import sample program & help page
Kurt Van Dijck
parent
fe748b1c2c
commit
198c5801ec
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OUTPUT = j1939.html testj1939
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default: $(OUTPUT)
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%.html: %.page page.theme
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theme -f -o $@ $< -p "$*"
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CFLAGS = -Wall -g3 -O0
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clean:
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rm -f $(wildcard *.o) $(OUTPUT)
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# CAN-J1939 on linux
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## CAN on linux
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See [Wikipedia:socketcan](http://en.wikipedia.org/wiki/Socketcan)
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## J1939 networking in short
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* Add addressing on top of CAN (destination address & broadcast)
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* Any (max 1780) length packets.
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Packets of 9 or more use **Transport Protocol** (fragmentation)
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Such packets use different CANid for the same PGN.
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* only **29**bit, non-**RTR** CAN frames
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* CAN id is composed of
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* 0..8: SA (source address)
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* 9..26:
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* PDU1: PGN+DA (destionation address)
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* PDU2: PGN
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* 27..29: PRIO
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* SA / DA may be dynamically assigned via j1939-81
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Fixed rules of precedence in Specification, no master necessary
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## J1939 on SocketCAN
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J1939 is *just another protocol* that fits
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in the Berkely sockets.
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socket(AF_CAN, SOCK_DGRAM, CAN_J1939)
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## differences from CAN_RAW
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### addressing
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SA, DA & PGN are used, not CAN id.
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Berkeley socket API is used to communicate these to userspace:
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* SA+PGN is put in sockname ([getsockname](http://man7.org/linux/man-pages/man2/getsockname.2.html))
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* DA+PGN is put in peername ([getpeername](http://man7.org/linux/man-pages/man2/getpeername.2.html))
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PGN is put in both structs
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PRIO is a datalink property, and irrelevant for interpretation
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Therefore, PRIO is not in *sockname* or *peername*.
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The *data* that is [recv][recvfrom] or [send][sendto] is the real payload.
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Unlike CAN_RAW, where addressing info is data.
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### Packet size
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J1939 handles packets of 8+ bytes with **Transport Protocol** fragmentation transparently.
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No fixed data size is necessary.
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send(sock, data, 8, 0);
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will emit a single CAN frame.
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send(sock, data, 9, 0);
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will use fragementation, emitting 1+ CAN frames.
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# Enable j1939
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CAN has no protocol id field.
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Enabling protocols must be done manually
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### netlink
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ip link set can0 j1939 on
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### procfs for legacy kernel (2.6.25)
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This API is dropped for kernels with netlink support!
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echo can0 > /proc/net/can-j1939/net
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# Using J1939
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## BSD socket implementation
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* socket
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* bind / connect
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* recvfrom / sendto
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* getsockname / getpeername
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## Modified *struct sockaddr_can*
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struct sockaddr_can {
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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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struct {
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__u64 name;
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__u32 pgn;
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__u8 addr;
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} j1939;
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} can_addr;
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}
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* *can_addr.j1939.pgn* is PGN
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* *can_addr.j1939.addr* & *can_addr.j1939.name*
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determine the ECU
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* receiving address information,
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*addr* is always set,
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*name* is set when available.
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* When providing address information,
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*name* != 0 indicates dynamic addressing
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## iproute2
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### Static addressing
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ip addr add j1939 0x80 dev can0
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### Dynamic addressing
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ip addr add j1939 name 0x012345678abcdef dev can0
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# First steps with j1939
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Use [testj1939](testj1939.c)
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Load modules, when vcan & can-j1939 are not in-kernel
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modprobe vcan
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modprobe can-j1939
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### create virtual CAN bus
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Make sure *can0* is available, or replace *can0* with *vcan0*
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ip link add can0 type vcan
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### enable CAN
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ip link set can0 up
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### enable j1939
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modprobe can-j1939
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### receive without source address
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Do in terminal 1
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./testj1939 -r can0:
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Send raw CAN in terminal 2
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cansend can0 1823ff40#0123
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You should have this output in terminal 1
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40 02300: 01 23
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This means, from NAME 0, SA 40, PGN 02300 was received,
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with 2 databytes, *01* & *02*.
