aboutsummaryrefslogtreecommitdiff
path: root/Documentation/networking/can.txt
diff options
context:
space:
mode:
authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
commit3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a (patch)
treeb9996006addfd7ae70a39672b76843b49aebc189 /Documentation/networking/can.txt
downloadlinux-linaro-highbank-3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a.tar.gz
Imported Upstream version 3.9.0HEADupstream/3.9.0upstreammaster
Diffstat (limited to 'Documentation/networking/can.txt')
-rw-r--r--Documentation/networking/can.txt974
1 files changed, 974 insertions, 0 deletions
diff --git a/Documentation/networking/can.txt b/Documentation/networking/can.txt
new file mode 100644
index 00000000..820f5534
--- /dev/null
+++ b/Documentation/networking/can.txt
@@ -0,0 +1,974 @@
+============================================================================
+
+can.txt
+
+Readme file for the Controller Area Network Protocol Family (aka Socket CAN)
+
+This file contains
+
+ 1 Overview / What is Socket CAN
+
+ 2 Motivation / Why using the socket API
+
+ 3 Socket CAN concept
+ 3.1 receive lists
+ 3.2 local loopback of sent frames
+ 3.3 network security issues (capabilities)
+ 3.4 network problem notifications
+
+ 4 How to use Socket CAN
+ 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
+ 4.1.1 RAW socket option CAN_RAW_FILTER
+ 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
+ 4.1.3 RAW socket option CAN_RAW_LOOPBACK
+ 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
+ 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
+ 4.1.6 RAW socket returned message flags
+ 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
+ 4.3 connected transport protocols (SOCK_SEQPACKET)
+ 4.4 unconnected transport protocols (SOCK_DGRAM)
+
+ 5 Socket CAN core module
+ 5.1 can.ko module params
+ 5.2 procfs content
+ 5.3 writing own CAN protocol modules
+
+ 6 CAN network drivers
+ 6.1 general settings
+ 6.2 local loopback of sent frames
+ 6.3 CAN controller hardware filters
+ 6.4 The virtual CAN driver (vcan)
+ 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 CAN FD (flexible data rate) driver support
+ 6.7 supported CAN hardware
+
+ 7 Socket CAN resources
+
+ 8 Credits
+
+============================================================================
+
+1. Overview / What is Socket CAN
+--------------------------------
+
+The socketcan package is an implementation of CAN protocols
+(Controller Area Network) for Linux. CAN is a networking technology
+which has widespread use in automation, embedded devices, and
+automotive fields. While there have been other CAN implementations
+for Linux based on character devices, Socket CAN uses the Berkeley
+socket API, the Linux network stack and implements the CAN device
+drivers as network interfaces. The CAN socket API has been designed
+as similar as possible to the TCP/IP protocols to allow programmers,
+familiar with network programming, to easily learn how to use CAN
+sockets.
+
+2. Motivation / Why using the socket API
+----------------------------------------
+
+There have been CAN implementations for Linux before Socket CAN so the
+question arises, why we have started another project. Most existing
+implementations come as a device driver for some CAN hardware, they
+are based on character devices and provide comparatively little
+functionality. Usually, there is only a hardware-specific device
+driver which provides a character device interface to send and
+receive raw CAN frames, directly to/from the controller hardware.
+Queueing of frames and higher-level transport protocols like ISO-TP
+have to be implemented in user space applications. Also, most
+character-device implementations support only one single process to
+open the device at a time, similar to a serial interface. Exchanging
+the CAN controller requires employment of another device driver and
+often the need for adaption of large parts of the application to the
+new driver's API.
+
+Socket CAN was designed to overcome all of these limitations. A new
+protocol family has been implemented which provides a socket interface
+to user space applications and which builds upon the Linux network
+layer, so to use all of the provided queueing functionality. A device
+driver for CAN controller hardware registers itself with the Linux
+network layer as a network device, so that CAN frames from the
+controller can be passed up to the network layer and on to the CAN
+protocol family module and also vice-versa. Also, the protocol family
+module provides an API for transport protocol modules to register, so
+that any number of transport protocols can be loaded or unloaded
+dynamically. In fact, the can core module alone does not provide any
+protocol and cannot be used without loading at least one additional
+protocol module. Multiple sockets can be opened at the same time,
+on different or the same protocol module and they can listen/send
+frames on different or the same CAN IDs. Several sockets listening on
+the same interface for frames with the same CAN ID are all passed the
+same received matching CAN frames. An application wishing to
+communicate using a specific transport protocol, e.g. ISO-TP, just
+selects that protocol when opening the socket, and then can read and
+write application data byte streams, without having to deal with
+CAN-IDs, frames, etc.
