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[C2X] Summer 2014 Protocols: FlexRay and MOST 1

PROTOCOLS: FLEXRAY AND MOST Part 1: In-‐Car Networking


FlexRay

²  MoGvaGon ª  Drive/Brake/Steer-‐by-‐Wire ª  CAN bus is prone to failures

§  Line topology §  No redundant links

ª  CAN bus is slow ª  Need for short bus lines ⇨ deployment expensive, complicated ª  Non-‐determinism for all but one message class

§  Worst case delay unacceptably high

ª  Early soluGons by OEMs proprietary §  TTCAN, TTP/TTA, Byteflight, ...

ª  FoundaGon of consorGum to develop new bus: FlexRay §  BMW, VW, Daimler, GM, Bosch, NXP, Freescale

ª  First series deployment at end of 2006 (BMW X5)


FlexRay

²  Bus topology ª  Line, Star with bus terminaGon ª  Max. distance per line: 24m ª  OpGonal use of second channel

§  Higher redundancy or(!) higher speed §  Up to 10 MBit/s for single channel, 20 MBit/s for dual channel

ECU ECU

ECU ECU

S

ECU ECU

ECU ECU

S

24m 24m 24m


FlexRay

²  Bit transmission ª  Need synchronized clocks in sender and receiver ª  Thus, need addiGonal bits for synchronizing signal sampling at

receiver (done with each 1⇨0 flank) ª  Don’t use bit stuffing

otherwise: message length becomes non-‐determinisGc (cf. CAN) ª  New concept: frame each transmission, each frame, each Byte

§  Bus idle (1) §  Transmission Start Signal (0)

•  Frame Start Signal (1) »  Byte Start Signal (1) »  Byte Start Signal (0) »  8 Bit Payload (…)

•  Frame End Signal (0)

§  Transmission End Signal (1)


FlexRay

²  Bus access ª  Bus cycle (ca. 1 μs .. 7 μs)

§  StaGc Segment §  Dynamic Segment (opt.) §  Symbol Window (opt.) §  Network Idle Time

ª  Global Cycle Counter keeps track of bus cycles passed

²  StaGc Segment ª  Slots of fixed length (2 .. 1023) ª  One Message per Slot ª  StaGc assignment (of slot and channel) to ECUs (i.e., TDMA)

⇨ bus access is collision free, determinisGc


FlexRay

²  Dynamic Segment ª  Split into minislots (also staGcally assigned to ECUs) ª  Messages (usually) take up more than one minislot ª  Slot counter pauses while message is being transmijed

(thus, slot counters of channels A and B soon desynchronize) ª  Lower priority messages have higher slot number

(thus sent later, or not at all)

²  Example:

Static Segment Dynamic Segment Sym Net Idle (mini)slots Channel A 1 2 3 4 5 6 7 8 9

Channel B 1 2 3 4 5 6 7


FlexRay

²  Message format ª  Control Bits

§  Bit 0: Reserved •  Unused, always 0

§  Bit 1: Payload Preamble Indicator •  In staGc segment:

first 0 .. 12 Byte payload for management informaGon •  In dynamic segment:

first 2 Byte payload contains Message ID (cf. UDP Port)

5 Bit 11 Bit 7 Bit 11 Bit 6 Bit 24 Bit

Control Bits Frame ID Length Header CRC

Cycle Counter Payload CRC


FlexRay

²  Message format ª  Control Bits

§  Bit 2: Null Frame Indicator •  Indicates frame without payload •  Allows sending “no message” also in staGc segment (fixed slot lengths!)

