Use simulated time with some nodes while running other nodes with wall time

edit

Hi

I am trying to run some nodes with simulated time while running other nodes with wall time (same rosmaster). I used the following launch configuration.

<launch>
<param name="pi/use_sim_time" value="true" />
<node name="talker" pkg="demo1" type="talker" />
<node name="listerner" pkg="demo1"  type="listener" ns="pi"  /> 
</launch>

My expectation was listerner should use simulated time and talker should use wall time. But neither of them do so. It seems all ros nodes are using the global parameter "use_sim_time" to change the timing mode. Are there any other way to do this?

Edit:

I run master node in my computer and various other nodes in different raspberry Pis and other computers. I need to synchronize the time of all nodes to my computers time to measure the processing and transmission delays of nodes. NTP is not a good option here.

1. My Pis does not have access to Internet or any other common network.
2. I think it is really expensive to setup and maintain my own NTP server in my computer
3. I do not like to touch the system time of other computers.