Image Processing Reference
In-Depth Information
L-PDU length is bytes while for FlexRay the maximum L-PDU length is bytes.
AUTOSAR COM ensures a local transmission when both components are located on
thesameECU,orbybuildingsuitedobjectsandtriggeringtheappropriateservicesof
the lower layers when the components are remote. This scheme enables the portability
of components and hides their distribution. The transformation from signals to I-PDU
and from I-PDU to signals is done according to an offline generated configuration. Each
I-PDU is characterized by a behavioral parameter, termed “Transmission Mode” whose
possiblevalueis“direct”indicates(thesendingoftheI-PDUisdoneassoonasatriggered
signal contained in this I-PDU is sent at application layer), “periodic” means (the send-
ing of the I-PDU is done only periodically), “mixed” (the rules imposed by the triggered
signals contained in the I-PDU are taken into account, and additionally the I-PDU is sent
periodically if it contains at least one pending signal) or “none” (for I-PDUs whose emis-
sion rules depend on the underlying network protocol, as e.g., FlexRay; no transmission
is initiated by AUTOSAR COM in this mode).
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N-PDU is built by the basic components CAN TP (Transport Protocol) or FlexRay TP.
It consists of the data payload of the frame that will be transmitted on the network and
protocol control information. Note that the use of a transport layer is not mandatory and
I-PDUs can be transmitted directly to the lower layers (see Figure .).
The RTE implements the AUTOSAR MW interface and the corresponding services. In particular,
the RTE handles the “implicit/explicit” communication modes and the fact that the communication
involves “events” (queued) or “data” (unqueued). he AUTOSAR COM component is responsible for
several functions: on the sender side, it ensures the transmission and notifies the application about its
outcome (success or error). In particular, AUTOSAR COM can inform the application if the trans-
mission of an I-PDU did not take place before a specified deadline (i.e., deadline monitoring). On
the receiver side, it also notifies the application (success or error of a reception) and supports the
filtering mechanism for signals (dispatching each signal of a received I-PDU to the application or
to a gateway). Both at the sending and receiving end, the Endianness conversion is taken in charge.
An important role of the COM component is to pack/unpack “signals” into/from “I-PDUs.” Note
that, as the maximal length of an I-PDU depends on the underlying networks, the design of a COM
component has to take into account the networks and therefore it is not fully independent of the
hardware architecture. The COM component has also to determine the points in time where to
send the I-PDUs. his is based on the attributes Transmission Mode of an I-PDU and on the attribute
Transfer Property of each signal that it contains. Table . summarizes the combinations that
are possible. Note that the none Transmission Mode is not indicated in this table, in that case the
transmission is driven by the underlying network layers.
TABLE .
Transmission Mode of an I-PDU versus Transfer Property of Its Signals
Transfer Property of
the signals
All the signals in the I-PDU are
triggered
All the signals in the I-PDU are
pending
At lease one signal is triggered
and one is pending in the I-PDU
Transmission mode
of the I-PDU
Direct
The transmission of the I-PDU
is done each time a signal is
sent
This configuration could be
dangerous: if no emission of
triggered signals occurs, the
pending signals will never be
transmitted
Periodic
The transmission of the I-PDU
is done periodically
The transmission of the I-PDU
is done periodically
The transmission of the I-PDU is
done periodically
Mixed
The transmission of the I-PDU
is done each time a signal is
sent and at each period
The transmission of the I-PDU
is done periodically
The transmission of the I-PDU is
done each time a Triggered sig-
nal is sent and at each period
