Feetech.ControlTable behaviour (feetech v0.2.4)

Behaviour for servo-specific control table definitions.

Each servo model has a different memory layout (control table) that defines the addresses, sizes, and conversions for readable/writable parameters.

Implementing a Control Table

defmodule MyServo do
  @behaviour Feetech.ControlTable

  @impl true
  def model_name, do: "MyServo"

  @impl true
  def registers do
    %{
      id: {5, 1, nil},
      goal_position: {42, 2, :position},
      present_position: {56, 2, :position}
    }
  end
end

Conversion Types

The third element of each register tuple specifies how to convert between raw register values and user-friendly values:

nil - No conversion, raw integer value
:bool - 0/1 to false/true
float - Scale factor (e.g., 0.1 for voltage in 0.1V units)
:position - Steps to radians (unsigned, servo-specific)
:position_signed - Steps to radians with sign-magnitude encoding (bit 15 = sign)
:speed - Speed units to rad/s
:speed_signed - Signed speed to rad/s (sign-magnitude, bit 15 = sign)
:load_signed - Signed load percentage (sign-magnitude, bit 10 = sign)
:mode - Operating mode enum
:baud_rate - Baud rate enum
{:sign_magnitude, sign_bit} - Raw sign-magnitude with specified sign bit
{module, decode_fun, encode_fun} - Custom conversion functions

Summary

Types

address()

Memory address in control table

byte_length()

Number of bytes for register

conversion()

Conversion specification for translating between raw and user values.

register_def()

register_name()

registers()

Map of register names to their definitions

Callbacks

model_name()

Returns the human-readable model name

registers()

Returns the register definitions map

Functions

decode(control_table, name, data)

Decodes raw bytes from a register to a user value.

decode_raw(data)

Decodes raw bytes to an integer (no conversion).

encode(control_table, name, value)

Encodes a user value to raw bytes for writing to a register.

encode_raw(control_table, name, value)

Encodes a raw integer value to bytes (no conversion).

get_register(control_table, name)

Looks up a register definition by name.

Types

address()

@type address() :: non_neg_integer()

Memory address in control table

byte_length()

@type byte_length() :: 1 | 2 | 4

Number of bytes for register

conversion()

@type conversion() ::
  nil
  | :bool
  | :position
  | :position_signed
  | :speed
  | :speed_signed
  | :load_signed
  | :mode
  | :baud_rate
  | float()
  | {:sign_magnitude, non_neg_integer()}
  | {module(), atom(), atom()}

Conversion specification for translating between raw and user values.

register_def()

@type register_def() :: {address(), byte_length(), conversion()}

register_name()

@type register_name() :: atom()

registers()

@type registers() :: %{required(register_name()) => register_def()}

Map of register names to their definitions

Callbacks

model_name()

@callback model_name() :: String.t()

Returns the human-readable model name

registers()

@callback registers() :: registers()

Returns the register definitions map

Functions

decode(control_table, name, data)

@spec decode(module(), register_name(), binary()) :: {:ok, term()} | {:error, atom()}

Decodes raw bytes from a register to a user value.

decode_raw(data)

@spec decode_raw(binary()) :: integer()

Decodes raw bytes to an integer (no conversion).

encode(control_table, name, value)

@spec encode(module(), register_name(), term()) :: {:ok, binary()} | {:error, atom()}

Encodes a user value to raw bytes for writing to a register.

encode_raw(control_table, name, value)

@spec encode_raw(module(), register_name(), integer()) ::
  {:ok, binary()} | {:error, atom()}

Encodes a raw integer value to bytes (no conversion).

get_register(control_table, name)

@spec get_register(module(), register_name()) ::
  {:ok, register_def()} | {:error, :unknown_register}

Looks up a register definition by name.