forked from Minki/linux
can: Documentation for the CAN device driver interface
This patch documents the CAN netowrk device drivers interface, removes obsolete documentation and adds some useful links to CAN resources. Signed-off-by: Wolfgang Grandegger <wg@grandegger.com> Signed-off-by: Oliver Hartkopp <oliver.hartkopp@volkswagen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Wolfgang Grandegger
David S. Miller
parent
a6286ee630
commit
e20dad964a
@ -36,10 +36,15 @@ This file contains
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6.2 local loopback of sent frames
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6.3 CAN controller hardware filters
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6.4 The virtual CAN driver (vcan)
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6.5 currently supported CAN hardware
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6.6 todo
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6.5 The CAN network device driver interface
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6.5.1 Netlink interface to set/get devices properties
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6.5.2 Setting the CAN bit-timing
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6.5.3 Starting and stopping the CAN network device
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6.6 supported CAN hardware
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7 Credits
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7 Socket CAN resources
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8 Credits
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============================================================================
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@ -234,6 +239,8 @@ solution for a couple of reasons:
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the user application using the common CAN filter mechanisms. Inside
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this filter definition the (interested) type of errors may be
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selected. The reception of error frames is disabled by default.
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The format of the CAN error frame is briefly decribed in the Linux
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header file "include/linux/can/error.h".
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4. How to use Socket CAN
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------------------------
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@ -605,61 +612,213 @@ solution for a couple of reasons:
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removal of vcan network devices can be managed with the ip(8) tool:
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- Create a virtual CAN network interface:
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ip link add type vcan
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$ ip link add type vcan
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- Create a virtual CAN network interface with a specific name 'vcan42':
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ip link add dev vcan42 type vcan
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$ ip link add dev vcan42 type vcan
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- Remove a (virtual CAN) network interface 'vcan42':
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ip link del vcan42
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$ ip link del vcan42
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The tool 'vcan' from the SocketCAN SVN repository on BerliOS is obsolete.
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6.5 The CAN network device driver interface
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Virtual CAN network device creation in older Kernels:
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In Linux Kernel versions < 2.6.24 the vcan driver creates 4 vcan
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netdevices at module load time by default. This value can be changed
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with the module parameter 'numdev'. E.g. 'modprobe vcan numdev=8'
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The CAN network device driver interface provides a generic interface
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to setup, configure and monitor CAN network devices. The user can then
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configure the CAN device, like setting the bit-timing parameters, via
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the netlink interface using the program "ip" from the "IPROUTE2"
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utility suite. The following chapter describes briefly how to use it.
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Furthermore, the interface uses a common data structure and exports a
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set of common functions, which all real CAN network device drivers
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should use. Please have a look to the SJA1000 or MSCAN driver to
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understand how to use them. The name of the module is can-dev.ko.
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6.5 currently supported CAN hardware
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6.5.1 Netlink interface to set/get devices properties
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On the project website http://developer.berlios.de/projects/socketcan
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there are different drivers available:
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The CAN device must be configured via netlink interface. The supported
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netlink message types are defined and briefly described in
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"include/linux/can/netlink.h". CAN link support for the program "ip"
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of the IPROUTE2 utility suite is avaiable and it can be used as shown
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below:
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vcan: Virtual CAN interface driver (if no real hardware is available)
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sja1000: Philips SJA1000 CAN controller (recommended)
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i82527: Intel i82527 CAN controller
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mscan: Motorola/Freescale CAN controller (e.g. inside SOC MPC5200)
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ccan: CCAN controller core (e.g. inside SOC h7202)
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slcan: For a bunch of CAN adaptors that are attached via a
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serial line ASCII protocol (for serial / USB adaptors)
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- Setting CAN device properties:
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Additionally the different CAN adaptors (ISA/PCI/PCMCIA/USB/Parport)
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from PEAK Systemtechnik support the CAN netdevice driver model
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since Linux driver v6.0: http://www.peak-system.com/linux/index.htm
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$ ip link set can0 type can help
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Usage: ip link set DEVICE type can
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[ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
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[ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
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phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
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Please check the Mailing Lists on the berlios OSS project website.
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[ loopback { on | off } ]
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[ listen-only { on | off } ]
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[ triple-sampling { on | off } ]
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6.6 todo
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[ restart-ms TIME-MS ]
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[ restart ]
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The configuration interface for CAN network drivers is still an open
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issue that has not been finalized in the socketcan project. Also the
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idea of having a library module (candev.ko) that holds functions
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that are needed by all CAN netdevices is not ready to ship.
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Your contribution is welcome.
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Where: BITRATE := { 1..1000000 }
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SAMPLE-POINT := { 0.000..0.999 }
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TQ := { NUMBER }
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PROP-SEG := { 1..8 }
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PHASE-SEG1 := { 1..8 }
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PHASE-SEG2 := { 1..8 }
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SJW := { 1..4 }
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RESTART-MS := { 0 | NUMBER }
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7. Credits
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- Display CAN device details and statistics:
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$ ip -details -statistics link show can0
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2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
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link/can
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can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
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bitrate 125000 sample_point 0.875
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tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
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sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
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clock 8000000
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re-started bus-errors arbit-lost error-warn error-pass bus-off
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41 17457 0 41 42 41
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RX: bytes packets errors dropped overrun mcast
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140859 17608 17457 0 0 0
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TX: bytes packets errors dropped carrier collsns
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861 112 0 41 0 0
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More info to the above output:
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"<TRIPLE-SAMPLING>"
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Shows the list of selected CAN controller modes: LOOPBACK,
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LISTEN-ONLY, or TRIPLE-SAMPLING.