§  Bit 3: Sync Frame Indicator •  Indicates frame may be used for synchronizing clock •  To be sent by 2 .. 15 “reliable” ECUs

§  Bit 4: Startup Frame Indicator •  Used for synchronizaGon during bootstrap •  Sent by cold start node (⇨ later slides)





FlexRay

²  Message format ª  Frame ID

§  IdenGfies message (≜ slot number)

ª  Length §  Length of payload (in 16 Bit words)

ª  Header CRC ª  Cycle Counter

§  Global counter of passed bus cycles ª  Payload

§  0 .. 127 16 Bit words (≜ 0 .. 254 Byte of payload) ª  CRC





FlexRay

²  Time synchronizaGon ª  Need synchronized bit clock + synchronized slot counter ª  Want no dedicated Gme master ⇨ Distributed synchronizaGon ª  Configure (typically) three nodes as “cold start nodes”

ª  Cold start procedure (followed by all cold start nodes): §  Check if bus idle

•  if bus not idle ⇨ abort (cold start already proceeding or unneeded)

§  Transmit wakeup (WUP) pajern •  if collision occurs ⇨ abort •  if no collisions occurred ⇨ this is the leading cold start node

ª  Cold start procedure (leading cold start node): §  Send Collision Avoidance Symbol (CAS) §  Start regular operaGons (cycle counter starts at 0)

•  Set Bits: Startup Frame Indicator ⊕ Sync Frame Indicator


FlexRay

²  Time synchronizaGon ª  Cold start procedure (other cold start nodes)

§  Wait for 4 Frames of leading cold start node §  Start regular operaGons

•  Set Bits: Startup Frame Indicator ⊕ Sync Frame Indicator

ª  Cold start procedure (regular ECUs) §  Wait for 2 Frames of 2 cold start nodes §  Start regular operaGons

*1* WUP WUP CAS 0 1 2 3 4 5 6 7 8 ...

*2* WUP ↯ 4 5 6 7 8 ...

*3* ↯ 4 5 6 7 8 ...

4 6 7 8 ...

5 6 7 8 ...


FlexRay

²  Example configuraGon of Gming ª  Use fixed payload length of 16 Byte

(with header and trailer: 24 Bytes; with FSS, BSS, FES: ca. 250 Bits) ª  10 Mbps data rate ⇨ 25 µs message duraGon ª  Add 5 µs guard to care for propagaGon delay and clock driq ⇨ 35 µs slot length in staGc segment

ª  One macro Gck: 1 µs (can use 1 .. 6 µs) ª  One minislot: 5 macro Gcks: 5 µs ª  Tbit = 100 ns, sample rate of bus = Tbit/8 = 12.5 ns

FlexRay frame with 16 Byte payload

Slot Starts

Slot Ends

Channel Idle

static slot length = Tstatic,slot = 35 macro ticks = 35 µs

Action Point Offset TAP,Offset

frame duration TF ≈ 25 µs


FlexRay

²  Example configuraGon of Gming (contd.) ª  Use 64 disGnct communicaGon cycles ª  CommunicaGon cycle duraGon: 5 ms ª  Use 3 ms for staGc segment ª  Remaining 2 ms used for dynamic segment, symbol window,

network idle Gme

²  Message repeGGon interval fully customizable, e.g.: §  2.5 ms (one slot each at start and end of staGc segment) §  5 ms (one slot each in every communicaGon cycle) §  10 ms (one slot in every second communicaGon cycle) §  …


FlexRay

²  Example configuraGon of Gming (contd.)

0.5ms . . . . . .

10ms

. . .

20ms

10ms

40ms

10ms

20ms

0.5ms . . . . . .

Static Segment

Dynamic Segment

SYM +NIT

Cycle 00

Cycle 01

Cycle 02

Cycle 03

Cycle 04

Cycle 05

Cycle 63

2.5ms Slots

5ms Slots

Cycle Multiplexing Slots

2.5ms Slots

5ms 2ms

1,9ms 3ms

2.5ms

100 µs Every…

Every…


FlexRay

²  Error prevenGon ª  Integrate bus guard ª  Implement separately from communicaGon controller ª  Follows protocol steps in communicaGon controller ª  Can only enable bus driver when allowed to communicate,

or permanently disable in case of errors (babbling idiot problem)

Enable Bus Guard Enable

Application Logic

Comm Controller

Bus Driver

Flex

Ray

Bus


FlexRay

²  Error handling ª  MulGple measures for error detecGon

§  Check cycle counter value §  Check slot counter value §  Check slot Gming §  Check header CRC §  Check CRC

