UM0851 datasheet(107/245 Pages) STMICROELECTRONICS

107 / 245 page

UM0851

Communication device drivers

Doc ID 16604 Rev 2

107/245

Figure 28.

Socket-CAN architecture

4.9.3

Socket-CAN framework in Linux

The socket-CAN framework is an implementation of CAN protocol (controller area network)

which uses Berkeley socket API.

Socket-CAN implements a new protocol family (PF_CAN), which provides a socket interface

to user space applications and builds upon the Linux network layer.

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 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.

Multiple sockets can be opened at the same time, on the same or different protocol modules

and they can listen/send frames on the same or different 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, for example ISO-

TP, has just to select this protocol when opening the socket, and then it can read and write

application data byte streams, without having to deal with CAN-IDs, frames, etc.

The basic CAN frame structure and the sockaddr structures are defined in

“include/linux/can.h”:

/* CAN Frame */

struct can_frame {

canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */

__u8

can_dlc; /* data length code: 0 .. 8 */

__u8

data[8] __attribute__((aligned(8)));

};

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