The industry is quickly moving away from a function/signal-oriented architecture towards Service-Oriented Architectures (SOA). To carry-over legacy signal-oriented ECUs during the transition phase, Volvo Cars has developed a layered software (SW) architecture based on the concepts of "device proxys" (i.e., one per legacy ECU), signal real-time database and service interface. This architecture, executing on the central computer on the TSN backbone, provides a clear separation of concerns between its components with a reduced additional complexity. In this presentation, we will review the main challenges faced in the integration of signal-oriented ECUs into SOA, and present the solutions explored at Volvo with a focus on layered SW architecture in the centralized E/E architecture and its 3 core components: o Device Proxies o Signal DataBase o Service Interface We then report on the performances of this architecture in terms of latencies and conclude on the maximum number of signal-oriented frames and legacy ECUs that can be handled. The performance evaluation is conducted by simulation, with sensitivity analysis to identify the performance bottlenecks. The E/E architecture under study is a prototype TSN-based central computing architecture targeted at next-generation models. The main questions that will be discussed throughout the presentation are 1) how to efficiently handle signal to service conversion? 2) The performance and the scalability of the SW architecture proposed and 3) the suitability of SOME/IP as the SOA protocol.

1. Signal-Oriented ECUs in a Centralized Service-Oriented Architecture:
Scalability of the Layered Software Architecture
Automotive Ethernet Congress 2022, Volvo SoA
2022-06-01
Hoai Hoang BENGTSSON & Martin HILLER
Volvo Cars Sweden
Jörn MIGGE
RealTime-at-Work (RTaW)
Nicolas NAVET
Uni. Luxembourg & Cognifyer

2. Agenda
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Introduction of SOA architecture –
Challenges
Service interface communication model
Modelling of the system
Performance evaluation
Conclusion
2

3. Introduction of SOA in next
generation architecture
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA 3

4. Centralized E/E Architecture with Ethernet Backbone
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Ethernet
CAN/CAN FD
Lin
Sensors
and
actuators
VCU
IHU
VIU Right
ADPM
VIU Left
Low Power
Controller
ECU
VIU Front
An ECU in the Mechatronic Rim is highly specialised for
controlling its specific device. For example: engine,
transmission, brakes, steering, doors, windows, seats, ...
The VCU coordinates fundamental capabilities in the Mechatronic Rim
to provide vehicle level behavior. For example: vehicle dynamics,
propulsion control, climate control, exterior lighting, interior lighting, ...
A VIU provides a translation from the specific
network interfaces of the nodes in the Mechatronic
Rim to the Core Network. Think ”Gateway”...
VCU: Vehicle Computation Unit
VIU: Vehicle Integration Unit
ADMP: Autonomous Driving Primary Module
IHU: Infotainment Head Unit
4

5. SW Layering Architecture
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
ECU
ECU
ECU
Functional interface: Accessing the (payload) functionality provided by a device.
Device: One or more ECUs, sensor or actuator in the Mechatronic Rim which are connected to the Core System as one unit.
ECU
Sensor /
Actuator
ECU
VCU
VIU
Administrative interface: Accessing diagnostics, software download, network management, and power management.
CAN
LIN
Ethernet
Integration Layer
Integration Interface
Frames
Application Layer
Signals
Service
5

6. VCU
VIU
Device proxy
Devices and proxies and services, Oh my...
Automotive Ethernet Congress 2022, Volvo SoA
Service
Functionality
Serializer/
Deserializer
Packing/Unpacking
Device
V1 V2
Device PDU D1 D2
UDP packet Device PDU D1 D2
Device frame D1 D2
v1 v2
D1 D2
UDP packet
V3 V4
D3 D4
v3 v4
Device PDU D3 D4
Device PDU D3 D4
Device frame D3 D4
D3 D4
Service
Functionality
Serializer/
Deserializer
Service
Functionality
Serializer/
Deserializer
Service
Software
Download
Serializer/
Deserializer
Service
Network Mgmt
Serializer/
Deserializer
Service
Diagnostics
Serializer/
Deserializer
Function Foo Function Bar
Core System values
Device-level data items
Device-level PDUs
(grouping of device-level
data items into device-
defined groups)
UDP packet containing
device-level PDUs
Device-specific frames
containing device-level
data items
Device-level data items
Device-level values
D1 D2
2022-06-01 6

7. Layering Architecture Concept - Challenges
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Device
Proxy
Device Abstraction Layer (DAL)
Service Service Service
Service
App App
App
Device Device Device
Device
Proxy
Device
Proxy
VCU
How to efficiently transform signals to services? What
are suitable services that a device can provide?
What communication model is suitable for our
architecture choice?
How the design choices affect the system performance?
7

8. Service interface
communication model
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Timing chains from sensor to actuator
comprise several successive
“segments” : data transmission and
functions execution
8

9. Where do end-to-end delays come from ?
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
1. Delays come from processors and network loads
→ f (frequencies, transmission and execution times)
2. Burstiness of the load
3. Waiting times between successive tasks and
messages of a timing chain → our focus
Periodic activations reduce loads!
✓ Several signals into same frame
✓ Periodic tasks and “Publisher-
Subscribers” services → execution
rate under control
Event-Triggered (ET) activations reduce latencies!
✓ No waiting times between segments of a
timing chain
✓ Apps call services whenever needed and get
responses asap (ODS: “On-Demand Service” next)
9

