Echelon LonTal Stack - Manual (Page 124)

112 Developing a LonTalk Stack Device Application
LonNvdSegNodeDefinition segments, but not for the application-defined
LonNvdSegApplicationData segment. Instead, the LonTalk host stack calls
the LonNvdGetApplicationSegmentSize() callback handler function in step 1
above, and the LonNvdSerializeSegment() callback handler function during
step 3 above when it processes the LonNvdSegApplicationData segment.
Both of these callback handler functions are generated by the LonTalk Interface
Developer utility.
The LonTalk host stack uses a low-priority operating system task or thread
(typically lower than the application task) to write NVD to persistent memory.
By using a low-priority task or thread, writing NVD should not block the running
of the application or the LonTalk host stack. In addition, LonTalk host stack
ensures that these NVD-management functions are never called by more than
one task or thread at a time.
The application can update configuration network variables (CPNVs) and user
files directly, without the LonTalk host stack’s knowledge. The application must
inform the LonTalk host stack when this occurs so that the LonTalk host stack
can manage the write transaction. Thus, the application should call the
LonNvdAppSegHasBeenUpdated() function to initiate an NVD transaction
for the application segment.
Tasks Performed by a LonTalk Stack Application
The main() function of a LonTalk Stack application typically performs only the
following actions:
1. Creates one or more operating system contexts (tasks or threads)
2. Starts the operating system (if it is not already started)
Within one of the newly created tasks, the application life cycle includes two
phases:
• Initialization
• Normal processing
The initialization phase of a LonTalk Stack application includes a call to the
LonInit() API function to initialize the LonTalk host stack and the Echelon
Smart Transceiver or Neuron Chip. The initialization phase defines basic
parameters for L
ON W ORKS network communication, such as the communication
parameters for the physical transceiver in use, and defines the application’s
external interface: its network variables, configuration properties, and
self-documentation data. Successful completion of the initialization phase causes
the Echelon Smart Transceiver or Neuron Chip to leave Quiet mode, after which
it can send and receive messages over the network. During the initialization
phase, the application also creates at least one operating system event (or other
protected shared resource).
During normal processing, which is often implemented within an infinite loop,
the application waits for an operating system event whenever it is not busy.
When the event occurs, the application calls the LonEventPump() API function
to process LonTalk Stack events. This function then calls event handler
functions (such as LonNvUpdateOccurred() or LonNvUpdateCompleted()).
The following sections describe the tasks that a LonTalk Stack application
performs during its life cycle.