+ $ ip link del vcan42
+
+ 6.5 The CAN network device driver interface
+
+ The CAN network device driver interface provides a generic interface
+ to setup, configure and monitor CAN network devices. The user can then
+ configure the CAN device, like setting the bit-timing parameters, via
+ the netlink interface using the program "ip" from the "IPROUTE2"
+ utility suite. The following chapter describes briefly how to use it.
+ Furthermore, the interface uses a common data structure and exports a
+ set of common functions, which all real CAN network device drivers
+ should use. Please have a look to the SJA1000 or MSCAN driver to
+ understand how to use them. The name of the module is can-dev.ko.
+
+ 6.5.1 Netlink interface to set/get devices properties
+
+ The CAN device must be configured via netlink interface. The supported
+ netlink message types are defined and briefly described in
+ "include/linux/can/netlink.h". CAN link support for the program "ip"
+ of the IPROUTE2 utility suite is avaiable and it can be used as shown
+ below:
+
+ - Setting CAN device properties:
+
+ $ ip link set can0 type can help
+ Usage: ip link set DEVICE type can
+ [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
+ [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
+ phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
+
+ [ loopback { on | off } ]
+ [ listen-only { on | off } ]
+ [ triple-sampling { on | off } ]
+
+ [ restart-ms TIME-MS ]
+ [ restart ]
+
+ Where: BITRATE := { 1..1000000 }
+ SAMPLE-POINT := { 0.000..0.999 }
+ TQ := { NUMBER }
+ PROP-SEG := { 1..8 }
+ PHASE-SEG1 := { 1..8 }
+ PHASE-SEG2 := { 1..8 }
+ SJW := { 1..4 }
+ RESTART-MS := { 0 | NUMBER }
+
+ - Display CAN device details and statistics:
+
+ $ ip -details -statistics link show can0
+ 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
+ link/can
+ can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
+ bitrate 125000 sample_point 0.875
+ tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
+ sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
+ clock 8000000
+ re-started bus-errors arbit-lost error-warn error-pass bus-off
+ 41 17457 0 41 42 41
+ RX: bytes packets errors dropped overrun mcast
+ 140859 17608 17457 0 0 0
+ TX: bytes packets errors dropped carrier collsns
+ 861 112 0 41 0 0
+
+ More info to the above output:
+
+ "<TRIPLE-SAMPLING>"
+ Shows the list of selected CAN controller modes: LOOPBACK,
+ LISTEN-ONLY, or TRIPLE-SAMPLING.
+
+ "state ERROR-ACTIVE"
+ The current state of the CAN controller: "ERROR-ACTIVE",
+ "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
+
+ "restart-ms 100"
+ Automatic restart delay time. If set to a non-zero value, a
+ restart of the CAN controller will be triggered automatically
+ in case of a bus-off condition after the specified delay time
+ in milliseconds. By default it's off.
+
+ "bitrate 125000 sample_point 0.875"
+ Shows the real bit-rate in bits/sec and the sample-point in the
+ range 0.000..0.999. If the calculation of bit-timing parameters
+ is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
+ bit-timing can be defined by setting the "bitrate" argument.
+ Optionally the "sample-point" can be specified. By default it's
+ 0.000 assuming CIA-recommended sample-points.
+
+ "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
+ Shows the time quanta in ns, propagation segment, phase buffer
+ segment 1 and 2 and the synchronisation jump width in units of
+ tq. They allow to define the CAN bit-timing in a hardware
+ independent format as proposed by the Bosch CAN 2.0 spec (see
+ chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
+
+ "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
+ clock 8000000"
+ Shows the bit-timing constants of the CAN controller, here the
+ "sja1000". The minimum and maximum values of the time segment 1
+ and 2, the synchronisation jump width in units of tq, the
+ bitrate pre-scaler and the CAN system clock frequency in Hz.
+ These constants could be used for user-defined (non-standard)
+ bit-timing calculation algorithms in user-space.
+
+ "re-started bus-errors arbit-lost error-warn error-pass bus-off"
+ Shows the number of restarts, bus and arbitration lost errors,
+ and the state changes to the error-warning, error-passive and
+ bus-off state. RX overrun errors are listed in the "overrun"
+ field of the standard network statistics.
+
+ 6.5.2 Setting the CAN bit-timing
+
+ The CAN bit-timing parameters can always be defined in a hardware
+ independent format as proposed in the Bosch CAN 2.0 specification
+ specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
+ and "sjw":
+
+ $ ip link set canX type can tq 125 prop-seg 6 \
+ phase-seg1 7 phase-seg2 2 sjw 1
+
+ If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
+ recommended CAN bit-timing parameters will be calculated if the bit-
+ rate is specified with the argument "bitrate":
+
+ $ ip link set canX type can bitrate 125000
+
+ Note that this works fine for the most common CAN controllers with
+ standard bit-rates but may *fail* for exotic bit-rates or CAN system
+ clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
+ space and allows user-space tools to solely determine and set the
+ bit-timing parameters. The CAN controller specific bit-timing
+ constants can be used for that purpose. They are listed by the
+ following command:
+
+ $ ip -details link show can0
+ ...
+ sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
+
+ 6.5.3 Starting and stopping the CAN network device
+
+ A CAN network device is started or stopped as usual with the command
+ "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
+ you *must* define proper bit-timing parameters for real CAN devices
+ before you can start it to avoid error-prone default settings:
+
+ $ ip link set canX up type can bitrate 125000
+
+ A device may enter the "bus-off" state if too much errors occurred on
+ the CAN bus. Then no more messages are received or sent. An automatic
+ bus-off recovery can be enabled by setting the "restart-ms" to a
+ non-zero value, e.g.:
+
+ $ ip link set canX type can restart-ms 100
+
+ Alternatively, the application may realize the "bus-off" condition
+ by monitoring CAN error frames and do a restart when appropriate with
+ the command:
+
+ $ ip link set canX type can restart
+
+ Note that a restart will also create a CAN error frame (see also
+ chapter 3.4).
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