The Hardware Abstraction Layer provides an interface between the robot control system and the hardware of the robot. As we do not have any real output we will use a simulator, see Simulator. The system in this example uses inputs and outputs.

In the EEROS library you will find a directory with examples. For this example see HalTest1.cpp.

Open a shell in the build directory of your EEROS library and run

$ ./halTest1 -c HalTest1Config.json

This examples creates a small control system with a couple of peripheral input and output blocks as shown below.

Control system of the test program

The dashed lines denote the feedback of the signals by the simulator.
The main sequence alters the values on digital and analog outputs periodically. A separate periodic task logs the digital and analog inputs.

• The state on the digital output 0 is reflected by the simultor to the digital input 0. The control system connects this input to the digital output 1, which in turn is reflected by the simulator to digital input 1. However, the second reflection is inverted and we get the logical inversion of digital output 0. The value of digital input 0 changes every 5 seconds.
• A constant value is output to analog output 0 and 2. These values change every 10 seconds. Both are reflected onto analog inputs 0 and 2, respectively.

A peripheral output block delivers a signal to external hardware. Its signal value can be accessed with a get method, see line 41 in the comment in the example code in HalTest1.cpp.

Alternatively the signal in the HAL could be accessed by getting an reference to the corresponding output block with

auto digOut = hal.getLogicOutput("dOut0", false);  // line 37

The signal value can then be logged with block with

log.info() << digOut->get(); // line 42

You have to make sure to access the output with non-exclusive rights, because the control system already has a handle to it, see line 25 in halTest1.hpp. Likewise, the control system must access the same output in the same fashion.