+
+Similar functionality visible from user-space could be provided by a
+character device, too, but this would lead to a technically inelegant
+solution for a couple of reasons:
+
+* Intricate usage. Instead of passing a protocol argument to
+ socket(2) and using bind(2) to select a CAN interface and CAN ID, an
+ application would have to do all these operations using ioctl(2)s.
+
+* Code duplication. A character device cannot make use of the Linux
+ network queueing code, so all that code would have to be duplicated
+ for CAN networking.
+
+* Abstraction. In most existing character-device implementations, the
+ hardware-specific device driver for a CAN controller directly
+ provides the character device for the application to work with.
+ This is at least very unusual in Unix systems for both, char and
+ block devices. For example you don't have a character device for a
+ certain UART of a serial interface, a certain sound chip in your
+ computer, a SCSI or IDE controller providing access to your hard
+ disk or tape streamer device. Instead, you have abstraction layers
+ which provide a unified character or block device interface to the
+ application on the one hand, and a interface for hardware-specific
+ device drivers on the other hand. These abstractions are provided
+ by subsystems like the tty layer, the audio subsystem or the SCSI
+ and IDE subsystems for the devices mentioned above.
+
+ The easiest way to implement a CAN device driver is as a character
+ device without such a (complete) abstraction layer, as is done by most
+ existing drivers. The right way, however, would be to add such a
+ layer with all the functionality like registering for certain CAN
+ IDs, supporting several open file descriptors and (de)multiplexing
+ CAN frames between them, (sophisticated) queueing of CAN frames, and
+ providing an API for device drivers to register with. However, then
+ it would be no more difficult, or may be even easier, to use the
+ networking framework provided by the Linux kernel, and this is what
+ Socket CAN does.
+
+ The use of the networking framework of the Linux kernel is just the
+ natural and most appropriate way to implement CAN for Linux.
+
+3. Socket CAN concept
+---------------------
+
+ As described in chapter 2 it is the main goal of Socket CAN to
+ provide a socket interface to user space applications which builds
+ upon the Linux network layer. In contrast to the commonly known
+ TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
+ medium that has no MAC-layer addressing like ethernet. The CAN-identifier
+ (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
+ have to be chosen uniquely on the bus. When designing a CAN-ECU
+ network the CAN-IDs are mapped to be sent by a specific ECU.
+ For this reason a CAN-ID can be treated best as a kind of source address.
+
+ 3.1 receive lists
+
+ The network transparent access of multiple applications leads to the
+ problem that different applications may be interested in the same
+ CAN-IDs from the same CAN network interface. The Socket CAN core
+ module - which implements the protocol family CAN - provides several
+ high efficient receive lists for this reason. If e.g. a user space
+ application opens a CAN RAW socket, the raw protocol module itself
+ requests the (range of) CAN-IDs from the Socket CAN core that are
+ requested by the user. The subscription and unsubscription of
+ CAN-IDs can be done for specific CAN interfaces or for all(!) known
+ CAN interfaces with the can_rx_(un)register() functions provided to
+ CAN protocol modules by the SocketCAN core (see chapter 5).
+ To optimize the CPU usage at runtime the receive lists are split up
+ into several specific lists per device that match the requested
+ filter complexity for a given use-case.
+
+ 3.2 local loopback of sent frames
+
+ As known from other networking concepts the data exchanging
+ applications may run on the same or different nodes without any
+ change (except for the according addressing information):
+
+ ___ ___ ___ _______ ___
+ | _ | | _ | | _ | | _ _ | | _ |
+ ||A|| ||B|| ||C|| ||A| |B|| ||C||
+ |___| |___| |___| |_______| |___|
+ | | | | |
+ -----------------(1)- CAN bus -(2)---------------
+
+ To ensure that application A receives the same information in the
+ example (2) as it would receive in example (1) there is need for
+ some kind of local loopback of the sent CAN frames on the appropriate
+ node.
