Echelon OpenLDV User Manual

Page 72

Sending and Receiving Messages with the OpenLDV API

For an uplink message (read from a network interface), the tag field indicates

the index into the receive transaction database for acknowledged, repeated

and request messages. When an OpenLDV application generates a response

to an uplink request message, it must save the tag value from the request,

and set the same tag value in the downlink response message.

priority

The priority field is set to indicate a message delivered with priority media

access, either uplink or downlink. When an OpenLDV application generates

a response to an uplink request message, it must save the priority attribute

from the request, and sets the response with the same priority. If the

network interface is configured without priority buffers, and a priority

request is received, the OpenLDV application sets the priority bit in the

response, but sends the response in a non-priority buffer.

path

The path field is set to 1 if the message should use the alternate path, and 0

if it should use the primary path. This feature is enabled only if the alternate

path bit is set. Alternate path is a feature of certain special-purpose mode

ORKS

transceivers, such as power line (PL) transceivers.

completion code

The completion code field is set for an uplink completion event. Completion

code events are returned to the OpenLDV application for every downlink

(niCOMM) network message sent:

•

The MSG_SUCCEEDS (1) value indicates that the message was

successfully delivered.

•

The MSG_FAILS (2) value indicates that the message failed to be

delivered.

•

Set the completion code field to MSG_NOT_COMPL (0) for

application layer buffers that are not completion events.

Messages sent to the network driver with the niNETMGMT network

interface command do not have associated completion events.

address mode

Set the address mode bit to 1 for an explicitly addressed downlink message,

and specify the network address field as a SendAddrDtl structure (see

SendAddrDtl on page 67).
Set the address mode field to 0 for an implicitly addressed downlink message,

in which case the network address field is ignored, although it must be

present. In this case, use the tag field as the index into the address table of

the Smart Transceiver or Neuron Chip in the network interface for the

destination address. For more information about the address table, see the

ISO/IEC 14908-1 protocol specification.
Set the address mode to 0 for downlink responses to uplink request messages

and network variable polls.
The address mode bit is ignored for local network management

(niNETMGMT) messages.