At91sam7 - Can

CAN

04/09/23 1

SAM7

Controller Area Network

CAN

04/09/23 2

CAN Agenda

What is CAN ? Why CAN ? CAN Protocol CAN Higher Layer Protocols CAN Applications AT91 CAN Microcontrollers – Roadmap

CAN

04/09/23 3

What is CAN ? Controller Area Network

Invented by Robert Bosch GmbH in 1980 for automotive applications

Asynchronous Serial Bus Simple 2-wire differential bus Absence of node addressing

• Message identifier specifies contents and priority• Lowest message identifier has highest priority

Non-destructive arbitration system by CSMA with collision detection

Multi-master / Broadcasting concept Sophisticated error detection & handling system

CAN

04/09/23 4

What is CAN ? The CAN is an ISO standard (ISO 11898) for serial communication Today CAN has gained widespread use:

Industrial Automation Automotive, …etc.

The CAN standard includes: Physical layer Data-link layer

• Some message types• Arbitration rules for bus access• Methods for fault detection and fault confinement

CAN

04/09/23 5

Why CAN ? Mature Standard

CAN protocol more than 16 years Numerous CAN products and tools on the market

Hardware implementation of the protocol Combination of error handling and fault confinement with high

transmission speed (up to 1Mb/s) Simple Transmission Medium

Twisted pair of wires is the standard, but also just one wire will work

Other links works, too: Opto - or radio links Excellent Error Handling

CRC error detection mechanism Fault Confinement

Built-in feature to prevent faulty node to block system Most used protocol in industrial and automotive world

CAN

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CAN Protocol

Protocol -

CAN

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ISO-OSI Reference Model

Protocol -

7. Application Layer

5. Session Layer

6. Presentation Layer

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical LayerCAN Protocol

HLPs: CANopen, DeviceNet, OSEK/VDX

Partially Implemented by High Layer Protocol (HLP)

CA

N L

ayer

s

CAN

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ISO-OSI Reference Model (2)

Protocol -

CAN Controller

CAN Transceiver

CAN

04/09/23 9

CAN Bus Logic

Protocol -

Node 1 Node 2 Node 3 Bus

D D D D

D D r D

D r D D

D r r D

r D D D

r D r D

r r D D

r r r r

‘1’ Recessive (r)

‘0’ Dominant (D)

Two logic states on the CAN bus

Bus in dominant state

Bus in recessive stateor idle

Wired-AND Function

CAN

04/09/23 10

Typical CAN Node

Protocol -

µController CAN Controller

CAN Transceiver

CA

N B

usCAN_H

CAN_L

TXD

RXD

CAN Bus is a simple 2-wire differential serial bus

CAN Bus is terminated on each side by a 120 Ohm resistor

CAN

04/09/23 11

CAN Bit Coding & Bit Stuffing

Protocol -

Bit Coding : NRZ (Non-Return-To-Zero code) does not ensure enough edges for synchronization

Stuff Bits are inserted after 5 consecutive bits of the same level Stuff Bits have the inverse level of the previous bit. No deterministic encoding, frame length depends on transmitted data

Number of consecutive bitswith the same polarity

CAN

04/09/23 12

CAN Bus Access and Arbitration:CSMA/CD and AMP

Protocol -

CSMA/CD: Carrier Sense Multiple Access / Collision Detection AMP: Arbitration by Message Priority

CAN

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CAN Bus Synchronization

Protocol -

Hard synchronization at Start Of Frame bit

Re-Synchronization on each Recessive to Dominant bit

CAN

04/09/23 14

CAN Bit Construction

Protocol -

CAN Bit Period Four Time Segments Each Time Segment represents a number of Time Quanta (TQ) 1 Time Quantum 1 period of CAN Controller Clock

1 Bit Time 8 to 25 Time Quanta

SYNC_SEG: synchronize the different nodes PROP_SEG: compensate for signal delays across the network PHASE_SEG1 & 2: compensate for edge phase errors

CAN

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Relation between Baud Rate and Bus Length

Protocol -

CAN

04/09/23 16

Frame Formats

Protocol -

SOF: Start Of Frame CRC: Cyclic Redundancy Code ACK: Acknowledge EOF: End of Frame IFS: Inter Frame Space

CAN

04/09/23 17

Frame Formats (2)

Protocol -

CAN V2.0A Standard Frame: Identifier is 11 bits long

CAN V2.0B Extended Frame: Identifier is 29 bits long

Our CANs supports CAN V2.0A & CAN V2.0B Specification

ID: Identifier IDE: Identifier Extension RTR: Remote Transmission Request

SRR: Substitute Remote Request RB0/1: Reserved bits DLC: Data Length Code

CAN

04/09/23 18

Frame Formats (3)

