CAN XL - THE NEXT STEP IN CAN EVOLUTION - CURRENT STATUS OF THE CAN XL STANDARDIZATION @ CIA - BOSCH ...
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CAN XL – THE NEXT STEP IN CAN EVOLUTION FEBRUARY 2021 Current status of the CAN XL standardization @ CiA
CAN XL – Next Step in CAN Evolution
Background & Target
Background Bit-rate gap
Cost
Inspired by VW’s demand for a higher bandwidth CAN solution,
officially presented by VW at the ISO/TC 22/SC 31/WG3 plenary
meeting in September 2018 100BASE-T1
Target 10BASE-T1S
Provide a superior 10Mbit/s CAN solution with respect to
► Price (Transceiver, Pins, Cabling, ...)
► Safety
► Security
CAN FD
► Quality of Service
Preserve CAN properties: Arbitration, robustness, long stubs, …
2 10 100 Mbit/s
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CAN XL – Next Step in CAN Evolution
Bit rate ≥12 Mbit/s Priority ID / Message ID Data Field length
Target net bit rate Arbitration Phase Priority ID (bus access priority) Range
10 Mbit/s with large payloads ≤ 1 Mbit/s short (11 bit) enables high net bit rate 1 .. 2048 byte (configurable with byte granularity)
for short payloads
Data Phase: Message ID (identifies message) Enables
1 ... ≥12 Mbit/s – user configured, tradeoff long (32 bit) sent in “Acceptance Field” transparent Ethernet frame tunneling, use
between bit rate & network topology during XL data phase of TCP/IP, SOME/IP, and more
Arbitration Data Trailer
slow: ≤ 1Mbit/s | short: 11 bit ID fast: 1 to ≥12 Mbit/s | long: 1 to 2048 byte slow: ≤ 1Mbit/s
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© Robert Bosch GmbH 2021. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.CAN XL – Next Step in CAN Evolution
Compatibility to CAN FD
CAN FD: Has the res-Bit for future Compatibility of CAN FD and XL enables
protocol extensions
Incremental upgrade path larger acceptance
res-Bit = 0: E/E Architecture design freedom: “mixed FD/XL” or “XL only” networks
CAN FD node expects a CAN FD Frame Mixed CAN FD/XL networks: 2 data bit rates on the same bus (CAN XL is limited to
SIC mode, no Transceiver mode switch allowed)
res-Bit = 1:
► right bandwidth for each bus node | bandwidth/price optimized endpoints
CAN FD node enters
Protocol Exception Mode – a kind of passive wait state
Mixed CAN FD / CAN XL network
CAN FD node Ends
Protocol Exception Mode after the occurrence of 11
consecutive recessive bits CAN FD CAN FD CAN FD
CAN XL CAN FD CAN XL
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MAC Frame Format
Arbitration-Phase Data-Phase Arbitration-Phase
Arbitration Field Control Field Data Field CRC Field ACK Field EOF Field
Priority ID XL ADS SDT SEC DLC SBC PCRC VCID AF Data Bytes FCRC FCP DAS ACK EOF
FD Mode XL Mode FD Mode
Increased Robustness/Safety due to
01 02 03
Fixed Stuff Bits Preface CRC Frame CRC
simplicity & robustness against specific error safeguard DLC (Data Length Code) powerful, safeguards whole frame up to FCRC
types (bit insertion/removal)
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© Robert Bosch GmbH 2021. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.CAN XL – Next Step in CAN Evolution
MAC Frame Format Details1
Arbitration-Phase Data-Phase Arbitration-Phase
Arbitration Field Control Field Data Field CRC Field ACK Field EOF Field
Priority ID XL ADS SDT SEC DLC SBC PCRC VCID AF Data Bytes FCRC FCP DAS ACK EOF
FD Mode XL Mode FD Mode
Dyn. Stuff Bits Fixed Stuff Bits, 1 stuff bit after 10 data bits No Stuff Bits
