203 lines
4.3 KiB
Markdown
203 lines
4.3 KiB
Markdown
# Kickstart guide to can-j1939 on linux
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## Prepare using VCAN
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You may skip this step entirely if you have a functional
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**can0** bus on your system.
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Load module, when *vcan* is not in-kernel
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modprobe vcan
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Create a virtual can0 device and start the device
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ip link add can0 type vcan
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ip link set can0 up
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## First steps with j1939
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Use [testj1939](testj1939.c)
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When *can-j1939* is compiled as module, opening a socket will load it,
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__or__ you can load it manually
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modprobe can-j1939
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Most of the subsequent examples will use 2 sockets programs (in 2 terminals).
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One will use CAN_J1939 sockets using *testj1939*,
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and the other will use CAN_RAW sockets using cansend+candump.
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testj1939 can be told to print the used API calls by adding **-v** program argument.
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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 and *testj1939* does not receive it.
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### Use source address
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Binding a can-j1939 socket to a source address will register
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allow you to send packets.
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./testj1939 can0:0x80
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Your system had, for a small moment, source address 0x80 assigned.
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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 can0:0x80,0x3ffff
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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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./testj1939 -s can0:0x90,0x3ffff
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produces **1BFFFF90#0123456789ABCDEF** ,
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### Use PDU1 PGN
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./testj1939 -s can0:0x80,0x12345
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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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### Use destination address info
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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 can0:0x80,0x12345 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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For broadcasted transmissions
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./testj1939 -s can0:0x80,0x12300 :,0x32100
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emits **1B21FF80#0123456789ABCDEF** rather than 1923FF80#012345678ABCDEF
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Desitination specific transmissions
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./testj1939 -s can0:0x80,0x12300 :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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First assign 0x90 to the local system.
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This becomes important because the kernel must interact in the
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transport protocol sessions before the complete packet is delivered.
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./testj1939 can0:0x90 -r &
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Now test:
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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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### advanced filtering
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## dynamic addressing
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