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Chapter 4. Implementation 49

come from the interface converter service or the "send usb" and "send wlan"-command.

Raw output: Emits all incoming data from the gateway. Equals an addition of the topics other

output and protocol output, except that the HA messages are outputted in their raw string

format.

Raw input: sends all data directly to the gateway without further processing.

Both MiniCtrl and WiﬁCtrl can be conﬁgured by special conﬁguration commands (see reference

card on 79); therefore a mechanism must exist, which ensures that the gateway assumes a particular

state during the start-up of the nodes. This algorithm is called start-up script and sends commands

successively and with a small delay between each from a command list. That list can be passed

as a command line parameter or loaded with a launch ﬁle.

Now that we have learnt the basics functions of the gateway driver, I will go into further detail.

Figure 4.12 depicts the internal structure of the node.

Qextserialport

QTcpSocket

serial

tcp

gateway rosnode

serial

tcpWLAN

USB

driver

main

protocol

out

protocol

connect

ros

gateway driver

thread 1 thread 2

Figure 4.12.: The internal structure of the gateway driver. Each block represents an object within

the program, in which the green objects are third-party classes. The diﬀerent objects

communicate through signals and slots as well as by method calls. The driver blocks

are drivers of the operating system, which convert the serial stream to USB and

distribute the TCP packages over WLAN.

When starting the gateway driver, the main function initialises all objects, connects to the gateway

and starts the Qt event systems, which is used for the signal/slot mechanism. Most of the

intercommunication is done via signals and slots, as they are event driven and easy to program.

This is useful, because they are thread safe and the program is divided in two threads, one for the

ROS related functions and one for all other functions. This separation makes it possible to run

the ROS main loop in a separate thread, so that the rest of the program is not blocked during

service calls. As mentioned before, the gateway can be connected via serial interface or TCP

connection. The serial class is used for serial connection. It inherits from the third-party library

QextSerialPort and adds a receiving and transmitting buﬀer, as well as a ﬁltering algorithm, which

assembles fragmented input streams. As the WiﬁCtrl lost its full real time capability due to use of

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