+
+ The Linux network devices (by default) just can handle the
+ transmission and reception of media dependent frames. Due to the
+ arbitration on the CAN bus the transmission of a low prio CAN-ID
+ may be delayed by the reception of a high prio CAN frame. To
+ reflect the correct* traffic on the node the loopback of the sent
+ data has to be performed right after a successful transmission. If
+ the CAN network interface is not capable of performing the loopback for
+ some reason the SocketCAN core can do this task as a fallback solution.
+ See chapter 6.2 for details (recommended).
+
+ The loopback functionality is enabled by default to reflect standard
+ networking behaviour for CAN applications. Due to some requests from
+ the RT-SocketCAN group the loopback optionally may be disabled for each
+ separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
+
+ * = you really like to have this when you're running analyser tools
+ like 'candump' or 'cansniffer' on the (same) node.
+
+ 3.3 network security issues (capabilities)
+
+ The Controller Area Network is a local field bus transmitting only
+ broadcast messages without any routing and security concepts.
+ In the majority of cases the user application has to deal with
+ raw CAN frames. Therefore it might be reasonable NOT to restrict
+ the CAN access only to the user root, as known from other networks.
+ Since the currently implemented CAN_RAW and CAN_BCM sockets can only
+ send and receive frames to/from CAN interfaces it does not affect
+ security of others networks to allow all users to access the CAN.
+ To enable non-root users to access CAN_RAW and CAN_BCM protocol
+ sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be
+ selected at kernel compile time.
+
+ 3.4 network problem notifications
+
+ The use of the CAN bus may lead to several problems on the physical
+ and media access control layer. Detecting and logging of these lower
+ layer problems is a vital requirement for CAN users to identify
+ hardware issues on the physical transceiver layer as well as
+ arbitration problems and error frames caused by the different
+ ECUs. The occurrence of detected errors are important for diagnosis
+ and have to be logged together with the exact timestamp. For this
+ reason the CAN interface driver can generate so called Error Message
+ Frames that can optionally be passed to the user application in the
+ same way as other CAN frames. Whenever an error on the physical layer
+ or the MAC layer is detected (e.g. by the CAN controller) the driver
+ creates an appropriate error message frame. Error messages frames can
+ be requested by 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 messages is disabled
+ by default. The format of the CAN error message frame is briefly
+ described in the Linux header file "include/linux/can/error.h".
+
+4. How to use Socket CAN
+------------------------
+
+ Like TCP/IP, you first need to open a socket for communicating over a
+ CAN network. Since Socket CAN implements a new protocol family, you
+ need to pass PF_CAN as the first argument to the socket(2) system
+ call. Currently, there are two CAN protocols to choose from, the raw
+ socket protocol and the broadcast manager (BCM). So to open a socket,
+ you would write
+
+ s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+ and
+
+ s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
+
+ respectively. After the successful creation of the socket, you would
+ normally use the bind(2) system call to bind the socket to a CAN
+ interface (which is different from TCP/IP due to different addressing
+ - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
+ the socket, you can read(2) and write(2) from/to the socket or use
+ send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
+ on the socket as usual. There are also CAN specific socket options
+ described below.
+
+ The basic CAN frame structure and the sockaddr structure are defined
+ in include/linux/can.h:
+
+ struct can_frame {
+ canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+ __u8 can_dlc; /* frame payload length in byte (0 .. 8) */
+ __u8 data[8] __attribute__((aligned(8)));
+ };
+
+ The alignment of the (linear) payload data[] to a 64bit boundary
+ allows the user to define own structs and unions to easily access the
+ CAN payload. There is no given byteorder on the CAN bus by
+ default. A read(2) system call on a CAN_RAW socket transfers a
+ struct can_frame to the user space.
+
+ The sockaddr_can structure has an interface index like the
+ PF_PACKET socket, that also binds to a specific interface:
+
+ struct sockaddr_can {
+ sa_family_t can_family;
+ int can_ifindex;
+ union {
+ /* transport protocol class address info (e.g. ISOTP) */
+ struct { canid_t rx_id, tx_id; } tp;
+
+ /* reserved for future CAN protocols address information */
+ } can_addr;
+ };
+
+ To determine the interface index an appropriate ioctl() has to
+ be used (example for CAN_RAW sockets without error checking):
+
+ int s;
+ struct sockaddr_can addr;
+ struct ifreq ifr;
+
+ s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+ strcpy(ifr.ifr_name, "can0" );
+ ioctl(s, SIOCGIFINDEX, &ifr);
+
+ addr.can_family = AF_CAN;
+ addr.can_ifindex = ifr.ifr_ifindex;
+
+ bind(s, (struct sockaddr *)&addr, sizeof(addr));
+
+ (..)
