Midas Event Builder

The Midas event builder is responsible for assembling the event fragments (obtained from the shared memory segments BUF1-BUF7) into complete events (deposited in the shared memory segment SYSTEM).

Since different configurations of running frontend processes are possible a flexible scheme for fragment assembly is required. In Midas a mask is used to inform the event builder which fragments to assemble. The mask is located in the "EBuilder/Settings" sub-directory of the event builder ODB entry. In µLan a mask of 0x7F says assemble all seven fragments while a mask of 0x41 says assemble WFD01 and CAEN fragments only. In µlan the appropriate mask is automatically determined via the "common/enabled" ODB entries for every frontend process. This bit is set to one if the corresponding frontend process is running and set to zero if the corresponding frontend process is stopped.

The event builder is started either from the programs page of the Midas web interface or by typing "./mevb -e mulan" in the sub-directory /home/mulan/muLan/EventBuilder on the backend machine. The Midas status page displays if the Midas event builder is active (green background) or inactive (red background). It also has statistics on the numbers and rates for event building.