Civil Engineering Reference
In-Depth Information
4.2.2.5
Application Abstraction Layer
The highest layer of the AUTOSAR-layered architecture is the interface to the appli-
cation. This application abstraction layer is the only interface of an AUTOSAR ap-
plication to the AUTOSAR basic software. No AUTOSAR application shall access
functions from the basic software direct. Out of the application perspective, there are
no tasks or interrupts anymore and basic software interfaces do not exist. This high-
est layer will be implemented only by one software module: the AUTOSAR RTE.
The RTE implements the connection of all communication paths and the ab-
straction of the runtime management. An AUTOSAR compliant application—
application software component—implements a software function. This application
software component consists out of a formal description in XML, the Software
Component Description (SWC-D) and the implementation in C source code. The
RTE itself will be generated with XML input data of the ECU configuration and all
the application software component descriptions. The API of the RTE depends on
the software components, their signal names and internal structure. The RTE is the
implementation of the virtual function bus (VFB), which is the core element of the
AUTOSAR architecture.
The VFB is the communication medium for all functions and provides sender/
receiver or client/server communication methods. In the world of the VFB, it is
not relevant where the function is executed and how the data are transported. The
“mapping” of functions to ECUs is part of the system design process—the result of
this process is the system description. The path for the signals will be defined by
the distribution of the application software components to real physical ECUs. For
the application it is irrelevant how the data are transported; this will be done by the
configured basic software and the RTE. A signal could be a direct result of a digital
input line or it could be a part of a CAN message (Fig.
4.17
).
4.2.2.6
AUTOSAR Applications
AUTOSAR compliant applications are connected via the RTE to the basic software
platform. The API of the RTE provides many possibilities of designing an applica-
tion. In principle, the communication is running via “ports” and the activation of
runtime parts is done by the execution of the so-called “runnable entities”. The
communication ports can be of the type sender/receiver or client/server. The client/
server type represents the typical function call, which is needed to call, e.g. library
functions (e.g. mathematical functions). As already mentioned, the information
from where the RTE gets the data is part of the RTE configuration (which is part
of the ECU configuration). With this method it is possible to develop application
software and define later the final communication path for each input or output
signal. This is the basis for shifting application functions within the vehicle ECU
topology—one of the goals of AUTOSAR. An ECU is in future AUTOSAR systems
only one piece of the whole platform which host application software.
