JETTY: Jarvis Serial to ROS-2 Transport Layer

My ROS based DIY robot( presented in the previous post) uses the NVIDIA Jetson Nano for high level robotic algorithms with the ROS 2 middle-ware. The Jetson is connected to an Arduino via a serial link for low-level hardware interaction and control.

As the Arduino is used for low-level communication with actuators/sensors. We need a software transport layer on top of the physical serial link (Jetson - Arduino) to stream (sensor) data/command from Arduino to ROS 2 and vice versa. On Dolly (my previous robot version), which used ROS 1, this was handled by Rosserial, a protocol for wrapping standard ROS serialized messages and multiplexing multiple topics and services over a serial link. On ROS 2, however, Rosserial is not available. Other alternative solutions exist but are not mature enough, some implementations require more computational resource which exceeds the capability of the Arduino Mega 2560.

So i decided to implement a dedicated transport layer for Jarvis called JETTY (Jarvis SErial to ROS-2 TransporT LaYer). I do not aim at a generic protocol for ROS to serial communication like ROS serial. Instead, the implementation of the transport layer should be specific only to the robot. However, the protocol must be easy to extend to adapt to any future upgrade of the robot such as adding more sensor/actuators.

Requirements on the transport layer:

  1. The transport layer must allow to stream data in form of frames (fixed size or not)
  2. Simple but reliable, unambiguous packet framing protocol, frame should be easy to identify
  3. Fast frame synchronization: When an endpoint (Arduino or ROS) connects to the Serial link in the middle of the data streaming, frame synchronization should be fast while minimizing the frames lost in the synchronization phase
  4. Frame should be verified using checksum before being consumed by an endpoint
  5. Packet framing overhead is allowed but need to be minimized
  6. The algorithms should be easy to implement and computationally inexpensive on both Jetson and Arduino

Brief, we need an efficient and reliable delimiting/synchronization scheme to detect the frame with short recovery time.

The detail on the choice of protocol and algorithm as well as insight implementation is presented on a section of my Jarvis booklet accessible via the following link:

https://doc.iohub.dev/jarvis/Ym9vazovLy9jXzIvc18xL0lOVFJPLm1k/JETTY:_Jarvis_Serial_to_ROS-2_transport_layer.md

Related posts

Comments

The comment editor supports Markdown syntax. Your email is necessary to notify you of further updates on the discussion. It will be hidden from the public.
Powered by antd server, (c) 2017 - 2021 Xuan Sang LE