Echelon OpenLDV - Manual (Page 151)

OpenLDV Programmer’s Guide 143
be called from the Timer1_Timer() function after the next timer control interval
expires. The StartButton_Click() function opens the network that requested
connection in independent mode, and enables monitoring of the network variable
monitor set for that network. It also calls the ReleasePendingUpdates method
to release the monitor-point update events that have been withheld since the
session began.
The application then receives the monitor-point update event that caused the
uplink session request (for example, an alarm). Upon receiving a monitor-point
update event, the m_cOS_OnNvMonitorPointUpdateEvent() function is
called automatically. This function saves all information associated with the
monitor-point update event publicly, and sets a flag to True to indicate that a
monitor-point update has been received. This flag causes the
DisplayMP_Click() function to be called from the Timer1_Timer() function
after the next timer control interval expires, eliminating the need for any calls
from within the event handler. The DisplayMP_Click() function displays all
information saved for the monitor-point update event. It also sets a flag to True
to end the current uplink session.
When this flag is True, the StopButton_Click() function is called from the
Timer1_Timer() function after the next timer control interval expires. The
StopButton_Click() function disables the monitor point and monitor set for the
open network, and the network is closed. The application continues to listen for
requests for connection, and handles them in this fashion, until the application is
closed.
Important: A network interface could reset after receiving an alarm event, but
before the event has been propagated to the LNS Server, causing the event to be
lost. To prevent this loss, your applications must resend each monitor-point
update at short intervals until receipt of that event is confirmed, especially for
alarm applications. This technique results in reliable performance, and ensures
that no monitor point update events are lost before they are processed by the
LNS application.
For more information about any of the LNS commands used in this programming
sample, see the LNS Programmer’s Guide.
Dim m_cCurNet As LcaNetwork
Dim m_cMyVni As LcaAppDevice
Dim m_cMS As LcaMonitorSet
Dim m_gDP As LcaDataPoint
Dim m_gbInMP As Boolean 'Use the monitor point update event
'flag to track whether a monitor point
'update event has been received.
Dim m_gbInUplinkOpen As Boolean 'Use the uplink open flag to track
'whether an uplink session is currently
'being handled by the application.
Dim m_gbInUplinkClose As Boolean 'Use the uplink close flag to track
'whether the most recent uplink session
'handled by the application has been
'closed.
Dim m_szIncomingNetName As String 'This variable will be used to store
'the network name of a network
'requesting connection to the LNS
'server.
Private Sub Form_Initialize()
ExitButton.Enabled = True 'Enable the Exit button.
m_cOS.RemoteFlag = False 'Set the application access mode to