+
+ To bind a socket to all(!) CAN interfaces the interface index must
+ be 0 (zero). In this case the socket receives CAN frames from every
+ enabled CAN interface. To determine the originating CAN interface
+ the system call recvfrom(2) may be used instead of read(2). To send
+ on a socket that is bound to 'any' interface sendto(2) is needed to
+ specify the outgoing interface.
+
+ Reading CAN frames from a bound CAN_RAW socket (see above) consists
+ of reading a struct can_frame:
+
+ struct can_frame frame;
+
+ nbytes = read(s, &frame, sizeof(struct can_frame));
+
+ if (nbytes < 0) {
+ perror("can raw socket read");
+ return 1;
+ }
+
+ /* paranoid check ... */
+ if (nbytes < sizeof(struct can_frame)) {
+ fprintf(stderr, "read: incomplete CAN frame\n");
+ return 1;
+ }
+
+ /* do something with the received CAN frame */
+
+ Writing CAN frames can be done similarly, with the write(2) system call:
+
+ nbytes = write(s, &frame, sizeof(struct can_frame));
+
+ When the CAN interface is bound to 'any' existing CAN interface
+ (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
+ information about the originating CAN interface is needed:
+
+ struct sockaddr_can addr;
+ struct ifreq ifr;
+ socklen_t len = sizeof(addr);
+ struct can_frame frame;
+
+ nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
+ 0, (struct sockaddr*)&addr, &len);
+
+ /* get interface name of the received CAN frame */
+ ifr.ifr_ifindex = addr.can_ifindex;
+ ioctl(s, SIOCGIFNAME, &ifr);
+ printf("Received a CAN frame from interface %s", ifr.ifr_name);
+
+ To write CAN frames on sockets bound to 'any' CAN interface the
+ outgoing interface has to be defined certainly.
+
+ strcpy(ifr.ifr_name, "can0");
+ ioctl(s, SIOCGIFINDEX, &ifr);
+ addr.can_ifindex = ifr.ifr_ifindex;
+ addr.can_family = AF_CAN;
+
+ nbytes = sendto(s, &frame, sizeof(struct can_frame),
+ 0, (struct sockaddr*)&addr, sizeof(addr));
+
+ Remark about CAN FD (flexible data rate) support:
+
+ Generally the handling of CAN FD is very similar to the formerly described
+ examples. The new CAN FD capable CAN controllers support two different
+ bitrates for the arbitration phase and the payload phase of the CAN FD frame
+ and up to 64 bytes of payload. This extended payload length breaks all the
+ kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
+ bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
+ the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
+ switches the socket into a mode that allows the handling of CAN FD frames
+ and (legacy) CAN frames simultaneously (see section 4.1.5).
+
+ The struct canfd_frame is defined in include/linux/can.h:
+
+ struct canfd_frame {
+ canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+ __u8 len; /* frame payload length in byte (0 .. 64) */
+ __u8 flags; /* additional flags for CAN FD */
+ __u8 __res0; /* reserved / padding */
+ __u8 __res1; /* reserved / padding */
+ __u8 data[64] __attribute__((aligned(8)));
+ };
+
+ The struct canfd_frame and the existing struct can_frame have the can_id,
+ the payload length and the payload data at the same offset inside their
+ structures. This allows to handle the different structures very similar.
+ When the content of a struct can_frame is copied into a struct canfd_frame
+ all structure elements can be used as-is - only the data[] becomes extended.
+
+ When introducing the struct canfd_frame it turned out that the data length
+ code (DLC) of the struct can_frame was used as a length information as the
+ length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
+ the easy handling of the length information the canfd_frame.len element
+ contains a plain length value from 0 .. 64. So both canfd_frame.len and
+ can_frame.can_dlc are equal and contain a length information and no DLC.
+ For details about the distinction of CAN and CAN FD capable devices and
+ the mapping to the bus-relevant data length code (DLC), see chapter 6.6.