Priority ID 11-bit ID for bus arbitration, purpose: bus access priority
XL Placeholder in this graphic for several Bits: e.g. Frame Format Switch FD to XL Format
ADS Arbitration Data Sequence Bit Rate Switching from Arbitration to Data Phase
SDT SDU Type (8 bit) indicates the type of the protocol embedded in the data field (comparable to EtherType in Ethernet)
SEC SEC (1 bit) signals, if further Layer 2 functions added headers to the data field (e.g. Security, Segmentation)
DLC Data Length Code (11 bit)
SBC Stuff Bit Count count of dynamic stuff bits in the arbitration field, safeguards against specific error types
PCRC Preface CRC (13 bit) Safeguards the bits up to PCRC
VCID Virtual CAN Network ID (8 bit) allows to separate the CAN Bus into virtual buses (comparable to VLAN ID in Ethernet)
AF Acceptance Field (32 bit) Field for the Addressing, the interpretation of this field depends on SDT
Data 1 to 2048 bytes user data
FCRC Frame CRC (32 bit) Safeguards the whole frame, i.e. the bits up to the FCRC
FCP Format Check Pattern Receiver checks if he is aligned to transmitted bit stream
DAS Data Arbitration Sequence Bit Rate Switching from Data to Arbitration Phase 1 See CiA610-1 for the exact frame format
ACK Positive Acknowledgement, same as in CAN FD
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New Functions on Layer 2
Layer 2 Frame contains 3 new fields
01 02 03
SDT: SDU Type (8 bit) VCID: Virtual CAN Network ID (8 bit) AF: Acceptance Field (32 bit)
Indicates the type of the protocol embedded Allows to separate the CAN network/bus into Depending on SDT it can contain
in the data field virtual networks a) Message ID or
b) Source/Destination address or c) ...
Comparable to EtherType in Ethernet Comparable to VLAN ID in Ethernet
Allows to support both:
CiA611-1 already defines an SDT value for 1) Content based addressing
Ethernet Tunneling 2) Node based addressing
Layer 2 MAC frame format
Arbitration Field Control Field Data Field CRC Field ACK Field EOF Field
Priority ID XL ADS SDT SEC DLC SBC PCRC VCID AF Data Bytes FCRC FCP DAS ACK EOF
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SDU Type (SDT)
Definition
Indicates the type of the protocol embedded in the data field – comparable to EtherType
CiA611-1 in the first version: will specify 4 SDU Types (specification of further values is planed)
8 bit 32 bit 1 ... 2048 byte
... SDT ... AF Data Field ...
Content Based Addressing 0x01 Message ID CAN Data
Dest. Source
Node Addressing 0x02 Address Address CAN Data
IEEE 802.3 (Ethernet) Tunneling 0x03 CAN Frame ID (11 / 29 bit ID) Legacy CAN Frame (FD or Classical)
Truncated
IEEE 802.3 (Ethernet) Tunneling 0x04 Destination MAC Address Ethernet frame, without FCS
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© Robert Bosch GmbH 2021. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.CAN XL – Next Step in CAN Evolution
Transceiver Types usable with CAN XL
TODAY TOMORROW
CAN FD Transceiver CAN FD Transceiver
2 Mbit/s in Data-Phase currently under specification in SIG CAN XL
(realistic with existing bus topologies) @ CiA ≥12 Mbit/s in Date-Phase
CAN SIC Transceiver
(Signal Improvement, former “Ringing Suppression”)
5 Mbit/s in Data-Phase
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Properties of “CAN SIC XL” Transceiver
01 SIC Mode 02 FAST Mode
dominant/recessive (like a CAN SIC transceiver) TX node: push/pull (0/1)
RX node: adjust threshold
