Applications are built by creating filters and arranging filter chains both on the motes and the microservers.

On the mote end, data is generated at the Sampler and is pushed down through the stack of filters down to the Packetizer and finally to the radio. This data is then received by the microserver, unpacketized and pushed through the microserver's filter stack and made available to the end-user through a device file.

Since filters are created to work both on the motes and the microservers, the user, at runtime, can change where data is processed. For example, if the user wants all the data collected by the mote to reach the microserver, the mote can be instructed, at run time, to stop filtering. All data collected will then be sent to the microserver where the local filters can analyze the data.

All VanGo applications are configured in a constants file called SnackConstants.h and a nesC application configuration file.

-rw-r--r-- 1 alex users 7634 Jun  5 15:31 AuricleDemo.nc
-rw-r--r-- 1 alex users  427 May 23 21:38 Makefile
-rw-r--r-- 1 alex users 3490 May 31 11:22 SnackConstants.h

The SnackConstats file holds all variables that describe the filters and the core framework modules; they are all of the modifiable variables in the application - most can be changed during runtime by sending a control message. The values in the configuration are the defaults and the filters are initialized with these values at start up. Usually, once an application filter stack is setup, it is easy to change the way an application works by flipping the configuration defaults. For example, it is possible to disable filters in the stack by changing the enable values in the configuration file; no nesC code needs to be modified.

The main nesC application configuration file (AuricleDemo.nc) is used mostly to build the filter stack. A filter stack is built by wiring a FilterControl interface of one filter to another.

...
FastSamplerSeparateC.Filter_u0 -> FragmentM.Filter_p;
FragmentM.Filter_u -> AverageM.Filter_p;
AverageM.Filter_u -> GateM.Filter_p;
GateM.Filter_u -> ZeroCrossingM.Filter_p;
ZeroCrossingM.Filter_u -> AdpcmM.Filter_p;
AdpcmM.Filter_u -> PacketizerM.Filter_p;
...

Along with the filter stack, the configuration file also contains the wirings that pull together the VanGo framework modules. For most VanGo users, only the filter stack will be of interest.