Echelon OpenLDV - Manual (Page 116)

108 Extending xDriver
The events shown in Figure 17 that occur within the LNS application represent
a typical LNS application that registers for uplink session event handling. Your
application can vary from these steps.
In addition, the events that occur within the lookup extension component in the
flow chart represent the minimal tasks that a lookup extension component must
perform during an uplink session. This flow chart refers to the methods that you
can use when programming your custom lookup extension component. For more
information about these methods, see Appendix C, Custom Lookup Extension
Component Programming, on page 161.
Session Control Object
The SCO is created at the beginning of an xDriver session. During its creation,
the lookup key of the RNI involved in the session is filled into the SCO. The SCO
is then passed to the lookup extension component, which extracts the lookup key
from the SCO and uses it to access the xDriver database. The lookup extension
component then fills in the rest of the SCO with additional information required
to initiate the connection.
Table 35 describes the fields that are filled into the SCO, and how the lookup
extension uses them. If you use a database management system as your xDriver
database, you must create a custom lookup extension component to access the
database and fill in the SCO fields described in Table 35.
Creating a Custom Lookup Extension in C++ on page 113 and Creating a Custom
Lookup Extension in Visual Basic on page 125 describe how to create the
framework for a custom lookup extension component using Microsoft Visual
Studio 2008. Appendix C, Custom Lookup Extension Component Programming,
on page 161, describes the xDriver methods that you can use to read and write to
each of these SCO fields. The appendix also contains field type constraints to be
used when creating a custom database table.
The lookup extension component has read/write access to all of the fields in
Table 35, and the lookup extension component is required to set each field
unless otherwise noted.
Table 35. Session Control Object
Field Description
Session Control Object ID The SCO ID is a unique, read-only, 32-bit field that is filled in
when the SCO is created, before the first call to the lookup
extension. It can be used to identify the SCO.
Downlink Lookup Key The downlink lookup key is an ASCII string (105 characters
maximum) that is used by the lookup extension component to
access the xDriver database. This field is specified as part of the
network interface name for an RNI. For more information about
the xDriver network interface naming convention, see Downlink
Sample Applications on page 138.
This field is specified in the network interface name of the RNI
during a downlink session, and is read-only during downlinks.
This field must be filled in during uplink sessions.