@@ -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 SYSFS files to set and 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
============================================================================
@@ -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
------------------------
@@ -613,53 +620,178 @@ solution for a couple of reasons:
- 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- The tool 'vcan' from the SocketCAN SVN repository on BerliOS is obsolete.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
-
- On the project website http://developer.berlios.de/projects/socketcan
- there are different drivers available:
-
- 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)
-
- 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
-
- Please check the Mailing Lists on the berlios OSS project website.
-
- 6.6 todo
-
- 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.
-
-7. Credits
+ 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 CAN devices, like setting the bit-timing parameters, through
+ SYSFS files. They are described in the following chapter. 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 SYSFS files to set and get devices properties
+
+ When the CAN device is registered, a set of SYSFS files is created in
+ "/sys/class/net/canX/". These files allow to set and get device
+ properties. Here is a list of the files and a brief explanation for
+ what they are good for:
+
+ can_state:
+ Returns the current state of the CAN controller: "active",
+ "stopped" or "sleeping" or the bus error states "bus-warn",
+ "bus-pass" or "bus-off". Please do not read it frequently.
+ State changes are also reported via CAN error frames and the
+ application should monitor and handle them instead (see also
+ chapter 3.4).
+
+ can_ctrlmode:
+ Allows to set various CAN controller modes like loop-back (0x1),
+ listen-only (0x2) or triple-sampling (0x4) by writing the
+ corresponding bit mask to this file. Please use the prefix "0x"
+ for hexadecimal values.
+
+ can_echo:
+ Allows to read and toggle the local loop-back functionality of
+ the device. See chapter 6.2 for further information.
+
+ can_restart:
+ Writing "1" to this file allows to manually trigger a restart of
+ the CAN controller in case of a bus-off condition. This file is
+ not readable.
+
+ can_restart_ms:
+ Allows to set and get the automatic restart delay time. If set to
+ a value greater than 0, 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.
+
+ can_bittiming:
+ Sub-directory with files to set and get CAN bit-timing
+ parameters.
+
+ can_bittiming/bitrate
+ can_bittiming/sample_point:
+ If calculation of CAN bit-timing parameters is enabled in the
+ kernel (CONFIG_CAN_CALC_BITTIMING=y), the bit-timing can be
+ defined by writing the bit-rate in bits/sec to "bitrate".
+ Otherwise the file is read-only and returns the actual bit-rate.
+ Accordingly the sample-point in one-tenth of a percent can be
+ set or read. By default it's set to 0 using CIA-recommended
+ sample-points.
+
+ can_bittiming/tq
+ can_bittiming/prop_seg
+ can_bittiming/phase_seg1
+ can_bittiming/phase_seg2
+ can_bittiming/sjw:
+ These files allow to define the CAN bit-timing in a hardware
+ independent format as proposed by the Bosch CAN 2.0
+ specification.
+
+ can_bittiming/hw_clock
+ can_bittiming/hw_brp_inc
+ can_bittiming/hw_brp_max
+ can_bittiming/hw_brp_min
+ can_bittiming/hw_sjw_max
+ can_bittiming/hw_tseg1_max
+ can_bittiming/hw_tseg1_min
+ can_bittiming/hw_tseg2_max
+ can_bittiming/hw_tseg2_min:
+ These read-only files list the bit-timing constants for this
+ device. They are provided by the CAN controller driver and are
+ used to calculate and check CAN bit-timing parameters.
+ Furthermore, these values can be used for user-defined
+ (non-standard) bit-timing calculation algorithms in userspace.
+
+ can_statistics
+ can_statistics/arbitration_lost
+ can_statistics/bus_error
+ can_statistics/data_overrun
+ can_statistics/error_passive
+ can_statistics/error_warning
+ can_statistics/restarts
+ can_statistics/wakeup:
+ These read-only files list CAN specific statistics values.
+
+ 6.5.2 Setting the CAN bit-timing
+
+ The CAN bit-timing parameters can always be specified in a hardware
+ independent format as proposed in the Bosch CAN 2.0 specification
+ using the SYSFS files "tq", "prop_seg", "phase_seg1", "phase_seg2"
+ and "sjw". The SYSFS files are described in the previous chapter.
+
+ If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
+ recommended CAN bit-timing parameters will be calculated for the bit-
+ rate written to the SYSFS file "bitrate" when the device gets started.
+ Note that this works fine for the most common CAN controllers with
+ standard bit-rates but may *fail* for exotic bit-rates or CAN source
+ 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 available in the
+ SYSFS directory "can_bittiming" as well with the name prefix "hw_".
+
+ 6.5.3 Starting and stopping the CAN network device
+
+ A CAN network device is started and stopped as usual with the command
+ "ifconfig canX up" and "ifconfig canX 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:
+
+ # echo 125000 > /sys/class/net/can0/can_bittiming/bitrate
+ # ifconfig can0 up
+
+ A device may enter "bus-off" state if too much errors occurred on the
+ CAN bus. Then no more messages can be received or sent. The SYSFS file
+ "/sys/class/net/can0/can_state" then reports "bus-off". An automatic
+ bus-off recovery can be enabled by writing the desired restart delay
+ in milliseconds to "/sys/class/net/canX/can_restart_ms".
+ Alternatively, the application may realize the "bus-off" condition
+ by monitoring CAN error frames and do a restart when appropriate by
+ writing to the SYSFS file /sys/class/net/canX/can_restart. Note that
+ a restart will also create a CAN error frame (see also chapter 3.4).
+
+ 6.6 Supported CAN hardware
+
+ 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.
+
+7. Socket CAN resources
+-----------------------
+
+ 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:
+
+ http://developer.berlios.de/projects/socketcan
+
+ 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.
+
+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)