How can several controllers be synchronized?

If you are not performing time resolved measurements, you will probably not need any synchronization of the controllers: they will be started sequentially by the software and their acquisition will have a jitter of a few ms.
In the case you need a precise synchronization, on the other hand, hardware connection is required between the controllers through the external IO signals. The external signals used for this synchronization should be configured as sync with the extsig command.
In this case a master controller should be defined for the acquisition which will the send the synchronization signal to the other controllers, while the other controllers will use them as inputs.
The type of synchronization can begating or trigger depending if the synchronization signal will gate the slave detectors or trigegr the beginning of the acquisition. There are no particular reasons to chose one or the other method, except if the user finds out that one is more stable than the other.
Normally the configuration of the synchronization is configured inside the configuration file and should not be changed dynamically by the user.

After the configuration, the synchronization of the controllers will be completely transparent for the user, who will simply have to setup the timing parameters of the detector as a whole.