This example device service illustrates a mechanism for accepting actuation commands within the EdgeX device model. It allows messages to be written to a terminal at specified positions.
When the service is run, it will clear the terminal in which it is running, and wait for commands. The only command implemented takes as its parameters a string to be written to the terminal, and the x and y coordinates at which to write it.
Building the device service requires the ncurses development library to be
installed on the system.
The environment variable CSDK_DIR should be set to a directory containing the C SDK include files and libraries.
Set LD_LIBRARY_PATH to $CSDK_DIR/lib
gcc -I$CSDK_DIR/include -L$CSDK_DIR/lib -o device-terminal device-terminal.c -lcsdk -lncurses
A device profile for the simulated device is provided in the res directory. This will be uploaded to core-metadata by the device service on first run.
The supplied configuration file res/configuration.toml includes definitions for a single terminal device. No protocol properties are defined for the device - the example runs on the basis of one device per service instance.
An EdgeX system containing at least a database and the core-data and core-metadata services must be running. The configuration file must be edited to reflect the locations of the core-data and core-metadata services.
./device-terminal -c res
Note that for this example the logging level is set to WARNING to keep the display clear in normal operation. To display a message on the terminal,
curl -X PUT -d '{"Message":"Hello World", "Xposition":"35", "Yposition":"12"}' 0:59999/api/v2/device/name/Terminal/WriteMsg
The service uses the defaulting mechanism in deviceCommands in order to pass the name of the operation being requested to the implementation. The defaultValue field in a resource operation sets a value to be used if one is not supplied in the PUT request.
The isHidden field is used to prevent the individual deviceResources being accessed directly via the core-command service.