9.3. The evblite Tcl package.
EVBLite is a Linux pipeline. The evblite Tcl package makes it easy to define, start and stop the EVBLite pipeline passing the evbtagger and glom programs any options required to make the function properly. The evblite package can be used in the ReadoutCallouts.tcl script to automatically start the pipeline. It is recommended that this be done in OnStart as the pipeline is persistent.
Here's a sample fragment from a ReadoutCallouts.tcl script that sets up and starts EVBLite when the system transitions from not ready to halted:
Example 9-1. Starting EVBLite from ReadoutCallouts.tcl
package require evblite... set evbInstance [evblite::evblite %AUTO% \ -insid 0 -inring rawdata -outring builtdata -dt 1000]
... proc OnStart {} { ... $::evbInstance start
... }
Let's deconstruct this step by step. Note, however, that the example above assumes the script is running in an environment wich includes $DAQROOT/TclLibs in the Tcl package search path. This is the case in ReadoutCallouts.tcl. When using the manager, the container initialization script can source an appropriate daqsetup.tcl and the program definition can define the TCLLIBPATH environment to be $DAQROOT/TclLibs.
- Pulls the evblite package into the script. This package defines a snit type; evblite::evblite to encapsulate each instance od EVBLite. Note that running several EVBLite instances which, in turn, feed a second level event builder is perfectly reasonable.
-
This pair of lines define an event builder instance.
In this case, the event builder is configured as it's instantiated. It is also possibel to use
the objects'
configuresubcommand to configure the event builder after instantiation. Configuration is done using the option database. The full set of options accepted by evblite objects can be found in the refrence pages. We use: - -insid 0
-insidspecifies the input source id. If non physics items are found with no body header, this is the sourcde id that will be put in its fragment header. Note; EVBLite requires that all physics items have body headers.- -inring rawdata
Specifies the ringbuffer (name not URL) that will be the source of data for EVBLite. If a remote ring is desired you can specify the proxy ring for the remote ring in the localhost.
- -outring builtdata
Specifies the name of the ringbuffer into which EVBLite will put built event data. Ringbuffer producers must be local so the ring buffer is specified by name rather than URL.
- -dt 1000
Specifies the event builder coincidence window. Events will all lie in a time interval where their timestamps will be at most 1000ticks larger than the initial fragment.