Subscriber failed Deserialization Error : Rosserial

asked 2020-01-31 00:11:38 -0500

alam121 gravatar image

updated 2020-01-31 02:20:20 -0500

gvdhoorn gravatar image

HI, I'm trying to create a subscriber but I'm getting the following error

rosrun rosserial_python /dev/ttyACM0
[INFO] [1580450261.541002]: ROS Serial Python Node
[INFO] [1580450261.554769]: Connecting to /dev/ttyACM0 at 57600 baud
[INFO] [1580450263.710550]: Note: publish buffer size is 280 bytes
[INFO] [1580450263.711406]: Setup publisher on my_topic [dbw_mkz_msgs/SteeringCmd]
[INFO] [1580450263.720098]: Note: subscribe buffer size is 280 bytes
[INFO] [1580450263.721023]: Setup subscriber on /vehicle/steering_cmd [dbw_mkz_msgs/SteeringCmd]
Traceback (most recent call last):
  File "/opt/ros/kinetic/lib/rosserial_python/", line 89, in <module>
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosserial_python/", line 504, in run
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosserial_python/", line 107, in handlePacket
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/dbw_mkz_msgs/msg/", line 133, in deserialize
    raise genpy.DeserializationError(e) #most likely buffer underfill
genpy.message.DeserializationError: unpack requires a string argument of length 18

The code im using is as follows

#include <ros.h>
#include <dbw_mkz_msgs/SteeringCmd.h>
#include <std_msgs/Float64.h>
#include <std_msgs/Float32.h>

float t;

ros::NodeHandle nh;

dbw_mkz_msgs::SteeringCmd msg;

void messageCb(const dbw_mkz_msgs::SteeringCmd& msg1)
    msg.count = msg1.count;
    digitalWrite(13, HIGH - digitalRead(13));

ros::Subscriber<dbw_mkz_msgs::SteeringCmd> sub("/vehicle/steering_cmd", &messageCb);

ros::Publisher p("my_topic", &msg);

void setup()

    pinMode(13, OUTPUT);


void loop()
    t = msg.count;

Any idea on what i'm doing wrong here?

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Just as in #q341697, you appear to have a very short delay(1). Would be worth checking whether increasing that helps.

gvdhoorn gravatar image gvdhoorn  ( 2020-01-31 02:21:24 -0500 )edit

Naah didn't work. It is not setting up the subscriber.

alam121 gravatar image alam121  ( 2020-02-02 01:10:25 -0500 )edit

Try removing the Serial.begin statement as that is setting the Serial speed to 115200; but your terminal output from your serial_node says it is reading data at 57600. A mismatch in speed will mean it cannot decode the data correctly.

nickw gravatar image nickw  ( 2020-02-05 00:48:11 -0500 )edit

That was my inital guess as well. However no it didn't work.

alam121 gravatar image alam121  ( 2020-02-05 01:16:17 -0500 )edit

Regardless of whether it fixed your issue: it needs to go, as what @nickw writes is true. It will never work this way.

gvdhoorn gravatar image gvdhoorn  ( 2020-02-05 02:35:45 -0500 )edit

The next thing I would try would be to change

float t;


float t=0.0;

as you are using t to set one of the fields in msg in the main loop and then publishing the message, but t will not be initialised to a known value until you receive a message on the topic you subscribe to.

nickw gravatar image nickw  ( 2020-02-05 03:22:41 -0500 )edit