+
+ The length of the two CAN(FD) frame structures define the maximum transfer
+ unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
+ definitions are specified for CAN specific MTUs in include/linux/can.h :
+
+ #define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame
+ #define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame
+
+ 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
+
+ Using CAN_RAW sockets is extensively comparable to the commonly
+ known access to CAN character devices. To meet the new possibilities
+ provided by the multi user SocketCAN approach, some reasonable
+ defaults are set at RAW socket binding time:
+
+ - The filters are set to exactly one filter receiving everything
+ - The socket only receives valid data frames (=> no error message frames)
+ - The loopback of sent CAN frames is enabled (see chapter 3.2)
+ - The socket does not receive its own sent frames (in loopback mode)
+
+ These default settings may be changed before or after binding the socket.
+ To use the referenced definitions of the socket options for CAN_RAW
+ sockets, include <linux/can/raw.h>.
+
+ 4.1.1 RAW socket option CAN_RAW_FILTER
+
+ The reception of CAN frames using CAN_RAW sockets can be controlled
+ by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
+
+ The CAN filter structure is defined in include/linux/can.h:
+
+ struct can_filter {
+ canid_t can_id;
+ canid_t can_mask;
+ };
+
+ A filter matches, when
+
+ <received_can_id> & mask == can_id & mask
+
+ which is analogous to known CAN controllers hardware filter semantics.
+ The filter can be inverted in this semantic, when the CAN_INV_FILTER
+ bit is set in can_id element of the can_filter structure. In
+ contrast to CAN controller hardware filters the user may set 0 .. n
+ receive filters for each open socket separately:
+
+ struct can_filter rfilter[2];
+
+ rfilter[0].can_id = 0x123;
+ rfilter[0].can_mask = CAN_SFF_MASK;
+ rfilter[1].can_id = 0x200;
+ rfilter[1].can_mask = 0x700;
+
+ setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
+
+ To disable the reception of CAN frames on the selected CAN_RAW socket:
+
+ setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
+
+ To set the filters to zero filters is quite obsolete as not read
+ data causes the raw socket to discard the received CAN frames. But
+ having this 'send only' use-case we may remove the receive list in the
+ Kernel to save a little (really a very little!) CPU usage.
+
+ 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
+
+ As described in chapter 3.4 the CAN interface driver can generate so
+ called Error Message Frames that can optionally be passed to the user
+ application in the same way as other CAN frames. The possible
+ errors are divided into different error classes that may be filtered
+ using the appropriate error mask. To register for every possible
+ error condition CAN_ERR_MASK can be used as value for the error mask.
+ The values for the error mask are defined in linux/can/error.h .
+
+ can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
+
+ setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
+ &err_mask, sizeof(err_mask));
+
+ 4.1.3 RAW socket option CAN_RAW_LOOPBACK
+
+ To meet multi user needs the local loopback is enabled by default
+ (see chapter 3.2 for details). But in some embedded use-cases
+ (e.g. when only one application uses the CAN bus) this loopback
+ functionality can be disabled (separately for each socket):
+
+ int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
+
+ setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
+
+ 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
+
+ When the local loopback is enabled, all the sent CAN frames are
+ looped back to the open CAN sockets that registered for the CAN
+ frames' CAN-ID on this given interface to meet the multi user
+ needs. The reception of the CAN frames on the same socket that was
+ sending the CAN frame is assumed to be unwanted and therefore
+ disabled by default. This default behaviour may be changed on
+ demand:
+
+ int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
+
+ setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
+ &recv_own_msgs, sizeof(recv_own_msgs));
+
+ 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
+
+ CAN FD support in CAN_RAW sockets can be enabled with a new socket option
+ CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
+ not supported by the CAN_RAW socket (e.g. on older kernels), switching the
+ CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
+
+ Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
+ and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
+ when reading from the socket.
+
+ CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed
+ CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
+
+ Example:
+ [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
+
+ struct canfd_frame cfd;
+
+ nbytes = read(s, &cfd, CANFD_MTU);
+
+ if (nbytes == CANFD_MTU) {
+ printf("got CAN FD frame with length %d\n", cfd.len);
+ /* cfd.flags contains valid data */
+ } else if (nbytes == CAN_MTU) {
+ printf("got legacy CAN frame with length %d\n", cfd.len);
+ /* cfd.flags is undefined */
+ } else {
+ fprintf(stderr, "read: invalid CAN(FD) frame\n");
+ return 1;
+ }
+
+ /* the content can be handled independently from the received MTU size */
+
+ printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
+ for (i = 0; i < cfd.len; i++)
+ printf("%02X ", cfd.data[i]);
+
+ When reading with size CANFD_MTU only returns CAN_MTU bytes that have
+ been received from the socket a legacy CAN frame has been read into the
+ provided CAN FD structure. Note that the canfd_frame.flags data field is
+ not specified in the struct can_frame and therefore it is only valid in
+ CANFD_MTU sized CAN FD frames.
