Messages

Still Under Development

Why?

I find myself constantly changing message formats in one language and then another is out of sync. This way, if I change the message format, it is easy to recompile for both Python and C++. For the actual serialization I use yivo.

Why not use insert favorit here?

• protobuf: generates massive header files and I want this to run on small micro controllers
• msgpack: more serialization than defining messages

Why toml?

It seemed good enough and it is used for configuration. There is no reason I couldn't switch the front end from toml to json or something else. All I need is a python dictionary to be feed info create_c/py. I just wanted a parser to real some file and return a dictionary of information.

Architecture

---
title: Key Functions
---
flowchart LR
    A(read_toml file ) --> |dict| C(to list);
    B(read_tomls str ) --> |dict| C;
    C --> |list| E(process_messages)
    D(read_folder path) --> |list| E
    E --> |dict| F(create_cpp)
    E --> |dict| G(create_python)
    F --> |dict| H(write_file)
    G --> |dict| H
    I[(var_types)] --> |VarInfo|E

Loading

Message formats should be short and simple, but if you want, it can also be complex.

Binary

msgcomp [--out_dir=DIR][--in_dir=DIR][--version][--verbose][--help][--cpp-only][--python-only]

$ gmsg 
Found 9 message files
Namespace: quad
 MsgID NAME
------------------------
 -   1 vec
 -   2 quat
 -   3 twist
 -   4 wrench
 -   5 pose
 -  20 heartbeat
 -  40 calibration_t
 -  40 imu_raw_t
 -  41 imu_t
[ C++ ]
 Saving to /Users/kevin/github/quadcopter/messages/cpp
 -> vec_t.hpp
 -> quat_t.hpp
 -> twist_t.hpp
 -> wrench_t.hpp
 -> pose_t.hpp
 -> calibration_t.hpp
 -> imu_raw_t.hpp
 -> imu_t.hpp
 -> heartbeat.hpp
[ Python ]
 Saving to /Users/kevin/github/quadcopter/messages/python
 -> vec_t.py
 -> quat_t.py
 -> twist_t.py
 -> wrench_t.py
 -> pose_t.py
 -> calibration_t.py
 -> imu_raw_t.py
 -> imu_t.py
 -> heartbeat.py

Message File Data Types

Messages can use standard language types:

Message	C	Python
[u]int8	[u]int8_t	int
[u]int16	[u]int16_t	int
[u]int32	[u]int32_t	int
[u]int64	[u]int64_t	int
float	float	float
double	double	double

Or complex types that were inspired by ROS:

ID	Message	Info
1	vec	{float x,y,z}
2	quat	{float w,x,y,z}
3	twist	{vec_t linear, vec_t angular}
4	wrench	{vec_t force, vec_t torque}
5	pose	{vec_t position, quat_t orientation}

Global

Now you can shorten your message file because a lot of the keys are repetitive across message files. Basically, anything in the “global” space of a message file can be moved to a global.toml file instead of putting it into a message file.

[global]
comments = "string"
namespace = "string"
license = "string" # full text of what you want at the top of each file
version = "string" # anything you want like 1.0.2 or 2022.2.23
frozen = "bool"    # is python dataclass frozen true or false
wrap_width = "int" # line width for text wrapping, default = 70

[global.serialize]
yivo = "bool"         # true | false
mavlink = "bool"

# put native types in var_types VarTypes(name, size, fmt, id) ... native ids = 0,
# complex ids > 0, remove complex altogether ids between 20 - 255. This is nice
# to put message ids here, because you can see them all in one place and know you don’t
# have any conflicts.
[global.ids]
imu_t = "int"
calibration_t = "int"
my_cool_msg = "int"
awesome_msg = "int"

Message

[enum.name] # optional, can have many of these, each must have
            # an original name and each value in an enum must
            # be unique (python uses `@unique` from `enum`
            # library)
Val1 = 1
Val2 = 2
Val3 = 3

# since python is not a strongly typed language, it will not always respect
# default types, so what should be an array (float[3]), you can set to a
# scalar int. C is the only one that will complain if you do this.
[message]
# type-var_name = array_dimension
x = "float"                    # float x = 0 or default
y = {type = "float", len = 2}  # float y[2]{0,0} or default
z = "float"                    # var names can only be ascii letters, numbers and -
a = {type = "vec", len = 2, default = [[0,0,0],[0,0,0]]}  # vec_t a[2]{{0,0,0},{0,0,0}}
                                                          # add `#include “vec_t.hpp”` and
                                                          # `from vec_t import *` when generated

comments = "string" # optional, will be attached to the `struct`
id = "bool"         # can be in global.toml [ids] or here, value must be between 20 - 255
frozen = "bool"     # only for python dataclass

# this is really a message library for serialization, so only put functions if
# you really need to, otherwise, let some other part of your code base
# handle this
[functions]
c = "string"
python = "string"

The minimum message file is:

[message]
x = "float"
id = 33  # this can be in global.toml under [global.ids]
name = "simple"

Example

[message]
# var_name = type
# var_name = {type, len, default} only type is required
x = "uint32" # len = 1
y = {type = "float", len = 3, default = [0,0,0]}
z = {type = "uint8", default = 2} # len = 1
m = {type = "int16", len = 2}
name = "test"
id = 33

{'message': {'x': 'uint32', 'y': {'type': 'float', 'len': 3, 'default': [0, 0, 0]}, 'z': {'type': 'uint8', 'default': 2}, 'm': {'type': 'int16', 'len': 2}, 'name': 'test', 'id': 33}}

To Do

• Maybe move id and name to a meta key so you can have a key in the message that is call one of those two?

  [message]
  x = "float"
  [message.meta]
  id = 33  # this can be in global.toml under [global.ids]
  name = "simple"

• Maybe include [message.method] {c = "string", py = "string"}
• Maybe do x = "int" or x = {type = 'int', len = 3, default = [0,0,0]}?
• Fix python 3.8 - 3.10 with tomlkit
  • tomlkit doesn't seem to work ... just stick with tomllib?
• Fix comments ... do I need them?
• Add global wrap size default to 70 char wide
• Add py and c for builtin messages, want vec in message and vec_t in c
• Fix or remove automatic defaults, messages with new types are not getting setup correctly with defaults. Only allow custom defaults for new messages? Maybe embed default in each type class or None if no default? Still don't like how I am doing defaults or if they are needed
  • Add defaults to variable
  • OR add one default for whole message
  • If default available use it
  • If custom default in message available, it has priority

Potential new tpes:

Message	C	Python
dynamic array	vector	list

ros 2 types

MIT License

Copyright (c) 2023 gecko-robotics

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