ª  ReacGon to Gming errors §  Do not automaGcally repeat messages (⇨ non-‐determinism) §  Switch to passive state instead

•  Stop transmisng messages •  Keep receiving messages

(might allow re-‐synchronizaGon to bus)

ª  ReacGon to severe, non-‐recoverable errors §  Completely switch off bus driver


FlexRay

²  AUTOSAR TP ª  Transport protocol of FlexRay ª  Upwards compaGble to ISO 15765-‐2 (ISO TP for CAN) ª  Adjusted and extended for FlexRay ª  Difference in addressing

§  In CAN: CAN message ID assigned arbitrarily §  In FlexRay: Frame ID ≜ Slot Number (i.e., not arbitrary) ⇨ cannot use source/desGnaGon addresses as IDs in lower layer

§  Address encoded only (and completely) in TP header

ª  Also: §  New message types

1 .. 2 Byte 1 .. 2 Byte 1 .. 5 Byte Target Address Source Address PCI Payload


FlexRay

²  AUTOSAR TP ª  Frame types: Single Frame Extended / First Frame Extended ª  Larger data length (DL) field allows for longer payload

§  Four kinds of first frames can indicate payloads of up to 4 GiB

PCI Byte 0 PCI Byte 1 PCI Byte 2 PCI Byte 3 PCI Byte 4

Single Frame 0 DL

Single Frame Extended* 5 0 DL

First Frame 1 DL

First Frame Extended* 4 1 DL

“ 4 2 DL

“ 4 3 DL

“ 4 4 DL


FlexRay

²  AUTOSAR TP ª  Extended flow control

§  FS values allow triggering abort of ongoing transmission •  FS=2: Overflow •  FS=5: Cancel, Data Outdated •  FS=6: Cancel, No Buffer •  FS=7: Cancel, Other

§  ST split into two ranges to allow shorter separaGon Gmes •  0x00 .. 0x7F SeparaGon Time in ms •  0xF1 .. 0xF9 SeparaGon Time in μs (new!)

PCI Byte 0 PCI Byte 1 PCI Byte 2 PCI Byte 3 PCI Byte 4 Consecutive Frame 2 SN

Consecutive Frame 2* 6 SN

Flow Control Frame 3 FS BS ST

Acknowledge Frame* 7 FS BS ST ACK SN


FlexRay

²  AUTOSAR TP ª  Extended flow control

§  CAN: Acknowledgement by transmisng dominant bit in ACK field §  FlexRay: New Acknowledge Frame (AF) §  Use aqer single frame or aqer all consecuGve frames (as ACK) or immediately (as NACK)

§  FuncGons idenGcal to Flow Control Frame, but adds ACK and SN nibbles

•  ACK is 1 or 0; SN indicates slot number of first defecGve frame

§  Sender may repeat failed transmissions at earliest convenience (alternately uses CF and CF2 frames)

PCI Byte 0 PCI Byte 1 PCI Byte 2 PCI Byte 3 PCI Byte 4 Consecutive Frame 2 SN

Consecutive Frame 2* 6 SN

Flow Control Frame 3 FS BS ST

Acknowledge Frame* 7 FS BS ST ACK SN


MOST

²  Media Oriented Systems Transport ª  specifies ISO layers 1 through 7 ª  Does not focus on sensor/actor tasks

(e.g., delay, fault tolerance), but on infotainment (e.g., jijer, data rate)

²  History ª  DomesGc Data Bus (D2B, later: DomesGc Digital Bus) developed

by Philips, later standardized as IEC 61030 (sGll in the 90s) ª  Lijle adopGon in vehicles, thus SMSC soon develops a successor ª  1998: MOST CooperaGon standardizes MOST bus

(Harman/Becker, BMW, DaimlerChrysler, SMSC) ª  December 2009: MOST 3.0E1 published ª  Today:

