status_aggregator package
status_aggregator is a ROS package responsible for aggregating diagnostic status messages of the system and publish them on the /diagnostics_agg topic.
Important Sources
By far the best explanation about ROS diagnostics, kudos to Nick Lamprianidis. source 01 source 02
Rationale
ROS diagnostics is a tool to monitor your system. In a nutshell, status messages of the system are published on the /diagnostics topic and are then categorized and published for easy monitoring on the /diagnostics_agg topic.
As you can guess, two separate components are needed for the final result: updater and aggregator. The former publishes diagnostic status messages on the /diagnostics topic, using tasks. While the latter subscribes the /diagnostics topic, aggregates and categorize the diagnostic status messages and publishes the results on the /diagnostics_agg topic, using analyzers.
Updater and task
A robot system pocesses multiple updaters, which are generally associated to some device (computer, motors, sensors, batteries). Each updater gets the relevant status information of a device through tasks, that function as an interface between an updater and a device. The sequence of operations is as follows: * Device send data into a task; * Updater forwards a status message to the task; * Task populates status message;
When the update receives all the status messages from all the tasks it manages, it publishes them to the /diagnostics topic. The information by now has no hierarchy, difficulting the monotorization of the data.
NOTE: In our stack we discarded the use of the tasks, and directly populate the statuses messages in the devices.
Here is where Aggregator plays an important role.
Aggregator and analyzer
Aggregator comes to fathom out the messy output of the updaters. Basically it collects, categorizes, and groups the status messages from all the updaters of the system. It does so by using analyzers. Each status message received by the aggregator is forward to all of the analyzers it manages. The status messages are only analyzed if its name matches some criteria of one of the analyzers. The aggregator is then responsible to request a report from each analyzer and publish it on the /diagnostics_add topic. The report is just a list of status messages, one for each status item that the analyzer is responsible for, and one for the parent level that summarizes the state of its children statuses.
Package Content
Code documentation
Using status_aggregator
Requirements
- ROS diagnostics
- Information on /diagnostics topic