Echelon OpenLDV User Manual download pdf (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.

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