given 'packet_source' field value.
  // Performs no operation on the register bus.
  uint32_t Caesar::get_conf_packet_source_to_raw(caesar::conf::packet_source::Enumeration field_value) const
  {
    _SETTER_ASSERT_TRUE(
      field_value <= 2,
      "Got 'packet_source' value out of range: " << field_value
    );

    const uint32_t field_value_casted = static_cast<uint32_t>(field_value);
    const uint32_t field_value_shifted = field_value_casted << caesar::conf::packet_source::shift;

    return field_value_shifted;
  }
  // ---------------------------------------------------------------------------

} // namespace fpga_regs

C header

The C code below is produced by the generate() call in the Python example above. The range and mask of the each field are available as constants. Note how the valid enumeration values are defined using a C enum declaration.

Click to expand/collapse code.

Generated C code.

// -----------------------------------------------------------------------------
// This file is automatically generated by hdl-registers version 8.0.2-dev.
// Code generator CHeaderGenerator version 1.0.0.
// Generated 2025-05-31 20:51 at Git commit 76c4bba75025.
// Register hash cddf2158e621e8c886df3b685f3035d60205acc1.
// -----------------------------------------------------------------------------

#ifndef CAESAR_REGS_H
#define CAESAR_REGS_H


// Number of registers within this register list.
#define CAESAR_NUM_REGS (1u)

// Type for this register list.
typedef struct caesar_regs_t
{
  // Mode "Read, Write".
  uint32_t conf;
} caesar_regs_t;

// Address of the 'conf' register.
// Mode 'Read, Write'.
#define CAESAR_CONF_INDEX (0u)
#define CAESAR_CONF_ADDR (4u * CAESAR_CONF_INDEX)
// Attributes for the 'severity_level' field in the 'conf' register.
#define CAESAR_CONF_SEVERITY_LEVEL_SHIFT (0u)
#define CAESAR_CONF_SEVERITY_LEVEL_MASK (0b11u << 0u)
#define CAESAR_CONF_SEVERITY_LEVEL_MASK_INVERSE (~CAESAR_CONF_SEVERITY_LEVEL_MASK)
enum CaesarConfSeverityLevel
{
  CAESAR_CONF_SEVERITY_LEVEL_INFO = 0,
  CAESAR_CONF_SEVERITY_LEVEL_WARNING = 1,
  CAESAR_CONF_SEVERITY_LEVEL_ERROR = 2,
  CAESAR_CONF_SEVERITY_LEVEL_FAILURE = 3,
};
// Attributes for the 'packet_source' field in the 'conf' register.
#define CAESAR_CONF_PACKET_SOURCE_SHIFT (2u)
#define CAESAR_CONF_PACKET_SOURCE_MASK (0b11u << 2u)
#define CAESAR_CONF_PACKET_SOURCE_MASK_INVERSE (~CAESAR_CONF_PACKET_SOURCE_MASK)
enum CaesarConfPacketSource
{
  CAESAR_CONF_PACKET_SOURCE_STREAMING = 0,
  CAESAR_CONF_PACKET_SOURCE_DMA = 1,
  CAESAR_CONF_PACKET_SOURCE_DISABLED = 2,
};

#endif // CAESAR_REGS_H