MOST cooperaGon numbers 60 OEMs, 15 vehicle manufacturers


MOST

²  Medium ª  PlasGc OpGc Fiber (POF)

alternaGve (copper) variant specified, but lijle used ª  Data rates specified from 25 (MOST25) to 150 MBit/s (MOST150) ª  Manchester coded bit transmission ª  Dedicated Gming master ECU (slaves adopt bit Gming) ª  Logical bus topology: ring of up to 64 ECUs ª  Physical bus topology can differ

Master ECU

ECU

ECU ECU

POF ECU


MOST

²  Link Layer ª  Synchronous bit stream; all clocks synchronized to Gming master ª  Stream divided into blocks; each block traverses ring exactly once ª  Blocks divided into 16 Frames

§  Frame size: 64 Byte (MOST25) to 384 Byte (MOST150) §  Frame rate staGc but configurable; recommended: 48 kHz (DVD)

ª  Frame divided into §  Header (with boundary descriptor) and Trailer §  Data: Synchronous Channel, Asynchronous Channel, Control Channel

22,67µs Header 1 Byte

Data Field 60 Byte Synchronous Asynchronous

Trailer 1 Byte

Control Data 2 Byte

Boundary Descriptor

1 Frame = 64 Byte


MOST

²  Link Layer ª  Synchronous Channel

§  Use case: audio or video §  TDMA divides frame into streaming channels

⇨ determinisGc

§  Reserved by messages on control channel §  Thus, no addressing required §  Maximum number of streaming channels limited by frame size

Streaming Channel 1 Streaming Channel 2 Streaming Channel 3 unused CD-Audio, Device A DVD-Video, Device B ...


MOST

²  Link Layer ª  Asynchronous Channel

§  Use case: TCP/IP §  Random access with arbitraGon (based on message priority)

⇨ non-‐determinisGc

§  Single message may take more than one frame §  Short addiGonal header contains source/desGnaGon address, length §  Short addiGonal trailer contains CRC §  No acknowledgement, no automaGc repeat on errors

1 Byte 2 Byte 1 Byte 2 Byte 4 Byte Arbitration Target Address Len Source Address ... CRC


MOST

²  Link Layer ª  Control Channel

§  Management and control data §  Random access with arbitraGon (based on message priority) §  Message length 32 Byte

•  MOST25 control channel uses 2 Bytes per frame ⇨ each message takes 16 Frames = 1 Block

§  Message recepGon is acknowledged by recipient §  Failed transmissions are automaGcally repeated

1 Byte 2 Byte 2 Byte 1 Byte 17 Byte 2 Byte 1 Byte

Arbitration Target Address

Source Address Type Data CRC Trailer


MOST

²  Link Layer ª  Control Channel messages

§  Resource AllocaGon, Resource De-‐allocaGon:

•  manage streaming channels in synchronous segment

§  Remote Read, Remote Write

•  accesses registers and configuraGon of ECUs

§  Remote Get Source •  query owner of streaming channels in synchronous segment

§  … •  Other message types are transparently passed to upper layers


MOST

²  Link Layer ª  Addressing

§  16 Bit addresses §  physical address

•  According to relaGve posiGon in ring •  Master gets 0x400 •  First slave gets 0x401 •  etc.

§  logical address •  Assigned by master •  Typically upwards of 0x100 (Master)

§  groupcast •  Typically 0x300 + ID of funcGon block

§  broadcast •  Typically 0x3C8


MOST

²  Ring disrupGon ª  Causes

§  ECU stops working §  PlasGc opGc fiber gets damaged

ª  Symptoms §  Messages either not transmijed to recipient, or not back to sender thus: total failure of bus

ª  Diagnosis §  Ring disrupGon easily detected §  Reason and affected ECUs impossible to determine

ª  Workarounds §  Vendor dependent, proprietary §  oqen: use addiGonal single-‐wire bus for further diagnosis