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now emit this CAN message:
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cansend can0 18234140#0123
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In J1939, this means that ECU 0x40 sends directly to ECU 0x41
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Since we did not bind to address 0x41, this traffic
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is not meant for us.
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### Use source address
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./testj1939 can0:0x80
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will say
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./testj1939: bind(): Cannot assign requested address
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Since J1939 maintains addressing, **0x80** has not yet been assigned
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as an address on **can0** . This behaviour is very similar to IP
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addressing: you cannot bind to an address that is not your own.
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Now tell the kernel that we *own* address 0x80.
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It will be available from now on.
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ip addr add j1939 0x80 dev can0
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./testj1939 can0:0x80
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now succeeds.
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### receive with source address
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Terminal 1:
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./testj1939 -r can0:0x80
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Terminal 2:
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cansend can0 18238040#0123
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Will emit this output
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40 02300: 01 23
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This is because the traffic had destination address __0x80__ .
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### send
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Open in terminal 1:
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candump -L can0
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And to these test in another terminal
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./testj1939 -s can0:0x80
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This produces **1BFFFF80#0123456789ABCDEF** on CAN.
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### Multiple source addresses on 1 CAN device
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ip addr add j1939 0x90 dev can0
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./testj1939 -s can0:0x90
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produces **1BFFFF90#0123456789ABCDEF** ,
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./testj1939 -s can0:
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still produces **1BFFFF80#0123456789ABCDEF** , since **0x80**
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is the default _source address_.
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Check
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ip addr show can0
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emits
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X: can0: <NOARP,UP,LOWER_UP> mtu 16 qdisc noqueue state UNKNOWN
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link/can
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can-j1939 0x80 scope link
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can-j1939 0x90 scope link
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0x80 is the first address on can0.
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### Use specific PGN
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./testj1939 -s can0:,0x12345
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emits **1923FF80#0123456789ABCDEF** .
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Note that the real PGN is **0x12300**, and destination address is **0xff**.
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### Emit destination specific packets
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The destination field may be set during sendto().
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*testj1939* implements that like this
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./testj1939 -s can0:,0x12345 can0:0x40
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emits **19234080#0123456789ABCDEF** .
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The destination CAN iface __must__ always match the source CAN iface.
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Specifing one during bind is therefore sufficient.
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./testj1939 -s can0:,0x12300 :0x40
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emits the very same.
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### Emit different PGNs using the same socket
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The PGN is provided in both __bind( *sockname* )__ and
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__sendto( *peername* )__ , and only one is used.
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*peername* PGN has highest precedence.
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./testj1939 -s can0:,0x12300 :0x40,0x32100
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emits **1B214080#0123456789ABCDEF** .
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It makes sometimes sense to omit the PGN in __bind( *sockname* )__ .
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### Larger packets
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J1939 transparently switches to *Transport Protocol* when packets
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do not fit into single CAN packets.
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./testj1939 -s20 can0:0x80 :,0x12300
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emits:
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18ECFF80#20140003FF002301
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18EBFF80#010123456789ABCD
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18EBFF80#02EF0123456789AB
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18EBFF80#03CDEF01234567
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The fragments for broadcasted *Transport Protocol* are seperated
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__50ms__ from each other.
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Destination specific *Transport Protocol* applies flow control
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and may emit CAN packets much faster.
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./testj1939 -s20 can0:0x80 :0x90,0x12300
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emits:
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18EC9080#1014000303002301
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18EC8090#110301FFFF002301
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18EB9080#010123456789ABCD
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18EB9080#02EF0123456789AB
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18EB9080#03CDEF01234567
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18EC8090#13140003FF002301
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The flow control causes a bit overhead.
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This overhead scales very good for larger J1939 packets.
