From MobileRobots Research and Academic Customer Support

Server Information Packet

To update client programs on the state of the robot, the robot firmware sends a packet to the client periodically. This packet is called the Server Information Packet, Standard Information Packet, or SIP. (It also occasionally called a "motor packet".) By default, it sends the SIP every 100ms (10hz), though this frequency can be changed in the firmware configuration parameters.

The format and contents of the SIP is described in the robot manuals in the "ARCOS" chapter.

New version of firmware sometimes add additional information to the end of the SIP, but remain otherwise compatible with all previous versions, and with all varieties of robot firmware.

The SIP contents include the robot position estimate (X, Y, Theta), current velocities (translational and rotational), battery voltage, motor stall state, bumper states (triggered or not), recent range data from built in sonar sensors, states of digital I/O ports (including some accessories such as the gripper), value read from the analog input port(s), and miscellaneous other state flags.

ARIA's ArRobot class is responsible for ultimately retrieving data out of the SIP. It does this automatically in its robot synchronization or task cycle (initiated by a call to run() or runAsync(). For details on the robot synchronization and task cycle, see the ARIA reference manual. ArRobot contains methods for accessing all of the information it has received from the SIP. (ArSonarDevice and ArBumpers also stores sonar and bumper data respectively, and implement the ArRangeDevice interface for obtaining sensor reading positions in the robot coordinate system.)