In NSCLDAQ, the standard way to set up the event builder is to use the ReadoutGUI. At the moment, the ReadoutGUI provides support for the event builder through the ReadoutCallouts.tcl script. You can learn more about this script in the ReadoutGUI section of the manual, but for this situation you only need to know that it is a Tcl script that is sourced by the ReadoutGUI when starting up. We can use it to enable the event builder and configure it for use. The recommended method for setting this up is to use the event builder callout bundle. Doing so reduces the amount of Tcl that needs to be added and ensures that the event builder recovers properly from errors. Simply add the following few lines to your ReadoutCallouts.tcl script:
package require evbcallouts
::EVBC::useEventBuilder
proc OnStart {} {
::EVBC::initialize i-restart false -glombuild true -glomdt 123 -destring evbout
}
When the "Start" button is pushed in the ReadoutGUI, this will add a set of controls for the event builder to the bottom of it. The option values provided here specify that the event builder will not restart on each new run (-restart), event correlation will be enabled (-glombuild), events within 123 clock ticks of each other will be correlated (-glomdt), and the output will be put into the ring named evbout on localhost. If you prefer to change any of these parameters, feel free to do so. You can read more details about the callouts in the developer documentation as well in the man pages.
The next thing that you need to do register clients to the event builder, more specifically the event orderer. Assuming that the data being committed to the event builder are ring items, the client will be the ringFragmentSource. There is a convenience API call provided to assist in registering the ringFragmentSource called EVBC::registerRingSource. We will make use of it. However first a timestamp extractor librrary must be created for the ringFragmentSource. This library contains a function that will define how to extract a timestamp from the body of a PHYSICS_EVENT item. You can find an example of how to create one at the ringFragmentSource documentation.
The registerRingSource proc has the form:
::EVBC::registerRingSource sourceURI tstamplib id info
where sourceURI is the full URI specifying the ring buffer to read data from, tstamplib is the path to the compiled timestamp extractor library, id is the source id for the data, and info is a string that describes To illustrate how this works, consider an experiment in which the data produced by some silicon detectors are read out by a single Readout program in the system. The outputted data from this Readout are put into the "sidet0" ring buffer on localhost, and a timestamp can be properly extracted from each datum by the timestamp function recently compiled into the libtstamp.so shared library. Being the first client registered, we choose to label this stream of data with source id 0. We also want to associate a human readable description of ?Si Dets? with it. In this scenario, the line that would be added to the ReadoutCallouts.tcl would be
::EVBC::registerRingSource tcp://localhost/sidet0 /path/to/libtstamp.so 0 "Si Dets"
Putting this all together you would have a ReadoutCallouts.tcl that looks like this:
package require evbcallouts
::EVBC::useEventBuilder
proc OnStart {} {
::EVBC::initialize -restart false -glombuild true -glomdt 123
}
EVBC::registerRingSource tcp://localhost/sidet0 /path/to/libtstamp.so 0 "Si Dets"
Be aware that you need to add a registerRingSource line for every client that will be submitting data to the event builder.