As described in Using ROS through EEROS HAL you can directly map EEROS signal onto ROS messages through the EEROS HAL. The wrapper library EEROS-ROS is used to connect the EEROS HAL with ROS topics.
The EEROS HAL digital and analog inputs and outputs can be defined as usual in a JSON file. There are hundreds of different message types in ROS and it is possible to create custom types.

Because every message type has to be handled differently, only a few are supported by default.

But the wrapper library can easily be extended to support additional message types.

Chapter \ref{sectionImplementMsgType} describes how you can add a new ROS msg type to the library.

Table \ref{tableKeyValueEeros} shows the most important key-value pairs for using the HAL with ROS.

\begin{table}[]

\centering

\caption{Most important key-value pairs for ros-eeros}

\label{tableKeyValueEeros}

\begin{tabular}{@{}lll@{}}

\toprule

Key & Typical value & Description
\midrule

library & libroseeros.so & Wrapper library for ROS

devHandle & testNodeHAL & ROS node created by HAL

type & AnalogIn / AnalogOut / DigIn / DigOut & Type of input / output

additionalArguments & 'see next table' & 'see next table'
\bottomrule

\end{tabular}

\end{table}

The \textit{additionalArguments} are special arguments which are parsed in the wrapper library \textit{ros-eeros}.

These arguments contain additional information which are necessary to communicate with a ROS network.

All arguments are separated with a semicolon.

The available arguments are listed in table \ref{tableAdditionalArgumentsEeros}.

An example for an additional argument could be:

\begin{snugshade*}

\textit{\char“22additionalArguments\char”22: \char“22topic=/testNode/TestTopic3; msgType=sensor\_msgs::LaserScan;

dataField=scan\_time; callOne=false; queueSize=100\char”22,}

\end{snugshade*}

Table \ref{tableAdditionalArgumentsEeros} shows all currently available \textit{additionalArguments}.

\textbf{Topic} and \textbf{msgType} are mandatory arguments.

\begin{table}

\centering

\caption{Additional arguments specific for ros-eeros}

\label{tableAdditionalArgumentsEeros}

\begin{tabular}{@{}lll@{}}

\toprule

Key & Typical value & Description
\midrule

\textbf{topic} & /testNode/TestTopic1 & Topic to listen / subscribe

\textbf{msgType } & sensor\_msgs::LaserScan & ROS message type of topic

dataField & scan\_time & Desired data member of message

callOne & true & Oldest, not yet fetched message is fetched

callOne & false & Newest available message is fetched

queueSize & 1000 & Size of buffer; queueSize=1000 if omitted

useEerosSystemTime & fals & Use system time or timestamp of received msg
\bottomrule

\end{tabular}

\end{table}

In table \ref{tableImplementedMsgTypes} are all currently implemented message types and associated data fields.

If your desired message type is not implemented yet, you can easily implement it yourself.

See chapter \ref{sectionImplementMsgType} for a guide to implement additional message types and data fields in \textit{ros-eeros}.

\begin{table}[]

\centering

\caption{Currently implemented message types in ros-eeros}

\label{tableImplementedMsgTypes}

\begin{tabular}{lll}

\cline{2-3}

HAL type & msgType & dataField
\cline{2-3}

AnalogIn & std\_msgs::Float64 & -

        & sensor\_msgs::LaserScan    & angle\_min       \\

        &                            & angle\_max       \\

        &                            & angle\_increment \\

        &                            & time\_increment  \\

        &                            & scan\_time       \\

        &                            & range\_min       \\

        &                            & range\_max       \\

AnalogOut & std\_msgs::Float64 & -

        & sensor\_msgs::LaserScan    & angle\_min       \\

        &                            & angle\_max       \\

        &                            & angle\_increment \\

        &                            & time\_increment  \\

        &                            & scan\_time       \\

        &                            & range\_min       \\

        &                            & range\_max       \\

DigIn & sensor\_msgs::BatteryState & present

DigOut & sensor\_msgs::BatteryState & present
\cline{2-3}

\end{tabular}

\end{table}

You can find a complete example, including a *.json file, in the eeros framework (/examples/hal/Ros*).

\subsection{How to use}

Refere to the documentation of the EEROS HAL\footnote{http://wiki.eeros.org/eeros\_architecture/hal/start?s[]=hal} and check the example in the eeros framework (/examples/ros).

First initialize the HAL in your main function:

\lstset{language=c}

\begin{lstlisting}

…

int main(int argc, char **argv) {

...

// HAL

// ////////////////////////////////////////////////////////////////////////

HAL& hal = HAL::instance();

hal.readConfigFromFile(&argc, argv);

...

\end{lstlisting}

Add the header file to your control system:

\lstset{language=c}

\begin{lstlisting}

#include <eeros/hal/HAL.hpp>

\end{lstlisting}

You can now declare \textit{PeripheralInputs} and \textit{PeripheralOutputs}:

\lstset{language=c}

\begin{lstlisting}

PeripheralInput<double>		analogIn0;

PeripheralInput<bool>		digitalIn0;

PeripheralOutput<double>	analogOut0;

PeripheralOutput<bool>		digitalOut0;

\end{lstlisting}

Call the constructor of the peripheral IOs with the \textit{signalID} used in the *.json file

\begin{lstlisting}

class MyControlSystem {

public:

MyControlSystem(double ts, ros::NodeHandle& rosNodeHandler):

	dt(ts),

	...

	analogIn0("scanTimeIn0"),		// argument has to match signalId of json

	digitalIn0("batteryPresent0"),

	analogOut0("scanTimeEchoOut0"),

	digitalOut0("batteryPresentEchoOut0"),

	...

}