wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

LonWorks 41-7
• Network management and diagnostic messages
These messages are used for the node configuration, including the setting of the logical addresses
(domain, subnet, node ID), writing to EEPROM (for application loading), and setting of bindings.
Router configuration messages belong to this group, too.
• Generic message passing
Applications can create and send any messages, including the above-specified ones. With the help
of application-specific message codes, own application-specific protocols can be implemented.
41.4 the Application Layer Programming Model
User applications for Neuron Chips are programmed in Neuron C, an extended ANSI C dialect. Since
applications are event based, Neuron C contains a construct called task, which is called whenever an event
has occurred or a condition is fulfilled. The event or condition is defined by a when clause. Events are,
for example, changes of network variable inputs (nv _ update _ occurs), the expiration of timers
(timer _ expires), the changing of I/O pins (io _ changes), or the reset event, which is called
after a reset. The following listing shows a simple application in Neuron C, which controls the state of a
LED using a network variable.
network input SNVT _ switch nviSwitch;
IO _ 0 output bit ledOutput; // specifies LED output
#define LED _ ON 1
#define LED _ OFF 0
when (reset)
{
io _ out(ledOutput, LED _ OFF);
}
when (nv _ update _ occurs(nviSwitch) )
{
// set LED according to NV value
if (nviSwitch.state == 1)
io _ out(ledOutput, LED _ ON);
else
io _ out(ledOutput, LED _ OFF);
}
The first two lines declare an input network variable named nviSwitch and an output bit object
using I/O pin 0. After that, two tasks are defined by when clauses. The first one is called after the reset
of the node and sets the output pin to a defined state (LED off). The second task is called when the
above-declared network variable is changed externally. Since nviSwitch has the structured type
SNVT _ switch, the concrete switch state is taken by the appropriate structure member. According to
the state value, the LED is switched on or off.
As shown in the example, special directives declare network variables and I/O objects. Further directives
are used for configuration parameters, function objects, and other node-specific properties.
The interface between the Neuron C program and the application layer of the Neuron Chip is offered
as a set of library functions. Important functions are implemented directly in the firmware. For example,
there are functions to process application-specific messages, for the network management of the
node itself, and for accessing the I/O objects. Other little-used functions, like floating point arithmetic
functions, are linked to the application image by the Neuron C linker, if required.
By running the Neuron C compiler, two kinds of files are created: First, application images contain
the compiled code, which is loaded to the node later, and second, the associated external interface
© 2011 by Taylor and Francis Group, LLC