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can: Documentation for the CAN device driver interface
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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>
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Wolfgang Grandegger authored and David S. Miller committed May 18, 2009
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235 changes: 197 additions & 38 deletions Documentation/networking/can.txt
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Expand Up @@ -36,10 +36,15 @@ This file contains
6.2 local loopback of sent frames
6.3 CAN controller hardware filters
6.4 The virtual CAN driver (vcan)
6.5 currently supported CAN hardware
6.6 todo
6.5 The CAN network device driver interface
6.5.1 Netlink interface to set/get devices properties
6.5.2 Setting the CAN bit-timing
6.5.3 Starting and stopping the CAN network device
6.6 supported CAN hardware

7 Credits
7 Socket CAN resources

8 Credits

============================================================================

Expand Down Expand Up @@ -234,6 +239,8 @@ solution for a couple of reasons:
the user application using the common CAN filter mechanisms. Inside
this filter definition the (interested) type of errors may be
selected. The reception of error frames is disabled by default.
The format of the CAN error frame is briefly decribed in the Linux
header file "include/linux/can/error.h".

4. How to use Socket CAN
------------------------
Expand Down Expand Up @@ -605,61 +612,213 @@ solution for a couple of reasons:
removal of vcan network devices can be managed with the ip(8) tool:

- Create a virtual CAN network interface:
ip link add type vcan
$ ip link add type vcan

- Create a virtual CAN network interface with a specific name 'vcan42':
ip link add dev vcan42 type vcan
$ ip link add dev vcan42 type vcan

- Remove a (virtual CAN) network interface 'vcan42':
ip link del vcan42

The tool 'vcan' from the SocketCAN SVN repository on BerliOS is obsolete.

Virtual CAN network device creation in older Kernels:
In Linux Kernel versions < 2.6.24 the vcan driver creates 4 vcan
netdevices at module load time by default. This value can be changed
with the module parameter 'numdev'. E.g. 'modprobe vcan numdev=8'

6.5 currently supported CAN hardware
$ 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).

On the project website http://developer.berlios.de/projects/socketcan
there are different drivers available:
6.6 Supported CAN hardware

vcan: Virtual CAN interface driver (if no real hardware is available)
sja1000: Philips SJA1000 CAN controller (recommended)
i82527: Intel i82527 CAN controller
mscan: Motorola/Freescale CAN controller (e.g. inside SOC MPC5200)
ccan: CCAN controller core (e.g. inside SOC h7202)
slcan: For a bunch of CAN adaptors that are attached via a
serial line ASCII protocol (for serial / USB adaptors)
Please check the "Kconfig" file in "drivers/net/can" to get an actual
list of the support CAN hardware. On the Socket CAN project website
(see chapter 7) there might be further drivers available, also for
older kernel versions.

Additionally the different CAN adaptors (ISA/PCI/PCMCIA/USB/Parport)
from PEAK Systemtechnik support the CAN netdevice driver model
since Linux driver v6.0: http://www.peak-system.com/linux/index.htm
7. Socket CAN resources
-----------------------

Please check the Mailing Lists on the berlios OSS project website.
You can find further resources for Socket CAN like user space tools,
support for old kernel versions, more drivers, mailing lists, etc.
at the BerliOS OSS project website for Socket CAN:

6.6 todo
http://developer.berlios.de/projects/socketcan

The configuration interface for CAN network drivers is still an open
issue that has not been finalized in the socketcan project. Also the
idea of having a library module (candev.ko) that holds functions
that are needed by all CAN netdevices is not ready to ship.
Your contribution is welcome.
If you have questions, bug fixes, etc., don't hesitate to post them to
the Socketcan-Users mailing list. But please search the archives first.

7. Credits
8. Credits
----------

Oliver Hartkopp (PF_CAN core, filters, drivers, bcm)
Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews)
Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
CAN device driver interface, MSCAN driver)
Robert Schwebel (design reviews, PTXdist integration)
Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
Benedikt Spranger (reviews)
Thomas Gleixner (LKML reviews, coding style, posting hints)
Andrey Volkov (kernel subtree structure, ioctls, mscan driver)
Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
Klaus Hitschler (PEAK driver integration)
Uwe Koppe (CAN netdevices with PF_PACKET approach)
Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
Pavel Pisa (Bit-timing calculation)
Sascha Hauer (SJA1000 platform driver)
Sebastian Haas (SJA1000 EMS PCI driver)
Markus Plessing (SJA1000 EMS PCI driver)
Per Dalen (SJA1000 Kvaser PCI driver)
Sam Ravnborg (reviews, coding style, kbuild help)

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