MODELING APPROACH FOR NETWORKED EMBEDDED

SYSTEMS WITH HETEROGENEOUS COMMUNICATION

Modeling Common Gateway Functionalities for Interconnection

Johannes Kl¨ockner, Marcus M¨uller, Wolfgang Fengler and Yixin Huang

Computer Architecture Group, Ilmenau University of Technology, P.O. Box 100565, Ilmenau, Germany

Keywords:

Model based design, Fieldbus, FlexRay, CAN, Building blocks, Network simulation, MLDesigner, Gateway.

Abstract:

This paper presents a method to create system level models of gateway facilities to combine embedded ﬁeld-

bus networks. Here automotive applications are used as representative with CAN and FlexRay. A strategy

is introduced to create gateway models, which provide high ﬂexibility in terms of reusability, replaceability,

extensibility and ﬂexibility. Todays systems often incorporate a very complex heterogeneous communication

structure with real time requirements. These characteristics have an inﬂuence on the system design process.

The goal of avoiding design errors in early development stages requires the validation on hierarchical func-

tional models of various abstraction levels using simulation based analysis prior to hardware design. A current

approach includes problem oriented system analysis. This approach is extended to analyze the system behav-

ior of heterogeneous embedded systems focusing on switching mechanisms. Here lies the challenge on the

connection of subsystems with distinct ﬁeldbuses realizing different paradigms. Regarding real time aspects

paradigm switches can be a source of errors in the system design.

1 INTRODUCTION

As a result of the increase in both system complexity

and the amount of incorporated functionality a single

embedded system has to be considered as a compo-

sition of several heterogeneous subsystems. Due to

this the intra-system networking of an embedded sys-

tem provides new challenges in system design. De-

veloping such complex systems requires a lot of plan-

ning and design decisions on a profound knowledge

of system behavior. The heterogeneity in a compound

system stems from differences in hardware, software

and subsystem architectures. In networked embedded

systems the communication is an important aspect.

Based on the complexity of systems and distributed

applications the amount of communication between

individual subsystems grows. Using communication

technologies with different paradigms, e.g. event or

time triggered, inﬂuence the system behavior.

The heterogeneity of large systems represents a

great challenge in the system design. This high grade

of variability complicates the development process.

Mistakes in early system design stages can negatively

inﬂuence the performance and development costs.

Avoiding these errors requires the validation on func-

tional models of various abstraction levels using sim-

ulation based analysis prior to hardware design.

To analyze the performance on system level

(Henia et al., 2005) use an approach based on a

scheduling analysis. A model based design approach

(Salzwedel, 2004) enables an efﬁcient top down de-

velopment of a complete system using hierarchically

composed building blocks, thus providing a high

grade of reusability and exchangeability.

Aim of the presented work is the extension of an

existing modeling approach studying networked em-

bedded systems to allow the modeling of heteroge-

neous networked systems in a common way and the

analysis of system behavior. It is based on the tool

MLDesigner (MLDesign Technologies Inc., 2007)

and fulﬁlls the requirements of a model based de-

sign approach allowing system analysis and devel-

opment. An example for a complex heterogeneous

networked embedded system is an automobile. It

is a system with a large amount of functionality,

real time requirements and distributed characteris-

tics. The complex communication infrastructure con-

tains several protocols with different paradigms, e.g.

FlexRay (FlexRay Consortium, 2005) and Controller

Area Network (CAN). The mentioned properties can

be found in a lot of systems belonging to areas en-

gaged with automation and control. This paper is

230

Klöckner J., Müller M., Fengler W. and Huang Y. (2009).

MODELING APPROACH FOR NETWORKED EMBEDDED SYSTEMS WITH HETEROGENEOUS COMMUNICATION - Modeling Common Gateway

Functionalities for Interconnection.

In Proceedings of the 6th International Conference on Informatics in Control, Automation and Robotics - Signal Processing, Systems Modeling and

Control, pages 230-233

DOI: 10.5220/0002207902300233

 SciTePress

organized as follows. Section 2 gives a short descrip-

tion of the used modeling tool. Section 3 introduces

related work and the basic modeling strategy. Section

4 describes the modeling concept. Section 5 presents

the drawn conclusions and a brief overview of further

development steps.

2 MODELING TOOL

Currently many tools exist, that realize model-based

design to support the development process. In this

work the tool MLDesigner by MLDesign Technolo-

gies, Inc. is used. The tool is dedicated to im-

proving the design process from early concepts to

implementation with mission and system level de-

sign. MLDesigner extends the Ptolemy project of

UC Berkeley (The Ptolemy Project, 2009) with mod-

eling paradigms. Different models of computation

so called domains are provided, e.g. discrete event

domain (DE) and ﬁnite state machines (FSM), syn-

chronous data ﬂow domain (SDF). In this work the

discrete event domain and ﬁnite state machines are

used. These two are well suited to modeling net-

worked embedded systems.

