Uavcan Service call response request is empty except for the boolean fields

Applications & Usage LibCyphal
1

I am using uavcan to communicate between an IMX6 and stm32f4. stm32f4 has a configuration server which updates some parameters locally when a request is made from the IMX6::ros node. Here is the code from the IMX6 side of things:

void motorController::configCallback(const robotics_msgs::Config& conf)	{
	if(conf.enableControl)
	{
		uavcan::control::config::Config::Request req;
		req.enableControl = true;
		req.encoderTicksPerRev = params.maxEncoderTicks;
		req.maxRpm = params.maxrpmMotor;
		req.gearRatio = params.gearRatio;

		const int res = configClient.call(this->nParams.config_server_ID, req);
		if(res < 0)
		{
			ROS_INFO("config Client call failed\n");
		}
		else
			ROS_INFO("config call successful\n");
	}
}

on the stm32 side:

const int config_res = configServer.start([&](const uavcan::ReceivedDataStructure<uavcan::control::config::Config::Request>& req,
				uavcan::control::config::Config::Response& resp)
{
	if(req.enableControl)
	{
	  if(!paramsInited)
	   {
	      staticParams.maxRPM = req.maxRpm;
	      staticParams.gearRatio = req.gearRatio;
	      staticParams.maxEncoderTicks = req.encoderTicksPerRev;
	      paramsInited = true;
              resp.configApplied = true;
	  }
	  if(!driverInited)
	  {
	     driver.init(staticParams.maxRPM,staticParams.gearRatio);
	     driverInited=true;
	     resp.configApplied = true;
	  }
	}
	else
	{
	   resp.configApplied = false;
	}	
});

	
if(config_res < 0)
{
   sys::debug(Debug_Level::Error,"Failed to start config Server\r\n");
   uavcan_thd.stop();
}

after a successful service call. The boolean fields are properly initialized but the other fields are ‘0’. I have checked it with other service calls as well by making the stm32f4 a client and IMX6 a server. Below is the uavcan message definition

bool enableControl
uavcan.control.RpmPID Pid 

uint32 encoderTicksPerRev
uint16 encoderPubHz
uint16 controlLoopHz

uint8 maxRpm
uint8 gearRatio
uint8 accLimit

uint8  MODE_OPENLOOP = 0
uint8  MODE_CLOSEDLOOP = 1
uint8  mode

---

bool configApplied

Any suggestions on what might be wrong?

2

My understanding is that the boolean field you are referring to is enableControl? I see no other boolean fields in the request schema.

You seem to be using the free store (heap) in your STM32 code indirectly through the lambda closure. Probably a bad idea unless you really understand how it works and what the trade-offs are. You also seem to be running a multi-threaded environment (judging by uavcan_thd.stop()) which makes it a minefield unless the proper precautions have been taken – I assume they weren’t because you didn’t mention that.

I suggest making sure that the firmware is sound before proceeding further.

3

Hi Pavel,

Thank you for the thorough response.

In regards to the usage of free store in the code sample pasted above. I always thought of c++ lambda closures as stack-allocated objects and if i’m capturing something by reference “staticParams” here then it is simply a reference member variable of the lambda object. And the lambda lives as long as the scope in which it was declared i.e uavcan_thd::main(). Since staticParams is a member variable of the class uavcan_thd it has a longer lifetime than that of the closure. I’ve cross-checked and the closure seems to be static allocated on the uavcan_thd stack. Regarding multi-threading, currently i have disabled all other threads except the uavcan node and the chibios idle thread.

reference : https://stackoverflow.com/questions/12202656/c11-lambda-implementation-and-memory-model

4

This is the output when i query the “uavcan_data_type”::Request object in gdb:

(const uavcan::ReceivedDataStructure<uavcan::control::config::Config_::Request_<0> > &) @0x2000c9b0: {<uavcan::control::config::Config_::Request_<0>> = {static MODE_OPENLOOP = <optimized out>,
    static MODE_CLOSEDLOOP = <optimized out>, enableControl = true, Pid = {kp = 0, ki = 0, kd = 0, ilimit = 0}, encoderTicksPerRev = 0, encoderPubHz = 0, controlLoopHz = 0, maxRpm = 0 '\000', gearRatio = 0 '\000', accLimit = 0 '\000',
    mode = 0 '\000'}, <uavcan::Noncopyable> = {<No data fields>}, _transfer_ = 0x2000ca08 <can::imuNode+6024>}

only the boolean variable has been initialized to its intended value

5

Re lambdas: a heap allocation may occur when your closure is passed into start(std::function<...>) of the server. At least GCC v7 with C++14 seems to be doing that at least occasionally; the standard does not prohibit that. I would recommend to avoid closures completely unless you can tolerate dynamic storage allocation.

I don’t know why your object is not being assigned correctly, sorry. The available context is insufficient and I don’t think it is related to Libuavcan anyway.

6

Thank you @pavel.kirienko. I will remove all the lambda’s and check if the problem persists.