https://github.com/kurt-vd/test-can-j1939

Readme + howto for can-j1939
https://github.com/kurt-vd/test-can-j1939

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Readme + howto for can-j1939

• Host: GitHub
• URL: https://github.com/kurt-vd/test-can-j1939
• Owner: kurt-vd
• License: gpl-3.0
• Created: 2015-12-11T03:09:40.000Z (almost 9 years ago)
• Default Branch: master
• Last Pushed: 2018-01-17T15:53:04.000Z (almost 7 years ago)
• Last Synced: 2024-04-18T19:34:01.390Z (7 months ago)
• Language: C
• Size: 40 KB
• Stars: 38
• Watchers: 15
• Forks: 26
• Open Issues: 1
• Metadata Files:
  • Readme: Readme.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-canbus - test-can-j1939 - How to use CAN J1939 on linux. (Protocols / J1939 Tools)

README

        
# CAN-J1939 on linux

The [Kickstart guide is here](can-j1939-kickstart.md)

## CAN on linux

See [Wikipedia:socketcan](http://en.wikipedia.org/wiki/Socketcan)

## J1939 networking in short

* Add addressing on top of CAN (destination address & broadcast)

* Any (max 1780) length packets.

  Packets of 9 or more use **Transport Protocol** (fragmentation)

  Such packets use different CANid for the same PGN.

* only **29**bit, non-**RTR** CAN frames

* CAN id is composed of

  * 0..8: SA (source address)

  * 9..26:

    * PDU1: PGN+DA (destionation address)

    * PDU2: PGN

  * 27..29: PRIO

* SA / DA may be dynamically assigned via j1939-81  

  Fixed rules of precedence in Specification, no master necessary

## J1939 on SocketCAN

J1939 is *just another protocol* that fits

in the Berkely sockets.

	socket(AF_CAN, SOCK_DGRAM, CAN_J1939)

## differences from CAN_RAW

### addressing

SA, DA & PGN are used, not CAN id.

Berkeley socket API is used to communicate these to userspace:

  * SA+PGN is put in sockname ([getsockname](http://man7.org/linux/man-pages/man2/getsockname.2.html))

  * DA+PGN is put in peername ([getpeername](http://man7.org/linux/man-pages/man2/getpeername.2.html))  

    PGN is put in both structs

PRIO is a datalink property, and irrelevant for interpretation

Therefore, PRIO is not in *sockname* or *peername*.

The *data* that is [recv][recvfrom] or [send][sendto] is the real payload.

Unlike CAN_RAW, where addressing info is data.

### Packet size

J1939 handles packets of 8+ bytes with **Transport Protocol** fragmentation transparently.

No fixed data size is necessary.

	send(sock, data, 8, 0);

will emit a single CAN frame.

	send(sock, data, 9, 0);

will use fragementation, emitting 1+ CAN frames.

## Enable j1939 (obsolete!)

CAN has no protocol id field.

The can-j1939 stack only activates when a socket opens

for a network device.

The methods described here existed in earlier implementations.

### netlink

	ip link set can0 j1939 on

This method is obsoleted in favor of _on socket connect_.

### procfs for legacy kernel (2.6.25)

This API is dropped for kernels with netlink support!

	echo can0 > /proc/net/can-j1939/net

# Using J1939

## BSD socket implementation

* socket

* bind / connect

* recvfrom / sendto

* getsockname / getpeername

## Modified *struct sockaddr_can*

	struct sockaddr_can {

		sa_family_t can_family;

		int         can_ifindex;

		union {

			struct {

				__u64 name;

				__u32 pgn;

				__u8 addr;

			} j1939;

		} can_addr;

	}

* *can_addr.j1939.pgn* is PGN

* *can_addr.j1939.addr* & *can_addr.j1939.name*  

  determine the ECU

  * receiving address information,  

    *addr* is always set,  

    *name* is set when available.

  * When providing address information,  

    *name* != 0 indicates dynamic addressing

## iproute2 (obsolete!)

Older versions of can-j1939 used a modified iproute2

for manipulating the kernel lists of current addresses.

### Static addressing

	ip addr add j1939 0x80 dev can0

### Dynamic addressing

	ip addr add j1939 name 0x012345678abcdef dev can0