Now a short introduction to the terms of MLDe-

signer. The System is the top level element in the

modeling hierarchy. The building blocks can be

atomic blocks called Primitives, speciﬁed as FSM or

in C/C++ code, or hierarchical Modules. To commu-

nicate with their environment building blocks can use

linked variables or ports. Ports are represented as ar-

rows on the bounding box of a building block and are

interconnected by signal paths. So called Wormholes

allow the embedding of building blocks belonging to

different domains.

3 RELATED WORK

In (Kl¨ockner et al., 2008) a modeling strategy for net-

worked embedded systems is discussed exempliﬁed

by a top-down developed generalized FlexRay proto-

col model. The communication system is deﬁned as a

composition of three different elements: Host, Com-

munication Controller (CC) and Channel as shown

in Figure 1. The combination of a host and a CC is

called node. The corresponding protocol can be im-

plemented within the CC, e.g. synchronization, error

detection, message transmission and reception. In ad-

dition, the CC provides several services to the host

to be interfaced by its application. The application

of a node can be described within the host. The host

Figure 1: Basic Model Structure for networked embedded

systems (Kl¨ockner et al., 2008).

uses CC provided services to conﬁgure the CC, initi-

ate the sending and receiving operations and process

the received data. According to this the host contains

a specialized sublayer realizing the protocol related

access to the CC. At this point the division into differ-

ent functional layers is visible, the host describes the

functionality and the CC describes the type of com-

munication. Nodes are grouped to communication

clusters by connecting them to a channel.

The physical characteristics of the connection be-

tween nodes is described and modeled within a chan-

nel. On this level the physical delay of a transmission

is determined by the respective message data length

and a fault injection model simulates the transmission

errors caused by physical medium and environmental

inﬂuences.

The focus of the approach (Kl¨ockner et al., 2008)

lies on homogeneous communication systems. The

model structure intends the extension of the approach

to allow the modeling of heterogeneous systems.

4 GATEWAY MODEL

In order to provide concepts to monitor both the be-

havior of networked systems and the communica-

tion across different types of networks with differ-

ent speciﬁcations and protocols, a concept for a gate-

way model which provides high ﬂexibility in terms of

reusability, replaceability, extensibility and ﬂexibility

to connect different communication technologies in a

common way, is needed. Based on the model struc-

tures presented in (Kl¨ockner et al., 2008) (M¨uller,

2007) and the libraries developed in these works, the

creation of a customizable gateway module is possi-

ble. This allows the combination of heterogeneous

subsystems in order to analyze the overall system be-

havior. Regarding the system architecture presented

in Figure 1 a gateway is a special type of node. Nor-

mally a node is a combination of a host and a CC. A

node realizing gateway functionality is now a combi-

nation of several hosts, associated CCs and a Gate-

way Core. The basic gateway structure is shown in

Figure 2. The CCs contain the identical functionality

as described before. A common strategy to model an

MODELING APPROACH FOR NETWORKED EMBEDDED SYSTEMS WITH HETEROGENEOUS

COMMUNICATION - Modeling Common Gateway Functionalities for Interconnection

231

Host

(CC-Access)

Host

(Gateway Core)

Channel

(Network 1)

Channel

(Network 2)

Node_GW

Node_NW2Node_NW1

CC CC CC

Host

(CC-Access)

Figure 2: Extended Model Structure for networked embed-

ded systems.

application is not yet designed. Therefore the hosts

realize the speciﬁc sublayers to access the CCs. The

Gateway Core can be seen as an application of the

node providing the gateway base function. This con-

cept ﬁts the described modeling strategy. Anticipating

a more detailed model containing different applica-

tions in a node divided in several tasks it is possible

to extend this architecture to enable the analysis of the

system behavior including other effects, e.g. proper-

ties of task scheduling.

Gateway facilities handle the data exchange be-

tween heterogeneous computer networks. Normally,

they are designed to combine speciﬁed networks, and

fulﬁll speciﬁed needs, which are based on the appli-

cation. Hence, there is no predeﬁned speciﬁcation of

a gateway. Although there are no ﬁxed design ap-

proaches for gateway design, certain common func-

tions can still be assumed for any specialized com-

munications gateway: routing, protocol conversion,

dataﬂow control, real time constraint checking for

message transmission and message ﬁltering or seg-

mentation. The purpose of this paper is to develop

a universal gateway model, which facilitates the com-

munications between different networks. The design

of the presented approach is similar to the idea of a

time triggered gateway described in (Shaheen et al.,

2007).

