CAN(4)

CAN(4) | Device Drivers Manual | CAN(4)

# NAME

`CAN` —
CAN Protocol

# SYNOPSIS

`#include <sys/socket.h>`
`#include <netcan/can.h>`

int
`socket`(AF_CAN, SOCK_RAW, CAN_RAW);

# DESCRIPTION

`CAN` is the network layer protocol used on top of CAN bus networks. At this time only the `SOCK_RAW` socket type is supported. This protocol layer is intended to be compatible with the Linux SocketCAN implementation.

## ADDRESSING

A CAN frame consists of a 11 bits (standard frame format) or 29 bits (extended frame format) identifier, followed by up to 8 data bytes. The interpretation of the identifier is application-dependent, the CAN standard itself doesn't define an addressing.

The `CAN` layer uses a 32bits identifier. The 3 upper bits are used as control flags. The extended frame format is selected by setting the `CAN_EFF_FLAG` control bit.

The socket address is defined as

    struct sockaddr_can {
            u_int8_t        can_len;
            sa_family_t     can_family;
            int             can_ifindex;
            union {
                    /* transport protocol class address information */
                    struct { canid_t rx_id, tx_id; } tp;
                    /* reserved for future CAN protocols address information */
            } can_addr;
    };

For CAN raw sockets, the 32bits identifier is part of the message data. The can_addr field of the sockaddr structure is not used.

## MESSAGE

Raw CAN sockets use fixed-length messages defined as follow:

    struct can_frame {
            canid_t can_id; /* ID + EFF/RTR/ERR flags */
            uint8_t can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */
            uint8_t __pad;
            uint8_t __res0;
            uint8_t __res1;
            uint8_t data[CAN_MAX_DLEN] __aligned(8);
    };

The lower 11 bits (for standard frames) or 29 bits (for extended frames) are used as the on-wire identifier. The `CAN_EFF_FLAG` bit is set in can_id for extended frames. The `CAN_RTR_FLAG` bit is set in can_id for remote transmission request frames.

# SEE ALSO

socket(2), canloop(4), netintro(4), canconfig(8), /usr/include/netcan/can.h

SocketCAN - Wikipedia Readme file for the Controller Area Network Protocol Family

# HISTORY

The `CAN` protocol appeared in NetBSD 8.0.

# BUGS

`CANFD` and error frames are not implemented.

May 18, 2017 | NetBSD 9.5