Protocol -

Four different frame formats:

Data Frame has priority on Remote Frame

Remote Frame : RTR Recessive ‘1’ and No Data Field

Data Frame : RTR Dominant ‘0’

CAN

04/09/23 19

Frame Formats (4)

Protocol -

Error Frame: sent after a violation frame format

Overload Frame: prevents data overflow from a slower CAN

Overload Frames are not really used

CAN

04/09/23 20

Fault Confinement

Protocol -

TEC and REC counters allows to prevent from faulty nodes

CAN Node Error States: Error Active: Normal state, node can send all frames (error frames

included) Error passive: Node can send all frames excluding error frames Bus off: Node is isolated from bus

Internal Counters: TEC & REC TEC: Transmit Error Counter REC: Receive Error Counter

CAN

04/09/23 21

Error Detection Analysis

Protocol -

One undetected error every 1000 years !!!

Error statistics depend on the entire environment Total number of nodes Physical layout EMI disturbance

Automotive example 2000 hours/year Baud rate: 500 kbps 25% bus load

CAN

04/09/23 22

CAN High Layer Protocols

HLP -

CAN

04/09/23 23

HLP Definition

HLP -

One undetected error every 1000 years !!!

CAN protocol defines only the physical and a low data link layer ! The HLP defines:

Start-up behavior Definition of message identifiers for the different nodes Flow control Transportation of messages > 8bytes Definition of contents of Data Frames Status reporting in the system

CAN

04/09/23 24

CANopen

HLP -

CiA (CAN in Automation)

Features CANopen is a subset from CAL (CAN Application Layer) developed by CiA Auto configuration the network Easy access to all device parameters Device synchronization Cyclic and event-driven data transfer Synchronous reading or setting of inputs, outputs or parameters

Applications Machine Automation

Advantages Accommodating the integration of very small sensors and actuators Open and vendor independent Supports inter-operability of different devices High speed real-time capability

CAN

04/09/23 25

DeviceNet

HLP -

CANopen (Europe) – DeviceNet (USA)

Features Created by Allen-Bradley (Rockwell Automation nowadays), now

presented by the users group ODVA (Open DeviceNet Vendor Association)

Power and signal on the same network cable Bus addressing by: Peer-to-Peer with multi-cast & Multi-Master & Master-

Slave Supports only standard CAN


Advantages Low cost communication link and vendor independent Removal and replacement of devices from the network under power

CAN

04/09/23 26

CAN Kingdom

HLP -

CAN Kingdom is more than a HLP (Meta Protocol): Introduced by KVASER, Sweden A ‘King’ (system designer) takes the full responsibility of the system The King is represented by the Capital (supervising node)s CAN Kingdom provides simple unique identification of system nodes


Advantages Designed for safety critical applications Real time performance Scalability Integration of DeviceNet modules in CAN Kingdom possible

CAN

04/09/23 27

SAE J1939

HLP -

Features Developed by Society of Automotive Engineers heavy trucks and bus

division (SAE) Use of the 29 identifiers Support of real-time close loop control

Applications Light to heavy trucks Agriculture equipment e.g. tractors, harvester etc… Engines for public work

CAN

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X-by-wire systems &Time-triggered protocols

HLP -

Predictable new protocols Applications

Automotive, aircraft…

TTCAN: Time Triggered CAN: Robert Bosch GmbH, CiA.

FLexRay: General Motors, DaimlerChrysler, BMW, Motorola, Philips

Semiconductors and Bosch Automotive Group. TTP: Time Triggered Protocol:

PSA Peugeot Citroen, Audi,Volkswagen, Honeywell and Delphi Automotive Systems.

FlexRay is becoming the reference

CAN

04/09/23 29

OSEK/VDX

HLP -

Usually called OSEK

Initiative of: BMW, Bosch, DaimlerChrysler, Opel, Siemens,VW & IIIT of the

University of Karlsruhe / PSA and Renault Goal: Portability and re-usability of the application software

OSEK/VDX includes: Communication (Data exchange within and between Control Units) Network Management (Configuration determination and monitoring) Operating System (Real-time executive for ECU software)

Applications Automotive Advantages: Saving in costs and development time

CAN

04/09/23 30

CAN Applications

Applications -

CAN

04/09/23 31

CAN: a Large Field of Applications

Applications -

Building Automation: Heating control, Air Conditioning, Security, Access & Light

Control… Domestic & Food distribution appliances

Washing machines, dishes cleaner, self-service bottle distributors…

Automotive & Transportation Dash Board, Power train & Car Body Train, bus and truck equipment…

Robotic Production Automation:

Control & link of production machines… Medical Agriculture

Harvester, seeding, sowing machines, tractor control...