As described in (Fahmy, 1995), the gateway

model is based on a shared medium approach, which

uses an internal network to exchange uncommitted

messages between Host and Gateway Core. Received

frames are converted to an uncommitted protocol, af-

ter which the information is handled by the gateway

module. Finally the information is converted to match

the destination protocol. The uncommitted protocol

contains three values: Source Identiﬁer, Destination

Identiﬁer and Dataﬁeld. The routing information of

each message can be identiﬁed by Source Identiﬁer

and Destination Identiﬁer. The data of the received

message is stored in the Dataﬁeld of the uncommit-

ted message. To fulﬁll the ﬂexibility requirement the

gateway model is a composition of two kinds of mod-

ules: protocol related and unrelated modules. Only

uncommitted gateway messages can be processed in-

side the protocol unrelated modules, and the proto-

col related modules process the speciﬁc protocol mes-

sages. In order to extend the gateway model to sup-

port a larger amount of protocols, only the protocol

related modules need to be created, while the proto-

col unrelated modules remain unchanged. This ap-

proach provides enormous reusability, replace ability

and extensibility. It allows an easy generation of a

customized gateway to realize relevant system char-

acteristics.

An important aspect of the gateway functionality

refers to (H¨orner, 2007). A gateway should provide

at least two methods of data exchange - PDU based

and signal based gateway functions. A PDU gate-

way routes the protocol data units (PDUs) unchanged

between two networks. In this case the data carried

on both networks, source and destination, are identi-

cal regarding content and length. It is also possible,

that only signals, which are contained in the received

PDUs from source network, are needed on the other

network. In this case, the gateway does not trans-

fer the entire PDU, but sends the individual signals

to the corresponding destination network. To achieve

this, a single received PDU is disassembled in signals

according to the speciﬁcation of the source network.

Afterwards signals are grouped together congruent to

conﬁguration of the destination network and assem-

bled to PDUs, which are send across the destination

network.

The central unit of the gateway model is the mod-

ule Gateway Core shown in Figure 3. This module

contains protocol unrelated functions, e.g. buffering

of received messages, routing, message segmentation

and disassembling messages into signals. Based on

the speciﬁcation of function blocks with standardized

interfaces a high adaptability of the architecture is

achieved allowing the extension and substitution of

single functions. Therefore it is possible to analyze

the system performance of several realizations differ-

ing in their buffer strategy. In contrast to the gateway

TransmitMessage

TransmitSignal

SplitFrameToSignal

SendMsg

RoutingUnitDelay

Delay

FIFOQueue

CoreControlUnit

CoreSwitch

Init_Gateway

Trigger

FromHost CtrlMsgInput

OverFlow

ToHost

Figure 3: Module Gateway Core.

core, the protocol related gateway functions, such as

protocol conversion, initialization of the communica-

ICINCO 2009 - 6th International Conference on Informatics in Control, Automation and Robotics

232

tion controller, message transmission and message re-

ception, etc. are realized within the respective Host

module. The host connected to the source network

receives a message via the CC and converts it into

an uncommitted message. Afterwards the message is

sent to the gateway core. Inside the gateway core, the

uncommitted message will be processed and routed to

the destination host. There it is converted into the cor-

responding standard. Each host has a distinct identi-

ﬁer. This allows the connection of an unlimited num-

ber of networks to the gateway model.

The example scenario shown in Figure 4 contains

two CAN and two FlexRay networks which are con-

nected by a gateway. The system itself is an ex-

tension of an application presented in (Hedenetz and

Belschner, 1998). Each network contains two or more

nodes. The behavior of the used modules CCs realizes

the connection to CAN and FlexRay. The analysis of

the simulation results showed the correct behavior of

the created model.

Brake1 Brake2

Brake3

Brake4

BBWM1PM1

Cluster 1

PM2BBWM2

Cluster 2

Gateway

Port 1

Port 2

Port 3

Port 4

Cluster 3

CAN F

CAN E

CAN D

CAN C

CAN B

CAN A

Cluster 4

Figure 4: System used as reference for validation.

5 CONCLUSIONS

The modeling strategy and developed common gate-

way model presented in this paper allow the universal

design and analysis of heterogeneous communication

networks. Modularized components in the gateway li-

brary represent available functions of a gateway facil-

ity and allow an easy construction of a wide range of

systems. The basic model concept behind the gateway

model enables the analysis of communication and be-

havior of heterogeneous networked systems and sup-

ports the design process of such systems. In early

stages of the development process the evaluation and

veriﬁcation of system properties can be provided prior

to hardware design.

Up to now there are only few communication pro-

tocol models available. To extend the ability for sys-

tem modeling it is necessary to extend the stock of

models. At present this limits the systems which can

be analyzed by the presented approach to CAN and

FlexRay systems. To gain access to real world exam-

ples from within the automotive application domain

the design of models realizing MOST (Media Ori-

ented Systems Transport) and LIN (Local Intercon-

nect Network) are required. Future work will also

deal with the automated import of gateway routing

information by using e.g. CAN Database and FIBEX

(ASAM, 2007). This can be supplemented by con-

cepts of automated model generation.

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