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# Advanced topics with j1939
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### Change priority of J1939 packets
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./testj1939 -s can0:0x80,0x0100
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./testj1939 -s -p3 can0:0x80,0x0200
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emits
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1801FF80#0123456789ABCDEF
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0C02FF80#0123456789ABCDEF
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### using connect
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## dynamic addressing
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@ -0,0 +1,21 @@
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<!DOCTYPE html>
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<html>
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<head>
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<title>page: <?theme title?></title>
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<link rel="stylesheet" type="text/css" href="style.css">
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<style>
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div#toc li {
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list-style : none;
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}
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</style>
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</head>
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<body>
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<div id='toc'>
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<?theme toc?>
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</div>
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<?theme body?>
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</div>
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</body>
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</html>
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* {
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font-family: Helvetica Neue, Helvetica, Arial, sans-serif;
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}
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body {
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max-width: 60em;
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margin: 0 auto;
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color: #111;
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}
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pre, code {
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font-family: Monaco, Courier New, monospace;
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font-size: 11px;
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}
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h1 {
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color: rgb(43,105,145);
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font-weight: bold;
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font-size: 40px;
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letter-spacing: -1px;
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margin-bottom: -5px;
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margin: 0;
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}
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h1 code {
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font-size: 32px;
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}
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h2 {
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color: rgb(43,105,145);
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font-weight: bold;
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margin-bottom: -5px;
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}
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h2 code {
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font-size: 22px;
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}
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h3 {
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margin-bottom: -5px;
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}
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h3 code {
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font-size: 16px;
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}
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a {
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color: blue;
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text-decoration: none;
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}
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a:visited {
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color: navy;
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}
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a:hover {
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text-decoration: underline;
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}
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pre {
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border-width: 1px;
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border-color: #777;
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border-style: solid;
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padding: 0.5em;
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background-color: #ccc;
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overflow: auto;
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color: #000;
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font-weight: bold;
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}
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p, li {
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font-size: 13px;
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line-height: 18px;
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}
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/*
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* Copyright (c) 2013 EIA Electronics
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*
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* Authors:
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* Kurt Van Dijck <kurt.van.dijck@eia.be>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the version 2 of the GNU General Public License
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* as published by the Free Software Foundation
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*/
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#include <signal.h>
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#include <time.h>
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#include <inttypes.h>
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#include <errno.h>
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#include <string.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <getopt.h>
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#include <error.h>
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#include <sys/time.h>
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#include <sys/socket.h>
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#include <net/if.h>
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#include <linux/can.h>
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#include <linux/can/j1939.h>
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static const char help_msg[] =
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"testj1939: demonstrate j1939 use\n"
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"Usage: testj1939 FROM TO\n"
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" FROM / TO - or [IFACE][:[SA][,[PGN][,NAME]]]\n"
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"Options:\n"
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" -s[=LEN] Initial send of LEN bytes dummy data\n"
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" -r Receive (and print) data\n"