CAN

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AT91SAM7 CAN Embedded ControllersA1 - A2 - A3 - X

AT91SAM7 -

CAN

04/09/23 33

CAN Controllers Types

3 types of CAN controllers exist: CAN Controllers 2.0 Part A: standard frames CAN Controllers 2.0 Part B Passive or ‘extended frames passive’ CAN Controllers 2.0 Part B Active or ‘extended frames active’

CAN Implementations: 2 main implementations strategy BasicCAN: cheaper CAN Controller

• 1 or 2 Rx buffers (FIFO) and 1 Tx buffer• Minimal Filtering

FullCAN: high performance CAN Controllers• Set of buffers called Mailboxes• Dedicated Mailbox Filtering

Our CANs: 2.0A/2.0B (Active) & FullCAN

AT91SAM7 -

CAN

04/09/23 34

CAN Controllers Features Two different CAN implementations for the AT91SAM7 family:

CAN embedded in SAM7A1 & SAM7A2 (Europe Technologies CAN) CAN embedded in SAM7A3 & SAM7X (ATMEL Rousset CAN)

AT91SAM7A1: 1 CAN Controller 2.0A and 2.0B FullCAN with 16 Mailboxes

AT91SAM7A2: 4 CAN Controllers 2.0A and 2.0B FullCAN

• 1 with 32 Mailboxes, 3 with 16 Mailboxes AT91SAM7A3:

2 CAN Controllers 2.0A and 2.0B FullCAN with 16 Mailboxes AT91SAM7X:

1 CAN Controller 2.0A and 2.0B FullCAN with 8 Mailboxes

AT91SAM7 -

SAM7A1-A2 Specific / SAM7A3-X Specific

CAN

04/09/23 35

CAN Controllers Features (2) Fully Compliant with CAN 2.0 Part A and 2.0 Part B High Speed CAN: Bit Rates up to 1Mbit/s Data, Remote, Error and Overload Frame Handling Mailboxes with the Following Properties:

Standard or Extended ID Programmable for Each Message Mailbox Configurable in Receive (with Overwrite or Not) or Transmit Modes Producer & Consumer Mailbox Feature Independent 29-bit Identifier and Mask Defined for Each Mailbox Uses a 16-bit / 32-bit Timestamp on Receive and Transmit Messages Hardware Concatenation of ID Masked Bitfields To Speed Up Family ID Processing

Global 16-bit / 32-bit Internal Timer for Time stamping Priority Management between Transmission Mailboxes:

Mailbox number prioritization Message ID prioritization

Autobaud Mode Automatic retransmission of corrupted messages Low Power Mode and Programmable Wake-up

SAM7A1-A2 Specific / SAM7A3-X Specific

AT91SAM7 -

CAN

04/09/23 36

AT91SAM7A3 – AT91SAM7XCAN Controller

SAM7A3 / SAM7X -

CAN

04/09/23 37

CAN on SAM7X-EK & SAM7A3-EK Boards

PMC has to be programmed 1st for CAN to work: Clock Enabling- Set the PMC_PCER (Peripheral Clock Enable Register).

PIO CAN_TX and CAN_RX have to be configured in peripherals. CAN Transceiver must be enabled through a PIO configured in Output. CAN Internal Timer is 16-bit long. 8 Mailboxes for SAM7X 16 Mailboxes for SAM7A3

SAM7A3 / SAM7X -

CAN

04/09/23 38

CAN Controller Structure

SAM7A3 / SAM7X -

CAN

04/09/23 39

CAN Initialization

SAM7A3 / SAM7X -

CANEN = 1: Enable CAN Controller Wait for bus synchronization (11 consecutive

recessive bits are scanned) WAKEUP flag is set

Status Registers

Error Flags

Mode Register

CANEN 0 ABM 2

ABM = 1: Enable Autobaud Mode Error counters are disabled Transmission is disabled

CAN

04/09/23 40

CAN Bit Timing Configuration

SAM7A3 / SAM7X -

Baudrate Register

BRP 16

Time Quantum = (BRP + 1) / MCK

TBIT =TSYNC + TPRS + TPHS1 + TPHS2

Sample Point: point in time at which the bus level is read as the value of that respective bit.

