Image Processing Reference
In-Depth Information
Application 1
Application 2
Event
Event
Service A
Service B
Service
call
Polling
Interface layer
Kernel
FIGURE .
Interprocess operations in Contiki.
This method is recommended to expand the kernel only, such as to support memory management.
Next, to add additional functionality to an application only, statical linking of specific libraries is
appropriate. hird, linking of dynamical libraries is the preferred method to add functionality to the
application depending on the current state. Dynamical libraries are loaded as services and there-
fore are processes, too. Hence, these processes can be accessed by all other applications as well. As
illustrated in Figure ., Contiki uses a service layer to provide applications access to the available
services.
12.3.8.3 Runtime Programming
During lifetime of a sensor network, reprogramming of node's software may be required at runtime
without recollecting nodes. TinyOS, for instance, allows reprogramming by using the bytecode inter-
preter MATÉ (see Section ..) which can be installed as one program on top of the OS. Contiki
does not need such an interpreter, instead, it provides loading and unloading of all kinds of pro-
cesses even drivers and, for instance, the communication stack, at any time. Therefore to support
OTA programming, a specialized protocol is defined.
12.3.8.4 Platforms
Contiki was developed as lightweight OS for sensor networks. Therefore, Contiki has a very small
memory footprint and uses all constraint processing resources as efficient as possible. Currently, the
system is ported to a lot of target systems, for instance, MSP and Atmel AVR.
DuetoContiki'smodularity,portingthesystemafectsonlysomeparts.hesepartsaretheboot-up
code, architecture-specific parts of the program loader, and device drivers. If multithreading should
be available on the target architecture, the stack switching code of the multithreading library has to
be adopted, too. But there is no need for changing the kernel and the service layer. Thus, porting
Contikitoanewtargettakesonlyafewhoursordays.
12.3.9 Sensor Web Enablement
The standards organization Open Geospatial Consortium Inc.
◯
R
(OGC) [] has published several
standards and specifications for geospatial and location-based services on the Web. his consortium