MOST

²  Higher layers: the Logical Device Model

Source: MOST Specification 3.0E1

NetBlock

Function Block

Function Block

Function Block

Application 1

Application 2

MOST Network Interface Controller

Network Service

Physical Interface

MOST Device


MOST

²  Higher layers: Object oriented MOST Network Services ª  FuncGon block (= class)

§  e.g. audio signal processing (0x21), audio amplifier (0x22), ... §  MulGple classes per device, mulGple devices per class §  Every device implements funcGon block 0x01 (MOST Netw. Services)

ª  Instance §  Uniquely idenGfies single device implemenGng certain funcGon block

ª  Property/Method §  Property (get/set value) §  Method (execute acGon)

ª  OperaGon §  Set/Get/... (Property), Start/Abort/... (Method)

ª  22.00.400.0 (20) ⇨ amplifier number 0: volume set to 20


MOST

²  Higher layers: System boot and restart ª  Master node announces reset of global state

(all devices change status to Not-‐OK and cease operaGons) ª  Master node iniGates system scan

§  IteraGvely polls all physical addresses for present funcGon blocks §  Devices answer with logical address, list of funcGon blocks, and instance numbers

ª  Master can detect ambiguous combinaGons of funcGon blocks and instance numbers ⇨ will then assign new instance numbers

ª  Master keeps table of all device’s operaGon characterisGcs ª  Master reports to all devices: status OK ª  MOST Bus is now operaGonal


MOST

²  Higher layers – MAMAC and DTCP ª  Trend towards all-‐IP in consumer electronics

addressed in MOST by introducing MAMAC (MOST Asynchronous Media Access Control) §  Encapsulates Ethernet and TCP/IP for transmission on MOST bus §  but: not supported by MOST services; needs to be implemented in soqware

ª  Concerns of music/film industry wrt. digital transmission addressed in MOST by introducing DTCP (Digital Transmission Content ProtecGon) §  As known from IEEE 1394 (FireWire) §  BidirecGonal authenGcaGon and key exchange of sender/receiver §  Encrypted data transmission


In-‐Car Ethernet

²  IEEE 802.3 ²  Bob Metcalfe, David R. Boggs ²  1973, Parc CSMA/CD Ethernet

ª  3 Mbit/s, 256 nodes, 1 km coax cable

²  1980-‐ revised to become IEEE Std 802.3 ²  Next big thing?

ª  “AutomoGve. Cars will have three networks. (1) Within the car. (2) From the car up to the Internet. And (3) among cars. IEEE 802 is ramping up for these standards now, I hope.” -‐-‐/u/BobMetcalfe on hjp://redd.it/1x3fiq


In-‐Car Ethernet

²  Why? ª  Old concept:

§  Strictly separated domains §  Each served by specialized bus §  Minimal data interchange

ª  Current trend: §  Advanced Driver Assistance Systems (ADAS) §  Sensor data fusion

•  (in-‐car, between cars) §  Ex: CooperaGve AdapGve Cruise Control (CACC)

ª  Move from domain specific buses ⇨ general-‐purpose bus


Ethernet

²  Physical layers ª  10BASE5 (aka Thicknet, aka IEEE Std 802.3-‐1985)

§  Manchester coded signal, typ. 2 V rise §  10 Mbit/s over 500m coax cable §  Nodes tap into core (“vampire tap”)

ª  10BASE2 §  10 Mbit/s over “almost” 200m coax cable §  BNC connectors, T-‐shaped connectors

²  Medium access: CSMA/CD ª  Carrier sensed ⇨ medium busy ª  Collision ⇨ jam signal, binary exponenGal backoff (up to 16 Gmes)


Ethernet

²  Physical layers ª  1000BASE-‐T

§  1 Gbit/s over 100m §  Cat 5e cable with 8P8C connectors, 4 twisted pairs of wires, mulG-‐level signal (-‐2, -‐1, 0, +1, +2), scrambling, …

§  Medium access §  No longer shared bus, but point to point §  Auto-‐negoGated (Gming) master/slave

ª  100GBASE-‐ER4 §  100 Gbit/s over 40 km §  PlasGc OpGc Fiber (POF)