+
+ As long as the payload length is <=8 the received CAN frames from CAN FD
+ capable CAN devices can be received and read by legacy sockets too. When
+ user-generated CAN FD frames have a payload length <=8 these can be send
+ by legacy CAN network interfaces too. Sending CAN FD frames with payload
+ length > 8 to a legacy CAN network interface returns an -EMSGSIZE error.
+
+ Implementation hint for new CAN applications:
+
+ To build a CAN FD aware application use struct canfd_frame as basic CAN
+ data structure for CAN_RAW based applications. When the application is
+ executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
+ socket option returns an error: No problem. You'll get legacy CAN frames
+ or CAN FD frames and can process them the same way.
+
+ When sending to CAN devices make sure that the device is capable to handle
+ CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
+ The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
+
+ 4.1.6 RAW socket returned message flags
+
+ When using recvmsg() call, the msg->msg_flags may contain following flags:
+
+ MSG_DONTROUTE: set when the received frame was created on the local host.
+
+ MSG_CONFIRM: set when the frame was sent via the socket it is received on.
+ This flag can be interpreted as a 'transmission confirmation' when the
+ CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
+ In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
+
+ 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
+ 4.3 connected transport protocols (SOCK_SEQPACKET)
+ 4.4 unconnected transport protocols (SOCK_DGRAM)
+
+
+5. Socket CAN core module
+-------------------------
+
+ The Socket CAN core module implements the protocol family
+ PF_CAN. CAN protocol modules are loaded by the core module at
+ runtime. The core module provides an interface for CAN protocol
+ modules to subscribe needed CAN IDs (see chapter 3.1).
+
+ 5.1 can.ko module params
+
+ - stats_timer: To calculate the Socket CAN core statistics
+ (e.g. current/maximum frames per second) this 1 second timer is
+ invoked at can.ko module start time by default. This timer can be
+ disabled by using stattimer=0 on the module commandline.
+
+ - debug: (removed since SocketCAN SVN r546)
+
+ 5.2 procfs content
+
+ As described in chapter 3.1 the Socket CAN core uses several filter
+ lists to deliver received CAN frames to CAN protocol modules. These
+ receive lists, their filters and the count of filter matches can be
+ checked in the appropriate receive list. All entries contain the
+ device and a protocol module identifier:
+
+ foo@bar:~$ cat /proc/net/can/rcvlist_all
+
+ receive list 'rx_all':
+ (vcan3: no entry)
+ (vcan2: no entry)
+ (vcan1: no entry)
+ device can_id can_mask function userdata matches ident
+ vcan0 000 00000000 f88e6370 f6c6f400 0 raw
+ (any: no entry)
+
+ In this example an application requests any CAN traffic from vcan0.
+
+ rcvlist_all - list for unfiltered entries (no filter operations)
+ rcvlist_eff - list for single extended frame (EFF) entries
+ rcvlist_err - list for error message frames masks
+ rcvlist_fil - list for mask/value filters
+ rcvlist_inv - list for mask/value filters (inverse semantic)
+ rcvlist_sff - list for single standard frame (SFF) entries
+
+ Additional procfs files in /proc/net/can
+
+ stats - Socket CAN core statistics (rx/tx frames, match ratios, ...)
+ reset_stats - manual statistic reset
+ version - prints the Socket CAN core version and the ABI version
+
+ 5.3 writing own CAN protocol modules
+
+ To implement a new protocol in the protocol family PF_CAN a new
+ protocol has to be defined in include/linux/can.h .
+ The prototypes and definitions to use the Socket CAN core can be
+ accessed by including include/linux/can/core.h .
+ In addition to functions that register the CAN protocol and the
+ CAN device notifier chain there are functions to subscribe CAN
+ frames received by CAN interfaces and to send CAN frames:
+
+ can_rx_register - subscribe CAN frames from a specific interface
+ can_rx_unregister - unsubscribe CAN frames from a specific interface
+ can_send - transmit a CAN frame (optional with local loopback)
+
+ For details see the kerneldoc documentation in net/can/af_can.c or
+ the source code of net/can/raw.c or net/can/bcm.c .
