Echelon OpenLNS - Manual (Page 892)

OpenLNS Programmer's Reference 855
If a host-based device whose application is not running is
installed on the network, OpenLNS may or may not be able
to discover it. Whether OpenLNS can discover and register
the device depends on how much of the device's LonTalk
protocol stack is running at the time of the discovery.
Discovering a device involves first the actual discovery of the
device and then the registration of that device in the
database. The discovery service is always performed in the
foreground and the registration service may be performed
either as a background or foreground task. Select the type of
operation by setting the backgroundReg parameter to True or
False, as desired.
If backgroundReg is set to False, devices are registered in the
foreground as part of the discovery transaction, so the
method will not return until discovery is completed or
terminated. When the method completes, it returns the
number of discovered devices in the numDevicesDiscovered
parameter, and the newly registered devices may be accessed
in the Discovered.Uninstalled subsystem. If an error occurs
while registering a device, the method will return when one
of the following conditions is met: all discovered devices have
been registered, or 50 devices have been registered.
If backgroundReg is set to True, discovered devices are
registered in separate background transactions. In this case,
any error that occurs during the registration of one device
has no effect on the registration of any others. When the
method completes, numDevicesDiscovered again returns the
number devices discovered. Registration of those devices
proceeds asynchronously. As each device completes
registration, it appears in the Discovered.Uninstalled
subsystem. To limit resource usage during background
discovery, the Object Server limits the number of devices that
may be registered to 50. You can use the OnChangeEvent
event to track when the devices have been registered. The
event will be fired once for each device that is registered, so
you can assume the registration process has not completed
until the number of events fired matches the value of the
numDevDiscovered element.
When the DiscoverDevices method is halted by an error or its
background registration limit, and additional devices remain
to be registered, the Object Server's DiscoveryLimitedFlag
property is set to True. To ensure that all discovered devices
have been registered, the DiscoverDevices method must be
reinvoked. In particular, when registering devices in the
background (backgroundReg = True), this method must be
invoked repetitively until no further devices are discovered.
The repeat interval must be sufficiently long to allow the
server time to register all devices discovered during the
previous DiscoverDevices invocation.
When the DiscoverDevices call is made within an explicit
transaction (see StartTransaction) and foreground