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Client socket interface to CANopenNode ASCII command interface

cocomm is a small command line program, which establishes socket connection with canopend (CANopen Linux commander device). It sends standardized CANopen commands (CiA309-3) to gateway and prints the responses to stdout and stderr. It is similar to command nc -U /tmp/CO_command_socket, but adjusted to CANopen.

Compile and install

cd cocomm
make
sudo make install

This will compile the cocomm utility and copy it to the /usr/bin/ directory.

Example usage

cocomm --help
cocomm "help"
cocomm "help datatype"
cocomm "help lss"
cocomm "1 read 0x1017 0 u16"
cocomm "1 write 0x1017 0 u16 1000"
cocomm "1 w 0x1010 1 vs save"
cocomm "1 reset node"

Example will display usage help, read Heartbeat producer time from CANopen device with NodeId = 1, write 1000 ms to the same variable, store all non-volatile data on the device and reset the device. (Suppose CANopen device with NodeId = 1 is our CANopen Linux commander device. After 'reset node' command, our device will be stopped and cocomm won't work any more. Of course, cocomm can access any CANopen device, just by specifying it's node ID.)

Parameters to program can be set by program arguments, as described in cocomm --help, and can also be changed by environmental variables. For example, to change default socket path for all next cocomm commands in current terminal, type:

export cocomm_socket="some other path than /tmp/CO_command_socket"

Commands can be also written into a file, for example create a commands.txt file, and for its content enter the commands:

[1] r 0x1017 0 u16
[2] 1 start

Then make cocomm use that file:

$ cocomm -f commands.txt
[1] 1000
[2] OK

Program writes data to stdout and messages in green or red color to stderr.

For more examples see CANopenDemo.

Background about communication paths, when using cocomm

  1. canopend serves a socket connection on /tmp/CO_command_socket address. This is local Unix socket, TCP socket can be used also. canopend is pure CANopen device with commander functionalities and gateway. It listens for socket connections.
  2. When run, cocomm tries to connect to /tmp/CO_command_socket address (this is default setting). canopend accepts the connection.
  3. cocomm writes the specified ascii command to established socket connection, for example [1] 4 read 0x1017 0 u16.
  4. Gateway in canopend receives the command and decodes it. read commands goes internally into CO_SDOclientUploadInitiate() and then command is processed with multiple CO_SDOclientUpload() function calls.
  5. CO_SDOclientUpload() now sends a CAN message to targeted CANopen device. (CAN interface in Linux is implemented with CAN sockets. This is the third type of sockets mentioned here.) However, in our example targeted CANopen device receives SDO request, asking the value of the variable, located in Object Dictionary at index 0x1017, subindex 0.
  6. Targeted CANopen device receives CAN message with CAN ID=0x604. It determines SDO request, so CO_SDOserver_process() function gets the message. Function gets the value from internal Object Dictionary and sends the CAN response with CAN ID=0x584. Those messages can be seen in candump terminal. And it is not necessary to understand the details of SDO communication, it may be quite complex.
  7. canopend receives the CAN message, CO_SDOclientUpload() decodes it and sends binary value to the gateway.
  8. Gateway in canopend translates binary value to asciiValue, unsigned16 in our example. It prepares the response, in our case [1] + asciiValue + \r\n. Then writes the response text back to /tmp/CO_command_socket.
  9. cocomm reads the response text from local socket and prints it partly to stderr ([1] \r\n) and partly to stdout (asciiValue).
  10. If there are more commands, step 3 is repeated. Otherwise cocomm closes the socket connection and exits.