How to detect and identify CANopen nodes

So you’ve got a CAN bus with some devices, but you don’t know which of them speaks “CANopen”, if any? The OVMS v3 will help you to detect them and open their CANs ;)

Before you begin

…you need to activate the CAN bus(es) you’re going to use. As a CANopen master needs to write to the network, you need to start the interfaces in active mode, i.e. …:

OVMS# can can1 start active 500000
OVMS# can can2 start active 125000

… and then start the CANopen master for the bus(es), i.e.:

OVMS# copen can1 start
OVMS# copen can2 start

Detecting CANopen nodes

The “open” in “CANopen” means any implementation can decide how much of the standard it implements. There are some few mandatory features though, a CANopen slave has to implement, if it wants to comply with the standard.

The mandatory features helping to detect and identify CANopen nodes on a CAN bus are:

  • NMT (network management), especially RESET and PREOP

  • NMT bootup event messages

  • Standard SDO access in pre-operational mode

If you’ve got CANopen nodes on a bus, even silent ones, issuing copen … nmt reset will tell all of them to reboot, and as bootup messages are mandatory, you will see them in the OVMS log output like this:

I (162904) canopen: can1 node 1 new state: Booting

The OVMS CANopen master continously monitors the network for NMT and EMCY messages. After bootup of all nodes, you can get a list of all nodes that have been detected by issuing metrics list co.:

OVMS# metrics list co.
co.can1.nd1.emcy.code
co.can1.nd1.emcy.type
co.can1.nd1.state                        Operational

Note

if you request a reset, nodes may decide to boot into pre-operational state. That may produce some error messages. Don’t worry, you can resolve this anytime by issuing copen … nmt start.

Identifying CANopen nodes

In pre-operational state, a CANopen node must be accessible at the CANopen default IDs. That means if the node supports SDO access, we can query some standard attributes from it.

That’s what copen … info and copen … scan do:

  • copen … info queries the standard device attributes from a specific node,

  • copen … scan queries all 127 node IDs.

Caution

There may be non-CANopen devices on the bus producing regular data frames at CANopen response IDs and/or reading and possibly misinterpreting CANopen requests sent to node IDs not planned by the manufacturer. Chances are low this triggers problems, but you should be ready to switch off the vehicle when doing a scan – just in case.

A complete scan takes about 20 seconds. A typical scan could look like this:

OVMS# level debug canopen
OVMS# copen can1 scan
Scan #1-127...
Node #1:
  Device type: 0x00000000
  Error state: 0x00
  Vendor ID: 0x0000001e
  Product: 0x0712302d
  Revision: 0x00010019
  S/N: 0x47c5…………
  Device name: Gen4 (Renault Twizy)11 November 2011 12
  HW version: 0x00000003
  SW version: 0712.0001
Node #23: SDO access failed
Node #25: SDO access failed
Node #27: SDO access failed
Node #30: SDO access failed
Node #87: SDO access failed
Done.
D (227994) canopen: ReadSDO #23 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
D (228194) canopen: ReadSDO #25 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
D (228444) canopen: ReadSDO #27 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
D (228844) canopen: ReadSDO #30 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
D (238384) canopen: ReadSDO #87 0x1000.00: InitUpload failed, CANopen error code 0xffffffff

This means one CANopen node was found, and some non-CANopen frames were received on IDs 0x580 +23, +25, +27, +30 and +87.

Great! What now?

As you now know there’s a CANopen node, you can look for documentation on it. You can also try to access more default SDOs to see if you can control and configure the node.

  • If you’re lucky, the device will provide its own EDS file at SDO 1021.00. You can check that by issuing…:

    OVMS# copen <bus> readsdo <nodeid> 1021 0

  • Check out the CiA specifications, for CANopen standards, for example…

    • DS301 for details on general standard SDOs

    • DS401 for the generic I/O device class definition

    • DS402 for motor controller SDOs

  • Look up the manufacturer of your device by it’s vendor ID:

  • Contact the manufacturer of your device for specific documentation and EDS files.