Challenges and approach



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CHALLENGES AND APPROACH

The previous ECU-centric system 

architecture with its point-to-point com-

munication infrastructure is no longer 

an effi cient design approach. Automo-

tive electronic systems are becoming 

truly distributed to achieve increased 

system functionality by tightly coupling 

ECUs. These changes encourage a signi-

fi cantly revised approach to automotive 

system test. This shift in system design 

is refl ected in the evolution of ISO26262 

[1], derived from IEC61508 [2], with its 

focus on functional safety assurance. It 

has a huge impact on automotive test 

platforms, Hardware-in-the-loop(HiL) 

simulation, test platform provider. Audi 

is responding to these challenges by 

radically re-thinking the architecture of 

the HiL test platform and defi ning a 

next generation approach.

The new approach introduces the con-

cept of a HiL-Bus to integrate the functio-

nality of multiple existing HiL sub-sys-

tems and meet the needs of a function-

centric test environment.

FUNCTIONALITY THROUGH 

DISTRIBUTED ECUS

We need to start by describing the shift 

towards function-centric testing from the 

perspective of automotive design. Here 

are a few examples:

 : A simple “air bag computer” fi res the 

air bags at the time of a crash. This ECU 

now becomes an integral element of a 

complex safety sub-system with more 

safety functions. The safety computer 

has to have an automatic crash detec-

tion capability (“Audi pre-sense”) and it 

has to perform fully automated braking 

support, deploy the air bags, tension the 

aU t H o rS

CONSTANTIN BRÜCKNER

is working in the department 

Hardware-in-the-Loop Functional test at 

audi aG in Ingolstadt (Germany).

BETTINA SWYNNERTON

is technical Manager eMea at real-time 

Innovations Inc. in Sunnyvale (USa).

A NEW ARCHITECTURE FOR AUTOMOTIVE 

HARDWARE-IN-THE-LOOP TEST

as automotive electronic system design evolves, so must the HiL testbench and automotive test platforms. the 

fundamental functional design approach has been modular and eCU-centric, but the eCU count has steadily 

increased. the next big shift is to achieve functionality through the integration of multiple eCUs. audi is responding 

to these challenges by radically re-thinking the architecture of the HiL test platform and defi ning a next generation 

approach. the new approach introduces the concept of a HiL-Bus to integrate the functionality of multiple existing 

HiL sub-systems and meet the needs of a modular best-in-class test ecosystem. By using a data orientedapproach 

the complexity of the testbench is reduced making it easier to integrate hardware and software products from 

different vendors. one of the enabling technologies (Connext ddS) is developed by real time Innovations Inc. 

 DEVELOPMENT   Hardware-In-tHe-Loop

4 0

Hardware-in-the-Loop




seat belts, close the windows and roof 

and move seats into an upright position.

 

: Dedicated ECUs for radio, navigation 



or rear seat entertainment are evolving 

into a “main entertainment unit.”

 

: Dedicated ECUs for the reading light, 



interior light and body electronics are 

combined into a “body control 

module” and enriched with new capa-

bilities such as bending light, matrix 

LED head light, camera-based night 

vision and traffic sign detection.

This is a different way of looking at 

vehicle development. It has a fundamen-

tal impact on the way in which the auto-

motive HiL test platform needs to be 

designed. It requires a much more flexi-

ble and scalable test environment that is 

capable of bringing together many diffe-

rent HiL simulation platforms into one 

tightly integrated test platform.

A NEW HiL – DESIGN OBJECTIVE 

The HiL test platforms available from the 

ecosystem of platform suppliers for a wide 

range of automotive sub-system simulati-

ons (such as powertrain, engine manage-

ment, braking and air bag deployment), 

have evolved with the historic require-

ments of the stand-alone function-centric 

ECUs. However, new test requirements of 

the full car HiL simulation and function-

centric test environment need something 

new and different to validate the func-

tions of future cars.

Audi identified that different HiL test 

platforms from different suppliers offer 

differing levels of fidelity with respect  

to their simulation and test capabilities. 

New highly integrated and distributed 

functions need a highly distributed HiL 

ecosystem. Multiple HiL sub-systems  

provided by different suppliers have to be 

tightly coupled to reflect the integrated 

distributed function being tested, 

1

. The 


HiL suppliers may only be providing the 

very best sub-system HiL simulation and 

test capabilities for a fraction of the overall 

function test objective. This would require 

the automotive vendor to compromise the 

full system test fidelity if they source the 

entire platform from one supplier.

Why can’t the automotive company 

select the best HiL-sub-systems and bus 

simulations from across the industry to 

build a new best-in-class function test HiL 

platform? This is the question at the heart 

of Audi’s research into their Modular HiL 

Next Generation mHIL-NG project.

This project is looking beyond test 

platforms; it wants to be able to bring 

the advanced model-based and compu-

ter-aided development tools used in 

actual ECU development into the HiL 

ecosystem.

