107 lines
3.7 KiB
Groff
107 lines
3.7 KiB
Groff
.\" $NetBSD: can.4,v 1.3 2017/05/29 08:41:57 wiz Exp $
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.\"
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.\" Copyright (c) 2017 Manuel Bouyer.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd May 18, 2017
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.Dt CAN 4
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.Os
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.Sh NAME
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.Nm CAN
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.Nd CAN Protocol
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.Sh SYNOPSIS
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.In sys/socket.h
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.In netcan/can.h
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.Ft int
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.Fn socket AF_CAN SOCK_RAW CAN_RAW
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.Sh DESCRIPTION
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.Nm
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is the network layer protocol used on top of CAN bus networks.
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At this time only the
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.Dv SOCK_RAW
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socket type is supported.
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This protocol layer is intended to be compatible with the Linux SocketCAN implementation.
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.Ss ADDRESSING
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A CAN frame consists of a 11 bits (standard frame format) or 29 bits
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(extended frame format) identifier, followed by up to 8 data bytes.
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The interpretation of the identifier is application-dependent, the CAN
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standard itself doesn't define an addressing.
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.Pp
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The
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.Nm
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layer uses a 32bits identifier.
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The 3 upper bits are used as control flags.
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The extended frame format is selected by setting the
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.Dv CAN_EFF_FLAG
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control bit.
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.Pp
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The socket address is defined as
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.Bd -literal
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struct sockaddr_can {
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u_int8_t can_len;
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sa_family_t can_family;
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int can_ifindex;
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union {
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/* transport protocol class address information */
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struct { canid_t rx_id, tx_id; } tp;
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/* reserved for future CAN protocols address information */
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} can_addr;
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};
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.Ed
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For CAN raw sockets, the 32bits identifier is part of the message data.
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The can_addr field of the sockaddr structure is not used.
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.Ss MESSAGE
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Raw CAN sockets use fixed-length messages defined as follow:
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.Bd -literal
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struct can_frame {
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canid_t can_id; /* ID + EFF/RTR/ERR flags */
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uint8_t can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */
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uint8_t __pad;
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uint8_t __res0;
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uint8_t __res1;
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uint8_t data[CAN_MAX_DLEN] __aligned(8);
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};
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.Ed
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The lower 11 bits (for standard frames) or 29 bits (for extended frames) are
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used as the on-wire identifier.
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The
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.Dv CAN_EFF_FLAG
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bit is set in can_id for extended frames.
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The
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.Dv CAN_RTR_FLAG
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bit is set in can_id for remote transmission request frames.
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.Sh SEE ALSO
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.Xr socket 2 ,
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.Xr canloop 4 ,
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.Xr netintro 4 ,
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.Xr canconfig 8 ,
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.Pa /usr/include/netcan/can.h
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.Pp
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.Lk https://en.wikipedia.org/wiki/SocketCAN "SocketCAN - Wikipedia"
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.Lk https://www.kernel.org/doc/Documentation/networking/can.txt "Readme file for the Controller Area Network Protocol Family"
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.Sh HISTORY
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The
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.Nm
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protocol appeared in
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.Nx 8.0 .
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.Sh BUGS
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.Dv CANFD
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and error frames are not implemented.
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