10. Choice of activation model at several levels
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
App App App App
HAL HAL
DP1
HAL
DPn
DPm
DP2
SDB
VIU
ECU ECU ECU
VCU
Publisher-Subscriber model (subscribers are
updated e.g. periodically by server) or Client-
Server model (ODS) ?
CAN / T1S
ETH Periodic (“snapshots”) or ET transmission
when CAN frame arrives at VIU ?
Periodic or ET transmission on signal’s
update?
Device Proxy executed periodically or
triggered by ETH packet ?
Service Interface
Updating signal database
Forwarding on ETH
Transmission on CAN
10

11. ✓ Service level: publisher-
subscriber model (“PubSub”)
with periodic events
✓ Task execution + CAN and
ETH frames are periodic
Design options compared next
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Fully periodic
model
Fully event-
triggered model
Mixed
model
✓ Service level: ODS
✓ CAN frame arriving at a VIU
triggers ETH packet
✓ Signal production triggers
CAN frame
✓ Periodic model for non-
time-critical timing chains
✓ Event-triggered model for
time-critical timing chains
Metric for performance
evaluation : max # of
timing chains supported
Simplifications:
− Safety constraints are not discussed
− PDUs are kept out of the picture as far as possible
11

12. System Model & Performance
evaluation
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA 12

13. System Model :
network
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
3 Zone Controllers
45 ECUs on 9 CAN FD / T1S buses
Links
Speed
ETH: 1Gbps
CAN FD: 2Mbps or
T1S: 10Mbps
Sampling
Period
10ms and 50ms
Timing
Chains
End-to-end
deadlines set to 4x
(25%) or 10x
sampling period
Central Computer with 2 cores for
Apps, 1 for Device Proxy and 1
for Service
[RTaW-Pegase screenshot]
✓ Modelling and simulation with
RTaW-Pegase / SDV
13

14. System model : flows of data between functions
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
ECU D. proxy Service Apps
- Excerpt of the
functional architecture
with a timing chain
highlighted
- Apps are subscribed
to several services and
thus participate in
several timing chains
Executable
Data exchange
Segment of
the timing chain
selected
[RTaW-Pegase
/
SDV
screenshot]
14

15. Step Activation Mechanism Max. Waiting Times
Sensor Task Periodic tasks none
CAN Periodic frames frame period
Ethernet Buffered PDUs buffering timeout
Device Proxy Periodic task period
Service Service event (PubSub) period
Application Periodic tasks period
Service Service method call (ODS) none
Device Proxy Periodic tasks period
Ethernet Buffered PDUs buffering timeout
CAN PDU triggers CAN frame none
Actuator Task Periodic tasks period
Breakdown of an end-to-end delay: periodic + PubSub service
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Sensor Task Application Actuator Task
Lots of waiting times
between successive
segments !
15

16. Breakdown of an End-to-end Delay: periodic + PubSub service
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
End-to-End delays
Delays of a timing chain’s segments
Periodic activations may be a solution only if the
end-to-end latency constraints are several/many
times larger than the sampling periods
[RTaW-Pegase screenshots]
4x or 10x
sampling period
16

17. Step Activation Mechanism Max. Waiting Times Detrimental impact of triggering
Sensor Task Periodic tasks none
CAN Signals trigger CAN frame none higher bus and CPU loads
Ethernet CAN frame trigger ETH frames none higher links and CPU loads
DP Periodic tasks period
Service Service Method call (ODS) period higher load and larger response times
App Periodic tasks none
Service Service Method call none
DP Periodic tasks period
Ethernet PDUs trigger frames none higher links loads
CAN PDU triggers CAN frame none higher bus loads
Actuator
Task
Periodic tasks period
Event Triggered (ET) activation + ODS for critical chains
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Improvements in terms of waiting times
17

18. Periodic + PubSub versus ET + ODS
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
Waiting times disappear with
triggered activations and on-
demand service requests …
at the expense of CPU and
network load
Periodic Triggered
Periodic
Triggered
[RTaW-Pegase screenshots]
18

19. Mixed model is the best option in our case-study
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
- Periodic + PubSub for non-critical chains
(75%, D=10x sampling period)
- ET + ODS for critical chains
(25%, D=4x sampling period)
ET + ODS for all timing chains
# of executables
Each executable involved in 6.5 timing chains on avg
100 100
90
80
48
32
8
0 0 0 0 0 0 0
100 100 100 100
98
94
78
64
58
46
36
22
2
0
50 60 70 80 90 100 110 120 130 140 150 160 170 180
Probability to meet timing
& load constraints when
the # of executables
increases (CAN FD setup)
− Fully periodic model not shown here
as unable to meet timing constraints
− Load, not timing, is the limiting factor
for ET+ODS model
− T1S outperforms CAN FD here but
dependent on setup and parameters
19

20. Takeaways
2022-06-01 Automotive Ethernet Congress 2022, Volvo SoA
ET activation creates coupling
between segments as
jitters/bursts are propagated →
unwanted coupling between sub-
networks, between network and
SW development!
Presented technical solutions explored
by Volvo to integrate signal-based
ECUs in a zone-based SOA
Choice of activation patterns
is key to meeting load and
timing requirements: mix of
both periodic and ET offers
best solution → automation
through DSE algorithms
Local jitter-reduction shaping
strategies may allow to
preserve independence
Time between
forwarding CAN frames
with/wo jitter reduction
(Davis & Navet, 2012) 20

21. Thank you for your attention!