200 lines
7.7 KiB
Plaintext
200 lines
7.7 KiB
Plaintext
================================================================================
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How to detect and identify CANopen nodes
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================================================================================
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So you've got a CAN bus with some devices, but you don't know which of them
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speaks "CANopen", if any? The OVMS v3 will help you to detect them and open
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their CANs ;)
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CANopen basics
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--------------
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A CANopen network consists of "masters" and "slaves", masters are clients,
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slaves are servers. At most one master may be active at a time.
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CANopen supports addressing of up to 127 slaves on a bus using node IDs 1-127.
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Node address 0 is used for broadcasts to all nodes.
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The CANopen protocol mainly consists of…
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- PDOs (process data objects)
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- SDOs (service data objects)
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- NMT (network management)
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- SYNC (synchronisation)
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- EMCY (emergency events)
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PDOs are regular, normally periodical, status update frames, for example sensor
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data. You can log them using "can … trace on". PDOs can be sent at any CAN ID
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except those reserved for other CANopen services.
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SDOs are memory registers of nodes that can be read and written by masters on
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request. SDO requests are normally sent at ID 0x600 + nodeid, responses at ID
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0x580 + nodeid. SDOs are addressed by a 16 bit index + 8 bit subindex. Registers
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and data types for a given device are documented by the device specific object
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dictionary, normally represented as an EDS (electronic data sheet) file.
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NMTs are short datagrams to control node startup / shutdown. There's a special
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node state "pre-operational" allowing access to all operation and communication
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parameters of a node in a standardized way. NMT requests are sent at ID 0x000,
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responses and unsolicited updates (aka heartbeats) are sent at ID 0x700 +
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nodeid with length 1.
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SYNC messages are datagrams of length 0, normally sent at ID 0x080.
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EMCY messages are only sent if a node encounters some kind of alert or warning
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condition, they are normally sent at ID 0x080 + nodeid with a length of 8 bytes.
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So if any of these IDs look familiar to you, chances are you've got a CANopen
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network.
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Note: CANopen coexists nicely with OBD-II and often does in a vehicle (i.e.
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Renault Twizy). OBD-II devices normally are addressed at IDs > 0x780 so are
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outside the CANopen ID range. Even if they use non-standard IDs, the devices
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normally will detect and ignore frames not matching their protocol.
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But of course there may be non-CANopen devices on the bus producing regular data
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frames at CANopen response IDs and/or reading and possibly misinterpreting
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CANopen requests sent to node IDs not planned by the manufacturer. Chances are
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low this triggers problems, but you should be ready to switch off the vehicle
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when doing a scan -- just in case.
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Before you begin
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----------------
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…you need to activate the CAN bus(es) you're going to use. As a CANopen master
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needs to write to the network, you need to start the interfaces in active mode,
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i.e. …
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OVMS > can can1 start active 500000
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OVMS > can can2 start active 125000
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… and then start the CANopen master for the bus(es), i.e.:
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OVMS > copen can1 start
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OVMS > copen can2 start
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Detecting CANopen nodes
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-----------------------
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The "open" in "CANopen" means any implementation can decide how much of the
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standard it implements. There are some few mandatory features though, a CANopen
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slave has to implement, if it wants to comply with the standard.
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The mandatory features helping to detect and identify CANopen nodes on a CAN
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bus are:
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- NMT (network management), especially RESET and PREOP
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- NMT bootup event messages
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- Standard SDO access in pre-operational mode
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If you've got CANopen nodes on a bus, even silent ones, issuing "copen … nmt
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reset" will tell all of them to reboot, and as bootup messages are mandatory,
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you will see them in the OVMS log output like this:
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I (162904) canopen: can1 node 1 new state: Booting
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The OVMS CANopen master continously monitors the network for NMT and EMCY
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messages. After bootup of all nodes, you can get a list of all nodes that have
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been detected by issuing "metrics list co.":
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OVMS > metrics list co.
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co.can1.nd1.emcy.code
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co.can1.nd1.emcy.type
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co.can1.nd1.state Operational
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Note: if you request a reset, nodes may decide to boot into pre-operational
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state. That may produce some error messages. Don't worry, you can resolve this
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anytime by issuing "copen … nmt start".
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Identifying CANopen nodes
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-------------------------
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In pre-operational state, a CANopen node must be accessible at the CANopen
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default IDs. That means if the node supports SDO access, we can query some
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standard attributes from it.
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That's what "copen … info" and "copen … scan" do. "copen … scan" queries all 127 node
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IDs for the SDO standard device attributes. A complete scan takes about 20
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seconds. A typical scan could look like this:
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OVMS > level debug canopen
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OVMS > copen can1 scan
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Scan #1-127...
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Node #1:
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Device type: 0x00000000
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Error state: 0x00
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Vendor ID: 0x0000001e
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Product: 0x0712302d
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Revision: 0x00010019
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S/N: 0x47c5…………
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Device name: Gen4 (Renault Twizy)11 November 2011 12
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HW version: 0x00000003
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SW version: 0712.0001
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Node #23: SDO access failed
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Node #25: SDO access failed
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Node #27: SDO access failed
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Node #30: SDO access failed
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Node #87: SDO access failed
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Done.
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D (227994) canopen: ReadSDO #23 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
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D (228194) canopen: ReadSDO #25 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
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D (228444) canopen: ReadSDO #27 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
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D (228844) canopen: ReadSDO #30 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
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D (238384) canopen: ReadSDO #87 0x1000.00: InitUpload failed, CANopen error code 0xffffffff
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This means one CANopen node was found, and some non-CANopen frames were
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received on IDs 0x580 +23, +25, +27, +30 and +87.
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Great! What now?
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----------------
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As you now know there's a CANopen node, you can look for documentation on it.
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You can also try to access more default SDOs to see if you can control and
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configure the node.
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If you're lucky, the device will provide its own EDS file at SDO 1021.00. You
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can check that by issuing…
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copen … readsdo <nodeid> 1021 0
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The SDO address space layout is standardized:
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Index (hex) Object
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0000 not used
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0001-001F Static Data Types
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0020-003F Complex Data Types
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0040-005F Manufacturer Specific Complex Data Types
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0060-007F Device Profile Specific Static Data Types
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0080-009F Device Profile Specific Complex Data Types
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00A0-0FFF Reserved for further use
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1000-1FFF Communication Profile Area
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2000-5FFF Manufacturer Specific Profile Area
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6000-9FFF Standardised Device Profile Area
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A000-BFFF Standardised Interface Profile Area
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C000-FFFF Reserved for further use
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See CiA DS301 for details on standard SDOs:
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https://www.can-cia.org/standardization/specifications/
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For example, a device shall tell about the PDOs it transmits or listens to,
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their IDs, update frequency and content structure at SDO registers 1400-1BFF.
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This is mandatory in theory but real devices may not fully comply to that rule.
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CANopen compliant standard device types like motor controllers need to
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implement some standard profile registers. See CiA DS401 for the generic I/O
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device class definition or DS402 for motor controllers.
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Most devices will require some kind of login before allowing you to change
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operational parameters. This is also done using SDO writes, but there is no
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standard for this, so you'll need to dig into the device documentation.
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Of course there's a lot more on CANopen, but this should get you going.
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Have fun!
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