+
+6. CAN network drivers
+----------------------
+
+ Writing a CAN network device driver is much easier than writing a
+ CAN character device driver. Similar to other known network device
+ drivers you mainly have to deal with:
+
+ - TX: Put the CAN frame from the socket buffer to the CAN controller.
+ - RX: Put the CAN frame from the CAN controller to the socket buffer.
+
+ See e.g. at Documentation/networking/netdevices.txt . The differences
+ for writing CAN network device driver are described below:
+
+ 6.1 general settings
+
+ dev->type = ARPHRD_CAN; /* the netdevice hardware type */
+ dev->flags = IFF_NOARP; /* CAN has no arp */
+
+ dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
+
+ or alternative, when the controller supports CAN with flexible data rate:
+ dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
+
+ The struct can_frame or struct canfd_frame is the payload of each socket
+ buffer (skbuff) in the protocol family PF_CAN.
+
+ 6.2 local loopback of sent frames
+
+ As described in chapter 3.2 the CAN network device driver should
+ support a local loopback functionality similar to the local echo
+ e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
+ set to prevent the PF_CAN core from locally echoing sent frames
+ (aka loopback) as fallback solution:
+
+ dev->flags = (IFF_NOARP | IFF_ECHO);
+
+ 6.3 CAN controller hardware filters
+
+ To reduce the interrupt load on deep embedded systems some CAN
+ controllers support the filtering of CAN IDs or ranges of CAN IDs.
+ These hardware filter capabilities vary from controller to
+ controller and have to be identified as not feasible in a multi-user
+ networking approach. The use of the very controller specific
+ hardware filters could make sense in a very dedicated use-case, as a
+ filter on driver level would affect all users in the multi-user
+ system. The high efficient filter sets inside the PF_CAN core allow
+ to set different multiple filters for each socket separately.
+ Therefore the use of hardware filters goes to the category 'handmade
+ tuning on deep embedded systems'. The author is running a MPC603e
+ @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
+ load without any problems ...
+
+ 6.4 The virtual CAN driver (vcan)
+
+ Similar to the network loopback devices, vcan offers a virtual local
+ CAN interface. A full qualified address on CAN consists of
+
+ - a unique CAN Identifier (CAN ID)
+ - the CAN bus this CAN ID is transmitted on (e.g. can0)
+
+ so in common use cases more than one virtual CAN interface is needed.
+
+ The virtual CAN interfaces allow the transmission and reception of CAN
+ frames without real CAN controller hardware. Virtual CAN network
+ devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
+ When compiled as a module the virtual CAN driver module is called vcan.ko
+
+ Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
+ netlink interface to create vcan network devices. The creation and
+ removal of vcan network devices can be managed with the ip(8) tool:
+
+ - Create a virtual CAN network interface:
+ $ ip link add type vcan
+
+ - Create a virtual CAN network interface with a specific name 'vcan42':
+ $ ip link add dev vcan42 type vcan
+
+ - Remove a (virtual CAN) network interface 'vcan42':
+ $ 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 available 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 message 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 message frame (see
+ also chapter 3.4).
+
+ 6.6 CAN FD (flexible data rate) driver support
+
+ CAN FD capable CAN controllers support two different bitrates for the
+ arbitration phase and the payload phase of the CAN FD frame. Therefore a
+ second bittiming has to be specified in order to enable the CAN FD bitrate.
+
+ Additionally CAN FD capable CAN controllers support up to 64 bytes of
+ payload. The representation of this length in can_frame.can_dlc and
+ canfd_frame.len for userspace applications and inside the Linux network
+ layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
+ The data length code was a 1:1 mapping to the payload length in the legacy
+ CAN frames anyway. The payload length to the bus-relevant DLC mapping is
+ only performed inside the CAN drivers, preferably with the helper
+ functions can_dlc2len() and can_len2dlc().
+
+ The CAN netdevice driver capabilities can be distinguished by the network
+ devices maximum transfer unit (MTU):
+
+ MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device
+ MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
+
+ The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
+ N.B. CAN FD capable devices can also handle and send legacy CAN frames.
+
+ FIXME: Add details about the CAN FD controller configuration when available.
+
+ 6.7 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, 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,
+ 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)
+ 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)