ReceivedDataStructure - can't seem to figure out how to make it work

[mjs513]

@fabolhak
I changed the subscriber sketch to print the message out using ReceivedDataStructure as in the example on the Subscriber tutorial on the UAVcan website. While I got the subscriber started and the sketch runs I can't seem to get the message read an printed using ReceivedDataStructure: here is new subscriber I am using:

#ifndef	SUBSCRIBER_HPP
#define	SUBSCRIBER_HPP

#include <uavcan/uavcan.hpp>
#include <uavcan/dsdlc/equipment/gnss/Fix.hpp>
#include <uavcan/helpers/ostream.hpp>

using namespace uavcan;
using namespace equipment;
using namespace gnss;



void initSubscriber(Node<NodeMemoryPoolSize> *node)
{
  // create a subscriber
    Subscriber<Fix> Fix_data_Subscriber(*node);

    const int res = Fix_data_Subscriber.start(
        [&](const ReceivedDataStructure<Fix>& msg)
        {
            /*
             * The message will be streamed in YAML format.
             */
            //std::cout << msg << std::endl;
            /*
             * If the standard iostreams are not available (they rarely available in embedded environments),
             * use the helper class uavcan::OStream defined in the header file <uavcan/helpers/ostream.hpp>.
             */
            OStream::instance() << msg << OStream::endl;
        });

  if(res < 0)
  {
    Serial.print("Unable to start subscriber!  ");
    Serial.println(res);
  } else {
    Serial.println("Subscriber Started");
  }
}

#endif

Any suggestions would be appreciated. I am going to keep playing with it just in case I missed something.

BTW: only spinOnce works if I try and use something in the form of const int res = node.spin(uavcan::MonotonicDuration::getInfinite()); it gives me an error code of 4.
Thanks
Mike

[pavel-kirienko]

I changed the subscriber sketch to print the message out using ReceivedDataStructure as in the example on the Subscriber tutorial on the UAVcan website.

ReceivedDataStructure<> provides some additional metadata about the data structure, such as the source node ID, the interface index, the timestamp, and so on; if you don't need that, you can print the message itself directly ([&](const Fix& msg)).

Your code doesn't work because the subscriber instance is destroyed when your initSubscriber() returns.

only spinOnce works if I try and use something in the form of const int res = node.spin(uavcan::MonotonicDuration::getInfinite()); it gives me an error code of 4.

Error code 4 means that the driver has returned an error: https://github.com/UAVCAN/libuavcan/blob/0dc5751ffd905f63096fb4d15485e1a1510635e5/libuavcan/include/uavcan/error.hpp#L28
Could be related to timeout handling.

[mjs513]

Hi Pavel
Thanks for getting back to me.

ReceivedDataStructure<> provides some additional metadata about the data structure, such as the source node ID, the interface index, the timestamp, and so on;

Read that and wanted to see if I could print it out using the ostream method that I saw in the subscriber example I was looking at: https://uavcan.org/Implementations/Libuavcan/Tutorials/3._Publishers_and_subscribers/. Running the subscriber from callback works great.

Your code doesn't work because the subscriber instance is destroyed when your initSubscriber() returns.

So if I put // create a subscriber Subscriber<Fix> Fix_data_Subscriber(*node); outside the function that should work? I will give it a try.

Could be related to timeout handling.

Will check that one out.

[pavel-kirienko]

So if I put // create a subscriber Subscriber Fix_data_Subscriber(*node); outside the function that should work? I will give it a try.

Yes, or just make it static.

[mjs513]

Ok. After a couple of tries I got it working with this layout for initSubscriber::

   static Subscriber<Fix> Fix_data_Subscriber(*node);

    const int res = Fix_data_Subscriber.start(
        [&](const ReceivedDataStructure<Fix>& msg)
        {
            /*
             * The message will be streamed in YAML format.
             */
            //std::cout << msg << std::endl;
            /*
             * If the standard iostreams are not available (they rarely available in embedded environments),
             * use the helper class uavcan::OStream defined in the header file <uavcan/helpers/ostream.hpp>.
             */
            Serial.println(msg.longitude_deg_1e8/1e8); 
            OStream::instance() << msg << OStream::endl;
        });

It does printout the longitude piece of the msg. But ostream is not printing. But I think that is a function of the Teensy compiler and printf function not implemented the way it should be.

I will work the timeout issue after I get this working.

[fabolhak]

Hey,
for debugging on embedded devices like Arduino and Teensy I typically use Serial.println(). I'm not sure if std::out or printf() also work, but I never saw that before. I guess someone tries to implement it here. But I don't really see a point in doing that. Serial.println() works pretty fine.

[fabolhak]

Since this is not really an issue related to this repository I will close it for now (you may reopen if you think it is valid here).

[mjs513]

@fabolhak
Well maybe it is an issue with the repsository - don't know. The fix was to remove the following lines of code from the phoenix_can_shield.h:

// this is important for UAVCAN to compile
extern "C"{
  int _getpid(){ return -1;}
  int _kill(int pid, int sig){ return -1; }
  int _write(){return -1;}
}

It compiles fine without it. Also had to add #define printf Serial.printf to the main sketch or in the subscriber.h file as well as deleting the code. As for the time out issue still working that one.