The max_freq limit needs improvement

[Peixuan Shu]

In the config/ros_topics.yaml, the max_freq only guarantees the sending frequency is lower than that but not be that. If the send_topics frequency is larger than max_freq, the node will decrease it by 2x, 3x, ... until it satisfies the max_freq.

This is because the bridge_node will check if the time interval between two sends is larger than 1/max_freq. If it is larger, this sending message will be discarded. However, the sending freq is not stable which leads to some abnormal discardings of messages.

swarm_ros_bridge/src/bridge_node.cpp

Lines 27 to 35 in 8b4a391

 /* uniform callback functions for ROS subscribers */ 
 template <typename T, int i> 
 void sub_cb(const T &msg) 
 { 
   /* frequency control */ 
   ros::Time t_now = ros::Time::now(); 
   if ((t_now - sub_t_last[i]).toSec() * sendTopics[i].max_freq < 1.0) 
     {return;} 
   sub_t_last[i] = t_now; 

It brings problems especially when the sending frequency is near max_freq, the sending freq will decrease by about 2 times as well.

So the sending freq limiting mechanism needs improvement.

[Peixuan Shu]

This bug has been fixed by commit 45e1b07. Now the max_freq will actually limit the frequency to it as the freq_control logic controls the average sending frequency in each second.