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"state ERROR-ACTIVE"
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The current state of the CAN controller: "ERROR-ACTIVE",
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"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
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"restart-ms 100"
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Automatic restart delay time. If set to a non-zero value, a
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restart of the CAN controller will be triggered automatically
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in case of a bus-off condition after the specified delay time
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in milliseconds. By default it's off.
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"bitrate 125000 sample_point 0.875"
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Shows the real bit-rate in bits/sec and the sample-point in the
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range 0.000..0.999. If the calculation of bit-timing parameters
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is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
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bit-timing can be defined by setting the "bitrate" argument.
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Optionally the "sample-point" can be specified. By default it's
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0.000 assuming CIA-recommended sample-points.
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"tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
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Shows the time quanta in ns, propagation segment, phase buffer
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segment 1 and 2 and the synchronisation jump width in units of
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tq. They allow to define the CAN bit-timing in a hardware
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independent format as proposed by the Bosch CAN 2.0 spec (see
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chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
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"sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
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clock 8000000"
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Shows the bit-timing constants of the CAN controller, here the
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"sja1000". The minimum and maximum values of the time segment 1
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and 2, the synchronisation jump width in units of tq, the
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bitrate pre-scaler and the CAN system clock frequency in Hz.
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These constants could be used for user-defined (non-standard)
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bit-timing calculation algorithms in user-space.
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"re-started bus-errors arbit-lost error-warn error-pass bus-off"
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Shows the number of restarts, bus and arbitration lost errors,
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and the state changes to the error-warning, error-passive and
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bus-off state. RX overrun errors are listed in the "overrun"
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field of the standard network statistics.
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6.5.2 Setting the CAN bit-timing
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The CAN bit-timing parameters can always be defined in a hardware
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independent format as proposed in the Bosch CAN 2.0 specification
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specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
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and "sjw":
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$ ip link set canX type can tq 125 prop-seg 6 \
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phase-seg1 7 phase-seg2 2 sjw 1
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If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
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recommended CAN bit-timing parameters will be calculated if the bit-
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rate is specified with the argument "bitrate":
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$ ip link set canX type can bitrate 125000
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Note that this works fine for the most common CAN controllers with
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standard bit-rates but may *fail* for exotic bit-rates or CAN system
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clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
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space and allows user-space tools to solely determine and set the
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bit-timing parameters. The CAN controller specific bit-timing
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constants can be used for that purpose. They are listed by the
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following command:
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$ ip -details link show can0
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...
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sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
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6.5.3 Starting and stopping the CAN network device
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A CAN network device is started or stopped as usual with the command
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"ifconfig canX up/down" or "ip link set canX up/down". Be aware that
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you *must* define proper bit-timing parameters for real CAN devices
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before you can start it to avoid error-prone default settings:
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$ ip link set canX up type can bitrate 125000
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A device may enter the "bus-off" state if too much errors occurred on
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the CAN bus. Then no more messages are received or sent. An automatic
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bus-off recovery can be enabled by setting the "restart-ms" to a
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non-zero value, e.g.:
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$ ip link set canX type can restart-ms 100
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Alternatively, the application may realize the "bus-off" condition
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by monitoring CAN error frames and do a restart when appropriate with
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the command:
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$ ip link set canX type can restart
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Note that a restart will also create a CAN error frame (see also
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chapter 3.4).
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6.6 Supported CAN hardware
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Please check the "Kconfig" file in "drivers/net/can" to get an actual
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list of the support CAN hardware. On the Socket CAN project website
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(see chapter 7) there might be further drivers available, also for
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older kernel versions.
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7. Socket CAN resources
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-----------------------
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You can find further resources for Socket CAN like user space tools,
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support for old kernel versions, more drivers, mailing lists, etc.
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at the BerliOS OSS project website for Socket CAN:
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http://developer.berlios.de/projects/socketcan
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If you have questions, bug fixes, etc., don't hesitate to post them to
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the Socketcan-Users mailing list. But please search the archives first.
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8. Credits
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----------
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Oliver Hartkopp (PF_CAN core, filters, drivers, bcm)
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Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
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Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
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Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
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Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews)
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Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
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CAN device driver interface, MSCAN driver)
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Robert Schwebel (design reviews, PTXdist integration)
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Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
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Benedikt Spranger (reviews)
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Thomas Gleixner (LKML reviews, coding style, posting hints)
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Andrey Volkov (kernel subtree structure, ioctls, mscan driver)
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Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
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Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
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Klaus Hitschler (PEAK driver integration)
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Uwe Koppe (CAN netdevices with PF_PACKET approach)
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Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
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Pavel Pisa (Bit-timing calculation)
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Sascha Hauer (SJA1000 platform driver)
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Sebastian Haas (SJA1000 EMS PCI driver)
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Markus Plessing (SJA1000 EMS PCI driver)
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Per Dalen (SJA1000 Kvaser PCI driver)
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Sam Ravnborg (reviews, coding style, kbuild help)
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