+After starting the communication with the Roomba by sending the \cmd{Start}
+command, the robot is in a state called \definition{Passive mode}. In this mode,
+the user cannot control the robot by himself, but the internal logic defines
+icants behaviour. However, the user is able to read the internal sensors. The
+\ac{ROI} then allows the user to set the Roomba into two different modes:
+\begin{itemize}
+ \item In \definition{Safe mode}, the Roomba monitors the wheel drop, cliff
+ and internal charger sensors, and reverts into Passive mode if safety
+ conditions occur, so the Roomba is not harmed.
+ \item In \definition{Full mode}, the user has full control over the Roomba,
+ and has to take care not to harm the Roomba by evaluating the wheel drop,
+ cliff and internal charger sensors by himself.
+\end{itemize}
+
+In particular, every command is assigned an \ac{opcode} of one byte length,
+followed by a fixed amount of bytes as parameters which depend on the opcode.
+For example, to start the communication with the Roomba, the \cmd{Start}
+command has to be sent, which has the \opcode{0x80} and takes no parameters. The
+\cmd{Safe} command to put the Roomba into safe mode has \opcode{0x83}, and like
+the \cmd{Full} command with \opcode{0x84}, it takes no parameters.
+
+For example, to start the communication with the Roomba and set it into Safe
+mode, one would send the following bytes over the serial interface:
+\begin{verbatim}
+0x80, // Start command
+0x83 // Safe command
+\end{verbatim}
+The, additional commands can be sent over the \ac{ROI}, like actuator commands
+for controlling the Roomba's driving behaviour.
+
+\paragraph{Actuator commands}
+The \ac{ROI} specifies various actuator commands to control the Roomba's wheels,
+brushes and \ac{LED} displays, and let the Roomba play tunes. However, the
+central command needed for the experiments in thie thesis is the \cmd{Drive}
+command, \opcode{0x89}, which takes 4 additional bytes as parameter: the first
+two bytes specify the velocity that the Roomba's centerpoint should travel with
+while driving, and the third and fourth bytes specify the radius of the arc the
+Roomba's centerpoint should describe. The Roomba then calculates the required
+right and left wheel velocities internally without further interference of the
+user.
+
+The velocity is interpreted in mm/s, the value can range from -500~mm/s to
+500~mm/s, with negative values implying backwards movement. The radius is
+interpreted in mm, ranging from -2000~mm to 2000~mm. Negative values make the
+Roomba turn toward the right, whereas positive values make it turn toward the
+left. There are also four special values for the radius: \magicnumber{1} makes
+the Roomba turn on the spot in counter-clockwise direction, \magicnumber{-1}
+makes the Roomba turn on the spot in clockwise direction, and
+\magicnumber{0x7fff} and \magicnumber{0x8000} make him drive straight.
+
+For example, to drive straight with a velocity of 1000~mm, one would send the
+following bytes over the serial interface:
+\begin{verbatim}
+0x89, // Drive command
+0x03, 0xe8 // parameter velocity: 0x03e8 == 1000
+0x80, 0x00 // parameter radius: special value "straight"
+\end{verbatim}
+
+A little disadvantage of the \ac{ROI} \cmd{Drive} command is that the robot is
+modeled as a state machine. In the previous example, the Roomba would keep on
+driving until it runs out of energy, or a safety condition occurs which causes
+the Roomba to revert into Passive mode, or a new \cmd{Drive} command with the
+velocity parameter set to zero is sent. Thus, if the user wants to drive a
+specific distance, he has to calculate the time the robot needs to travel that
+distance, measure the time, and stop the robot after that time interval has
+passed. When using incorrect clocks, or when using inaccurate timers, this can
+lead to errors in movement. Because of that, it is appropriate to monitor the
+Roomba's movement, for example with its internal sensors.
+
+\paragraph{Input commands}
+The Roomba~500 series features a total of 49 different sensor values. Among the
+sensors mentioned above, there are also some internal values concerning battery
+charge, capacity, and temperature, motor currents, and even some more (or less)
+useful variables like the characters read from the infrared remote control, the
+current \ac{ROI} mode or the currently playing song. Nevertheless, there is
+also the possibility to query the travelled distance, the turned angle and the
+internal encoder counts ("`ticks"') for the left and right wheel. Each sensor
+value is 1 or 2 bytes long and is assigned a specific \definition{packet ID}.
+Some packet IDs also describe groups of multiple sensor values sent together.
+
+Sensor values can be retrieved either by explicit polling or by enabling a
+stream of values that is sent every 15~ms. Explicit polling works through the
+\cmd{Sensors} command (\opcode{0x8e}), which takes the packet ID of a single
+sensor as parameter, or through the \cmd{Query List} (\opcode{0x95}) command,
+which takes multiple packet IDs headed by the total number of requested packets
+as parameter. Both of these functions send back the requested values directly.
+
+By using the \cmd{Stream} command (\opcode{0x94}), it is possible to receive
+the requested sensor values every 15~ms. This is very convenient for real-time
+behaviour, when the sensor values have to be evaluated very often. As the
+\cmd{Query List} command, the \cmd{Stream} command takes the total number of
+packet IDs followed by the requested packet IDs as parameter. It sends back the
+sensor values in packets using the following format:\\
+\verb|0x13|, $n, p_1, v(p_1), p_2, v(p_2), \ldots, p_n, v(p_n), c$\\
+where:
+\begin{description}
+ \item[$n$] is the number of bytes sent back, excluding $n$ and $c$,
+ \item[$p_i$] is a requested packet ID, $i = 1, \ldots, n$
+ \item[$v(p_i)$] is the value of the packet with the packet ID $p_i$
+ \item[$c$] is a checksum, with
+ $\sum_{i=1}^n\left(p_1 + v(p_1)\right) + c + n \equiv 0 \mod 256$
+\end{description}
+
+Example: The following byte sequence requests data from the left cliff
+signal (packet~ID \magicnumber{0x1d}) and virtual wall sensor (packet~ID
+\magicnumber{0x0d}):
+\begin{verbatim}
+0x94, // Stream command
+0x02, // parameter: 2 packets following
+0x1d, 0x0d // parameter: request packets 0x1d and 0x0d
+\end{verbatim}
+
+The Roomba then returns the following bytes every 15~ms:
+\begin{verbatim}
+0x13, // Header byte
+0x05, // 5 bytes following, except checksum
+0x1d, // Packet ID 0x1d following
+0x02, 0x19, // Data for Packet ID 0x1d (2 byte)
+0x0d, // Packet ID 0x1d following
+0x00, // Data for Packet ID 0x0d (1 byte)
+0xb6 // checksum: 0x5 + 0x1d + 0x2 + 0x19 + 0xd + 0x0 + 0xb6 = 256
+\end{verbatim}
+
+In our setup, an iRobot Roomba~530 is used as an instance of an autonomous,
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