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" -e Echo incoming packets back\n"
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" This atually receives packets\n"
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" -c Issue connect()\n"
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" -p=PRIO Set priority to PRIO\n"
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" -n Emit 64bit NAMEs in output\n"
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"\n"
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"Example:\n"
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"testj1939 can1 20\n"
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"\n"
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;
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static const char optstring[] = "?vs::rep:cn";
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static void parse_canaddr(char *spec, struct sockaddr_can *paddr)
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{
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char *str;
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str = strsep(&spec, ":");
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if (strlen(str))
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paddr->can_ifindex = if_nametoindex(str);
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str = strsep(&spec, ",");
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if (str && strlen(str))
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paddr->can_addr.j1939.addr = strtoul(str, NULL, 0);
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str = strsep(&spec, ",");
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if (str && strlen(str))
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paddr->can_addr.j1939.pgn = strtoul(str, NULL, 0);
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str = strsep(&spec, ",");
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if (str && strlen(str))
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paddr->can_addr.j1939.name = strtoul(str, NULL, 0);
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}
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/* main */
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int main(int argc, char *argv[])
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{
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int ret, sock, opt, j;
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socklen_t peernamelen;
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struct sockaddr_can sockname = {
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.can_family = AF_CAN,
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.can_addr.j1939 = {
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.addr = J1939_NO_ADDR,
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.name = J1939_NO_NAME,
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.pgn = J1939_NO_PGN,
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},
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}, peername = {
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.can_family = AF_CAN,
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.can_addr.j1939 = {
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.addr = J1939_NO_ADDR,
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.name = J1939_NO_NAME,
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.pgn = J1939_NO_PGN,
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},
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};
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uint8_t dat[128];
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int todo_send = 0, todo_recv = 0, todo_echo = 0, todo_prio = -1;
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int todo_connect = 0, todo_names = 0;
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/* argument parsing */
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while ((opt = getopt(argc, argv, optstring)) != -1)
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switch (opt) {
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case 's':
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todo_send = strtoul(optarg ?: "8", NULL, 0);
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break;
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case 'r':
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todo_recv = 1;
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break;
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case 'e':
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todo_echo = 1;
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break;
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case 'p':
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todo_prio = strtoul(optarg, NULL, 0);
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break;
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case 'c':
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todo_connect = 1;
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break;
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case 'n':
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todo_names = 1;
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break;
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default:
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fputs(help_msg, stderr);
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exit(1);
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break;
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}
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if (argv[optind]) {
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if (strcmp("-", argv[optind]))
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parse_canaddr(argv[optind], &sockname);
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++optind;
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}
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if (argv[optind]) {
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if (strcmp("-", argv[optind]))
|
||||
parse_canaddr(argv[optind], &peername);
|
||||
++optind;
|
||||
}
|
||||
|
||||
/* open socket */
|
||||
sock = ret = socket(PF_CAN, SOCK_DGRAM, CAN_J1939);
|
||||
if (ret < 0)
|
||||
error(1, errno, "socket(j1939)");
|
||||
|
||||
if (todo_prio >= 0) {
|
||||
ret = setsockopt(sock, SOL_CAN_J1939, SO_J1939_SEND_PRIO,
|
||||
&todo_prio, sizeof(todo_prio));
|
||||
if (ret < 0)
|
||||
error(1, errno, "set priority %i", todo_prio);
|
||||
}
|
||||
|
||||
ret = bind(sock, (void *)&sockname, sizeof(sockname));
|
||||
if (ret < 0)
|
||||
error(1, errno, "bind()");
|
||||
|
||||
if (todo_connect) {
|
||||
ret = connect(sock, (void *)&peername, sizeof(peername));
|
||||
if (ret < 0)
|
||||
error(1, errno, "connect()");
|
||||
}
|
||||
|
||||
if (todo_send) {
|
||||
/* initialize test vector */
|
||||
for (j = 0; j < sizeof(dat); ++j)
|
||||
dat[j] = ((2*j) << 4) + ((2*j+1) & 0xf);
|
||||
|
||||
/* send data */
|
||||
ret = sendto(sock, dat, todo_send, 0,
|
||||
(void *)&peername, sizeof(peername));
|
||||
if (ret < 0)
|
||||
error(1, errno, "sendto");
|
||||
}
|
||||
|
||||
/* main loop */
|
||||
while (todo_echo || todo_recv) {
|
||||
/*
|
||||
* re-use peername for storing the sender's peername of
|
||||
* received packets
|
||||
*/
|
||||
peernamelen = sizeof(peername);
|
||||
ret = recvfrom(sock, dat, sizeof(dat), 0,
|
||||
(void *)&peername, &peernamelen);
|
||||
if (ret < 0) {
|
||||
if (EINTR == errno)
|
||||
continue;
|
||||
error(1, errno, "recvfrom()");
|
||||
}
|
||||
|
||||
if (todo_echo) {
|
||||
ret = sendto(sock, dat, ret, 0,
|
||||
(void *)&peername, peernamelen);
|
||||
if (ret < 0)
|
||||
error(1, errno, "sendto");
|
||||
}
|
||||
if (todo_recv) {
|
||||
if (todo_names && peername.can_addr.j1939.name)
|
||||
printf("%016llx ", peername.can_addr.j1939.name);
|
||||
printf("%02x %05x:", peername.can_addr.j1939.addr,
|
||||
peername.can_addr.j1939.pgn);
|
||||
for (j = 0; j < ret; ++j)
|
||||
printf(" %02x", dat[j]);
|
||||
printf("\n");
|
||||
}
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue