Echelon Neuron C - Manual (Page 70)

58 How Devices Communicate Using Network Variables
mtimer tDelayedPolling;
/////////////////////////// Tasks //////////////////////
// NV update task -- handle update to lamp state
// Use the network variable’s value as the new state
// for the lamp
when (nv_update_occurs(nviLampState)) {
io_out(ioLED,
nviLampState.value && nviLampState.state
? LED_ON : LED_OFF);
}
when (reset) {
// set up timer for delayed power-up polling:
tDelayedPolling = 4ul * random(); // >= 1 second
... // other reset processing
}
when (timer_expires(tDelayedPolling)) {
poll(nviLampState);
}
Declaring an Input Network Variable as Polled
For Neuron-hosted applications, you cannot declare in input network variable as
polled; the Neuron C compiler issues an error message for polled input network
variables.
However, within a model file for a host-based application (such as for a
ShortStack, FTXL, or i .LON SmartServer application), you can declare an input
network variable as polled:
network input polled type netvar ;
For host-based applications, the application code is written in a language other
than Neuron C, and therefore the presence of the poll( ) function within the
application would not cause the compiler to adjust the device’s self-identification
data to allow the network tool to create the network variable binding
appropriately. Thus, within a model file, the declaration of the input network
variable is allowed to be declared as polled so that the ShortStack Micro Server,
FTXL LonTalk protocol stack, or i .LON SmartServer can allow the network
variable to be polled.
Declaring an Output Network Variable as Polled
To allow devices to receive network variable updates from other devices only at
specified times, declare the output network variable as polled:
network output polled type netvar ;
In this special case, the output network variable’s value is never propagated as a
result of its value changing. Instead, the output network variable’s value is sent
only in response to a poll request from a reader device, or if the propagate( )
function is called for that network variable.