THE NEW HiL TEST CHALLENGES

Automotive HiL must stay ahead of the 

developments in ECU integration, or at 

least integrate existing ECU development 

processes to keep pace with the rate of 

change in automotive development. 

A next generation automotive HiL 

must be able to deal with:

 

: increasing scale of ECU function 



simulation

 

: increasing complexity of functional 



test requirements

 

: integration of a wide variety of HiL 



modules into function sets

 

: integration of ECU modeling platforms 



for test validation and stimulation

 

: standardised and simplified interface 



for user interaction and control

 

: signal measurement and stimulation 



across different modules.

Perhaps the most significant decision 

that Audi has made is to base the new 

HiL architecture on an open standard 

middleware or bus. The new distributed 

functional test demands, and Audi’s qua-

litative objective (and motto), “Truth in 

Engineering,” can only simultaneously 

be met using open market-accessible 

integration technology.

Audi searched for a software infra-

structure that is real-time capable, 

scalable, field proven to be reliable and 

an open standard. After researching 

available options, Audi identified the 

open standard DDS (Data Distribution 

Service) from the OMG [3] and the con-

formant implementation from Real-Time 

Innovations, which not only met these 

criteria, but was also able to deliver the 

required virtual bus architecture. RTI 

Connext DDS is also demonstrably inte-

grated with leading modeling environ-

ments widely used in software 

development.

A DATA-CENTRIC CORE   

FOR THE HiL-BUS

At the 2013 VDI automotive electronics 

conference in Baden-Baden, the keynote 

[6] emphasised a huge change in the 

automotive software development para-

digm. Specifically, to deal with the  

complexity of future electronic systems 

design, the industry must move to a 

data-centric approach. Audi also noted 

that viewing the integration bus as a 

software databus was the only way  

to bring the best-in-class elements of 

existing proprietary HiL sub-system  

suppliers together with the modeling  

and development tools used in ECU 

development. 

Every HiL testbench or sub-system is 

seen as a module. Each module either 

produces or consumes data, and the 

data is important to the test system. The 

changing state of data represents chan-

ges in system or sub-system state. A 

state change is at the core of being able 

to understand and validate whether a 

suite of ECUs meet a specific functional 

objective. A data-centric system infra-

structure, 

2

, makes state changes visi-



ble on the software bus by updating 

data values, just as a database in an 

enterprise system updates its rows and 

columns. It sustains a real-time view of 

the system-wide state that is immedia-

tely accessible to all sub-systems.

With a data-centric infrastructure in 

place, Audi maintains control of the 

communication infrastructure and can 

decide how to evolve the HiL-Bus to 

meet functional test needs in a simple 

and elegant fashion. This sort of de-cou-

pling capability facilitates the evolution 

of a true plug-and-play automotive test 

platform. The ability to rapidly bring 

together multiple HiL system suppliers 

HiL

-Bus


HiL-Testbench

Vendor A


HiL-Testbench

HiL-Testbench

Vendor B

HiL-Testbench

Vendor C

HiL-Module

Vendor A

HiL-Module

Vendor B

HiL-Module

Vendor C

1

 Audi HiL-Bus – Connecting Multi-Vendor  



HiL Testbenches

41

  03I2014   Volume 9



Hardware-in-the-Loop


into a single functional test environ-

ment has the potential for huge savings 

in set-up time and cost and simultane-

ously supports the best-in-class modular 

selection objective. Of course, it must 

be simple and easy to connect different 

supplier HiL solutions onto the HiL-Bus 

to investigate multiple combinations of 

HiL test platforms to derive the optimal 

functional test platform.

The timing of when a signal change 

in a module occurs is as important to a 

real-time system as the fact that the 

signal change occurred. To this end, the 

DDS standard [4] includes Quality of 

Service (QoS) capabilities that provide 

the ability for applications to specify 

their timing constraints and notify 

applications if these constraints are not 

satisfied. These real-time-capabilities 

are important for measuring signals 

across different HiL-modules.

AN OPEN BUSINESS MODEL

RTI Connext DDS is the implementation 

of the open standard DDS that Audi 

chose to work with. Apart from its vali-

dated real-time performance, its field 

proven robustness and the depth of its 

supporting development tools, RTI Con-

next DDS has one other key value: its 

business model. As Stan Schneider (CEO 

of RTI) stated in his keynote at a FACE 

[5] technical symposium, „RTI is com-

mitted to an open architecture that 

expands thedselection of applications 

and reduces the cost of procurement, 

system integration, upgrades and tech-

nology refresh, while significantly redu-

cing the total lifecycle cost“. To foster 

an ecosystem of HiL simulation sup-

pliers we must maintain a low barrier to 

entry for them to integrate to the Audi 

HiL-Bus. 

Audi provides data definitions to its 

partners for interfacing to the HiL-Bus. 

