This morning I’m on the run, so I’ve started my morning with a hot cup of drip coffee from one of my old favorite coffee shops. Here in Seattle, you’re pretty much always within shouting distance of a coffee shop and with so many options it can border on overwhelming where to buy coffee. I’ve been a fan of Seven coffee roasters for years since I was living in the area. Now they’re a little farther out of the way for me, but when I’m in the area it’s worth a stop. Today I’ve got a cup of their Honolulu Hawaiian blend. It’s bright, floral, and most important for today – it’s a quick stop along my morning errands.
Over the past week I’ve been getting started with Robot Operating System (ROS) concepts. In general, ROS programs consist of the core package which tracks nodes, topics, services, and manages the parameter server. The individual executable components of code in a ROS system are known as nodes, and run their respective sets of methods to operate the components of a system. ROS nodes can communicate with each other either through topics or services. Services are similar to the familiar request/response concept we are familiar with through HTTP, allowing individual nodes to communicate with one another.
Topics make use of the publisher/subscriber model. The pub/sub model is a many-to-many communication bus which allows nodes to publish data to topics and all nodes subscribed to a specific topic will receive that data rather than the one-to-one request/response model. Topics are defined by the data type they transfer and publishers must adhere to the data type for the give topic, this may be primitive types or C-style structs. Through this model, a program can run on a central controlling computer and each node is able to independently operate its respective service whether it be an internal operation or running an external micro controller. This allows for additional nodes which make use of common data to be subscribe to the same topic to receive the same events. By using this paradigm, a system can scale up the number of nodes or repurpose data in an asynchronously running program. I’ve previously been aware of this communication paradigm, but never worked with it before. I’m looking forward to continuing to learn about it given its suitability for robotics and IoT devices.
