DESCRIPTION
ros2_control turns robot-description metadata into a typed hardware contract.
Hardware plugin
The hardware element identifies the plugin class that implements the component.
Command interfaces
Declare values controllers may command, such as position, velocity or effort.
State interfaces
Declare values hardware exposes back to controllers and broadcasters.
Sensors
Group read-only state interfaces for hardware sensors.
GPIO
Represent additional digital or analog hardware interfaces.
Transmissions
Describe actuator-to-joint mappings when the hardware component uses them.
RUNTIME
The XML is configuration; the plugin performs read and write.
01URDF + ros2_control→
02HardwareInfo→
03Hardware plugin→
04read()→
05Controllers→
06write()→
07Physical device
Official ros2_control tutorials describe a real-time read/update/write loop. Parsing a hardware definition is not the same event as commanding hardware.