The XL Protocol Controller signals the mode switch to the transceiver during ADS & DAS
Layer 2 (MAC)
Arbitration-Phase Data-Phase Arbitration-Phase
Arbitration Field Control Field Data Field CRC Field ACK Field EOF Field
Priority ID XL ADS SDT SEC DLC SBC PCRC VCID AF Data Bytes FCRC FCP DAS ACK EOF
Start signaling End signaling
Layer 1 (Physical Layer)
SIC Mode FAST Mode SIC Mode
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CAN Usability Matrix
Protocol (Data Link Layer) CAN CAN FD CAN XL
8 64 2048
Max. payload
bytes bytes bytes
Transceiver CAN SIC CAN SIC
CAN CAN FD CAN SIC CAN CAN FD CAN SIC
(Physical Layer) XL FAST* XL FAST*
Max. bit rate in real 500 2 5 500 2 5 5 ≥10
OEM applications kbit/s Mbit/s Mbit/s kbit/s Mbit/s Mbit/s Mbit/s Mbit/s
Error Error Error Error Error Error not not
Error Signalling
Flag Flag Flag Flag Flag Flag available available
extra
Topology Dimension large normal large large normal large large
large
* CAN SIC XL Transceiver operated in FAST Mode XL & FD compatible XL and FD NOT compatible
Hint: CAN XL Transceiver operated in SLOW Mode = CAN SIC Transceiver mixed FD/XL network possible pure CAN XL network
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Compatibility
ISLAND 1 ISLAND 2
Full compatibility of FD and XL up to 5-8 Mbit/s CAN XL up to ≥12 Mbit/s
Same device –
Layer 2 CAN FD CAN FD ignores CAN XL CAN XL
Mode configured
(Protocol) Classic CAN CAN XL frames Error Signaling ON by software
Error Signaling OFF
Layer 1 FD SIC XL SIC XL
SIC Same device
(Physical Layer) Classic use without mode switch use with mode switch
Approx. max.
0,5–2 5–8 5–8 12–15
Bit Rate [Mbit/s]
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Comparison – Net Bit Rate over Payload Size
XL Data-Phase
14,00 Equal net bit rate CAN XL has higher
at 405 byte payload net bit rate 15 Mbit/s
12,00
12 Mbit/s
Net Bit-Rate [Mbit/s]
10,00
8,00
8 Mbit/s
6,00
5 Mbit/s
4,00
CAN XL Arbitration-Phase: 600 kbit/s
2,00 XL 15 Mbit/s XL 12,3 Mbit/s
XL 8 Mbit/s XL 5 Mbit/s
10BASE-T1S 10 Mbit/s FlexRay 10 Mbit/s
0,00
0 128 256 384 512 640 768 896 1024 1152 1280 1408 1536 1664 1792 1920 2048
Payload Size [byte]
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Demonstrator
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Key Success Factors
Large payload size
Bit rate ≥12 Mbit/s
01 02 allows tunneling of e.g. Ethernet traffic
just limited by selected PHY technology
(transparent for higher layer protocols)
CAN XL protocol targeted for high speed CAN XL transceivers (10 .. 12, .. ?
All kind of payload types supported – including largest possible
Mbit/s), but also works with CAN FD or CAN SIC transceivers with up to 8 Mbit/s
Ethernet frame, IPv6, …
Incremental upgrade Extreme scalability
03 04
& mixed networks (CAN FD & CAN XL) & wide range of bit rates configurable, any transceiver
Co-existence of “cheap” CAN FD and fast CAN XL nodes in same network (Classic, FD, SIC, SIC XL) usable
Supports complex network topologies AUTOSAR support
05 06
Flexible trade-off between speed and complex networks Concept proposal since early 2020
(e.g. long stubs supported) – will be developed by end of 2021
Price Availability
07 08
expected to be cheaper than 10BASE-T1S CAN XL is technically finalized since Q4/2020,
CiA610-1 specification release planed Q1/2021
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© Robert Bosch GmbH 2021. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.THANK YOU
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