1 Time Quantum 1 period of CAN Controller Clock

CAN

04/09/23 41

CAN Bit Timing Configuration (2)

SAM7A3 / SAM7X -

Nominal Bit Time: 8 to 25 TQ long. Information Processing Time (IPT): time required to determine the bit level of a

sampled bit.

SYNC_SEG is 1 TQ long.

PROP_SEG: 1 to 8 TQ

PHASE_SEG1: 1 to 8 TQ

PHASE_SEG2 = Max(IPT, PHASE_SEG1)

SJW = Min(PHASE_SEG1, 4TQ)

IPT is 2 TQ for ATMEL CANs

Baudrate Register

SJW 12 PROPAG 8PHASE1 4 PHASE2 0

TPRS =TCSC * (PROPAG+1)

TPHS1 =TCSC * (PHASE1+1)

TPHS2 =TCSC * (PHASE2+1)

TSJW =TCSC * (SJW+1)

CAN

04/09/23 42

Low Power Mode

SAM7A3 / SAM7X -

Low Power Mode: Send or receive messages is disabled (Mailboxes inactive) Enter Low Power Mode:

Set LPM flag All pending transmit messages are sent before Wait for SLEEP signal raising Internal Counter (CAN_TIM) is reset and stuck to 0x0000. The user can disable CAN Clock (PMC)

Exit Low Power Mode: Enable CAN Clock (PMC) Clear LPM flag Wait for bus synchronization WAKEUP signal raising All pending transmit messages are sent before Internal Counter is reset and stuck to 0

Mode Register

LPM 1

Status Register

SLEEP 20 WAKEUP 21

CAN

04/09/23 43

Time Management Unit

SAM7A3 / SAM7X -

Time Management Unit can operate in two modes: Time Stamping Mode (TTM = 0): the value of the internal timer (CAN_TIM)

is captured in the CAN Timestamp register (CAN_TIMESTP) at each:• start of frame (TEOF = 0)• end of frame (TEOF = 1)

Time Triggered Mode (TTM = 1): a mailbox transfer operation is processed when the internal counter reaches the mailbox trigger value (MTIMEMARK field in corresponding mailbox CAN_MMR).

Mode Register

TEOF 4TTM 5 TSTP 23

Status Register

TSTP = 1: A start or an end of frame has been detected

MTIMEMARK 0

Message Mode Register

The CAN controller offers optimized features useful to support the Time-Triggered protocols.

CAN

04/09/23 44

Time Management Unit (2)

SAM7A3 / SAM7X -

CAN_TIM register: Free-running 16-bit timer TIMRST = 1: Allows to clear the counter TIMFRZ = 1: Allows to freeze the counter TOVF = 1: A timer overflow is detected

Transfer Cmd Reg

TIMRST 31 TOVF 22

Status Register Mode Register

TIMFRZ 6

CAN_TIMESTP register: copy of the CAN_TIM after a successful transfer

CAN

04/09/23 45

Data, Remote, Error & Overload Frames Handling

SAM7A3 / SAM7X -

Data & Remote Frames can be sent/received thanks to the different mailboxes: A successful transfer raises the Mailbox Ready flag (MRDY) in the mailbox

status register. When a transmit mailbox looses bus arbitration, the transfer request remains

pending. Disable Repeat DRPT = 1:

• Transfer request is aborted if the transmit mailbox looses bus arbitration.• Mailbox Abort flag (MABT) in the mailbox status register raises.

Error Frames are automatically handled by the macro.

Overload Frames can be generated by setting OVL flag in the Mode Register: OVL = 1: an overload is generated after each successful reception.

Mailbox Status Register

MABT 22

Mode Register

OVL 3 DRPT 7MRDY 23

CAN

04/09/23 46

Mailbox Organisation

SAM7A3 / SAM7X -

Eight 32-bit registers by mailbox

Mailbox x Mode Register Mailbox x Acceptance Mask Register Mailbox x ID Register Mailbox x Family ID Register Mailbox x Status Register Mailbox x Data Low Register Mailbox x Data High Register Mailbox x Control Register

Mailbox Channel Buffer

CAN_MAMxCAN_MAMx

CAN_MMRxCAN_MMRx

CAN_MIDxCAN_MIDx

CAN_MFIDxCAN_MFIDx

CAN_MDLxCAN_MDLx

CAN_MSRxCAN_MSRx

CAN_MDHxCAN_MDHx

CAN_MCRxCAN_MCRx

Mailbox x

CAN

04/09/23 47

Message Acceptance Procedure

SAM7A3 / SAM7X -

CAN_MIDx: defines the message ID MIDE = 0: standard message MIDE = 1: standard or extended message

CAN_MAMx: defines the mask ID value Allows a mailbox to receive different

messages ID.