ª  …


Ethernet

²  Link layer ª  Lightweight frame type ª  OpGonal extensions, e.g., IEEE 802.1Q (idenGfier 0x8100) ª  Directly encapsulates higher layer protocols, e.g., IPv6 (0x86DD) ª  …or IEEE 802.2 Logical Link Control (LLC) frame (idenGfier is len)

ª  Error-‐checked, but only best effort delivery of data

0 7 8 15 Preamble (1010..11) Destination MAC

Source MAC (opt) 802.1Q tag Type/len

Payload (commonly 42-1500 Byte, max 1982 Byte)

Checksum (Idle time)

(in Byte)


In-‐Car Ethernet

²  In-‐car Ethernet? ª  Almost all “in-‐car” qualiGes absent

§  Heavy, bulky cabling §  Huge connectors §  SensiGve to interference §  Needs external power §  No delay/jijer/… guarantees §  No synchronizaGon §  Etc…

ª  But: §  …can be easily extended: §  New physical layers §  Tailored higher-‐layer protocols


In-‐Car Ethernet

²  One-‐Pair Ether-‐Net (OPEN) alliance SIG ª  Founded: BMW, Broadcom, Freescale,

Harman, Hyundai, NXP ª  2014: approx. 150 members ª  100 Mbit/s on single twisted pair, unshielded cable ª  Power over Ethernet (IEEE 802.3at) ª  Manufactured by Broadcom, marketed as BroadR-‐Reach

²  Reduced Twisted Pair Gigabit Ethernet (RTPGE) task force ª  Working on IEEE 802.3bp ª  1 Gbit/s over up to 15m

single twisted pair cable

Source: Rosenberger Hochfrequenztechnik GmbH & Co. KG


In-‐Car Ethernet

²  Upper layers: TSN ª  Many soluGons (e.g., SAE AS6802 “Time Triggered Ethernet”) ª  Current: IEEE 802.1 Time SensiGve Networking (TSN) task group

(aka Audio/Video Bridging AVB task group, up unGl 2012) ª  Promoted by AVnu Alliance SIG (cf. IEEE 802.11 / Wi-‐Fi Alliance)

²  Concept ª  Needs TSN-‐enabled switches / end devices ª  Tight global Gme synchronizaGon ª  Dynamic resource reservaGon on streams through network ª  IEEE 802.1AS… extensions

§  Layer 2 service ª  IEEE 802.1Q… extensions

§  Frame tagging standard


In-‐Car Ethernet

²  IEEE 802.1AS Time Synchronizing Service ª  Subset of IEEE 1588 Precision Time Protocol (PTP) ª  Syncs clock value/frequency of all nodes ª  ElecGon of “master” Gme master (grandmaster clock),

disseminates sync informaGon along spanning tree

²  IEEE 802.1Qat Stream ReservaGon Protocol (SRP) ª  Talker adverGses stream (along with parameters) ª  AdverGsement is disseminated through network ª  Intermediate nodes check, block available resources, update

adverGsement with, e.g., newly computed worst case latency ª  Listeners check (annotated) adverGsement, send registraGon

message back to Talker ª  Intermediate nodes reserve resources, update mulGcast tree


In-‐Car Ethernet

²  IEEE 802.1Qav etc. Traffic Shaping ª  PrioriGze frames according to tags ª  Avoid starvaGon, bursts, … ª  e.g., Token bucket, with many more proposed

²  IEEE 802.1Qbu Frame PreempGon ª  Can cancel ongoing transmissions

(if higher priority frame arrives)

²  IEEE 802.1Qcb Media Redundancy

²  …


Main Takeaways

²  FlexRay ª  MoGvaGon ª  Single or dual channel operaGon ª  Distributed operaGon ª  StaGc and dynamic segment

²  MOST ª  MoGvaGon ª  Topology and implicaGons ª  Centralized operaGon ª  Synchronous and asynchronous channel

²  Ethernet ª  Concept ª  Drawbacks of classic standards ª  New PHY layers ª  New upper layers (TSN)

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