This lets them be part of a wider func-

tional Automotive HiL test platform, but 

the HiL supplier still needs to connect 

at the software infrastructure level. RTI 

Connext DDS uses an Open Community 

Source (OCS) licensing model. Through 

OCS, any Audi partner can gain access 

to the basic DDS software (including 

source) at no charge and with royalty 

free deployment. The software license 

has none of the copyleft-style restric-

tions typical of many open source soft-

ware products. This makes the integra-

tion of new supplier-modules very easy 

and comfortable. 

THE IMPORTANCE OF DECOUPLING

The other benefit of the real-time-capa-

ble data-centric infrastructure of the 

HiL-Bus is the highly decoupled modular 

development capabilities it supports and 

enforces. It is very important in an open 

architecture such as the HiL-Bus that 

independent, modular development can 

be advanced by contributing developers 

and ecosystem partners. DDS acts as the 

communication and real-time arbiter in 

this software bus system. Its true peer-

to-peer architecture means that it sup-

ports an “any order” boot sequence. DDS 

provides a discovery mechanism that 

treats every modular participant as both 

a sink (subscriber) and a source (publis-

her) of data (and thus state changes) to 

the wider system of systems. By moving 

the communication complexity into the 

bus, Audi massively reduces the integra-

tion problems of connecting different 

sub-systems developed by different part-

ner companies using different methodo-

logies. Now, integrators just have to cha-

racterise their data outputs and source 

requirements and align them with the 

Audi data model. Dr. Jan Effertz of VW 

Research described the benefits of DDS 

in their driver safety systems research 

as, “Think about the data, not how to 

communicate” [6]. Developers just place 

data on the HiL-Bus or take it from the 

HiL-Bus. They do not need to think 

about how to communicate with a speci-

fic end-point which may have attendant 

unique requirements for message 

exchange, 

3

.

Actuator



Display

App


Control

App


Sensor

Sensor


OMG Data Distribution Service (DDS)

Application

Application

Savings


Application logic

Application logic

Data caching and 

state management

Message generation

and parsing

Message generation

and parsing

Data caching and 

state management

Data-centric

middleware

Message-centric

middleware

Network

Message filtering



Message filtering

2

 The OMG DDS databus architecture



3

 Message-centric vs data-centric middleware [5]

DEVELOPMENT  Hardware-In-tHe-Loop

42



TEST AUTOMATION

Automotive vendors such as Audi have 

invested many years in their test automa-

tion environment. Those environments 

include many proprietary setup tools 

that meet the special needs of their 

manufacturing and development organi-

sations, and an incumbent workforce 

skilled with those tools. The introduction 

of the HiL-Bus must embrace existing 

user interfaces to the test platform and 

make it simpler to develop new test 

capabilities. Audi calls the abstraction 

layer their “testbench manager.” Such 

tools can be characterised by their data 

use, and easily interfaced, unchanged, 

onto the HiL-Bus, 

4

, as simply as atta-



ching a plug adaptor for power when tra-

velling abroad.

The testbench manager is a software 

library developed by Audi. It consists of 

two parts: the HiL-Bus interface and the 

test-bench manager itself. This library 

is integrated in every sub-module of a 

testbench, 

5

, and enriched by vendor 



specific glue code for accessing proprie-

tary module functions via the HiL-Bus.

REFERENCES

[1]  ISo 26262, road Vehicles – Functional Safety, 

part 1 – 10, 2011/11

[2]  IeC 61508, Functional Safety of electrical/elect-

ronic/programmable electronic Safety-related Sys-

tems, part 1- 7, 2011/02

[3] object Management Group – data distribution 

Service for real-time Systems v1.2 http://www.omg.

org/cgi-bin/doc?formal/07-01-01

[4]  Kellerwessel, C.: Connectivity im Fahrzeug – 

nutzen und Umsetzung. In: 16

th

 International Kon-



gress „elektronik im Fahrzeug“, Baden-Baden, Ger-

many, 2013/16/10

[5]  Schneider, S.: FaCe Consortium F2F meeting 

June 42013 - http://online.wsj.com/article/pr-Co-

20130530-907778.html 

[6] effertz, J.: Interview wrt ddS 18/04/12 https://

web2.sys-con.com/node/2251954

[7] Schacker, C.: data-Centric Middlewarehttp://

www.rti.com/docs/rtI_data_Centric_Middleware.

pdf


HiL-Module

Glue code

Proprietary software

HiL-Bus


Distributed abstraction layer

(testbench manager) 

including HiL-Bus-interface

4

 Testbench manager as distributed abstraction 



layer

HiL-Modules

HiL-Operations

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Smartphone

Road

simulation



Sensor

simulation

Traffic

simulation



Driver

simulation

Tablet

Test automation



Experimental

software


Control station

Vendor A


Data logger

ECU


Manager

Tester


Tester

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Virtual environment modules

ECU

ECU


ECU

ECU


ECU

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Application module

Glue code

PSM


DDS

Vendor A


Vendor B

Vendor B


Vendor C

5

 Audi HiL-Bus based logical testbench 



architecture

4 3


  03I2014   Volume 9

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