CAN_MFIDx: concatenation of ID & mask ID Speed up message ID decoding

Mailbox ID & Acceptance Mask Register

MIDE 29

CAN

04/09/23 48

Push / Pull Model

SAM7A3 / SAM7X -

Push Model: Classical Tx Rx Producer Tx Mailbox Consumer Rx Mailbox

Pull Model: Producer Producer Mailbox Consumer Consumer Mailbox Consumer transmit a remote frame

to the Producer. Producer transmit the answer to the

Consumer.

Pull Model: With Tx Rx mailboxes: 1 Tx+ 1 Rx Mailbox for each node 4 Mailboxes

With Consumer Producer mailboxes: 2 Mailboxes only !

CAN

04/09/23 49

Mailbox Object Type

SAM7A3 / SAM7X -

Five programmable type of mailboxes (MOT field in CAN_MMRx)

Reception Mailbox Types:

Receive mailbox: The first message received is stored in mailbox data registers. Other messages are ignored by this mailbox.

Receive with Overwrite mailbox: The first message received is stored in mailbox data registers. The next message overwrites the previous one.

Consumer mailbox (Enhanced Reception Mailbox): Sends a remote frame to a producer mailbox. Waits automatically for a data frame with the same ID from a producer mailbox.

Mailbox Mode Register

MOT 24

CAN

04/09/23 50

Mailbox Object Type (2)

SAM7A3 / SAM7X -

Transmission Mailbox Types:

Transmit mailbox: Sends either a remote frame or a data frame.

Producer mailbox (Enhanced Transmit Mailbox): Waits for a remote frame from a consumer mailbox. Once the remote frame received, sends automatically a data frame with the same

ID to the consumer mailbox.


MOT 24

CAN

04/09/23 51

Mailbox Priority

SAM7A3 / SAM7X -

Reception Modes: In this modes, the mailbox with the lowest number is serviced first.

Transmission Modes: Mailbox with the highest priority PRIOR lowest value. When several mailboxes try to transmit a message at the same time, the mailbox with

the highest priority is services first. If at least two mailboxes have the same priority (same PRIOR value), the mailbox with

the lowest number is serviced first.


PRIOR 16

CAN

04/09/23 52

Transmit Mailbox Handling

SAM7A3 / SAM7X -


MRDY 23

Size of the message is defined in the Mailbox Data Length Code field (MDLC) Mailbox Transfer Command Request (MTCR = 1):

Allows transmission of the current message. Message can be aborted (MACR =1). Mailbox Remote Transmission Request (MRTR = 1):

Allows to send a remote frame (MDLC value is ignored).

Mailbox Control Register

MACR 22MTCR 23 MDLC 16 MRTR 20

CAN

04/09/23 53

Receive Mailbox Handling

SAM7A3 / SAM7X -

Mailbox Transfer Command MTCR = 1: Allows reception of the next message.

When MRDY flag is set, mailbox data registers content is available. MMI flag is set a message has been lost by the mailbox


MTCR 23


MMI 24MRDY 23

CAN

04/09/23 54

Receive with Overwrite Mailbox Handling

SAM7A3 / SAM7X -

Mailbox Transfer Command MTCR = 1: Allows to reset MRDY flag

MMI flag is set a new message has overwritten a previous one.


MTCR 23


MMI 24MRDY 23

CAN

04/09/23 55

Chaining Receive Mailboxes

SAM7A3 / SAM7X -

Allows to receive buffer split into several messages with the same ID buffer size > 8 bytes.

CAN

04/09/23 56

Producer Mailbox Handling

SAM7A3 / SAM7X -

Mailbox Transfer Command MTCR = 1: Allows to wait for a remote frame reception

Data is automatically sent after the reception of a remote frame MRDY remains at 0 as long as the message has not been transmitted or aborted

(MACR =1).


MACR 22


MMI 24MRDY 23MTCR 23

CAN

04/09/23 57

Consumer Mailbox Handling

SAM7A3 / SAM7X -


MTCR 23


MRDY 23

Mailbox Transfer Command MTCR = 1: Allows to send a remote frame.

Then, waits automatically for a data frame from a producer mailbox. MRDY remains at 0 as long as the data frame has not been received or aborted.

CAN

04/09/23 58

Multiple Transfer or Abort Requests

SAM7A3 / SAM7X -

The CAN Transfer Command Register (CAN_TCR) allows to perform several transfer requests at the same time.

The CAN Abort Command Register (CAN_ACR) allows to perform several abort requests at the same time.

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At91sam7 - Can