Fast Control System Simulation Data for Reco (April 1997)
Overview
The Fast Control System simulation consists of two parts: the simulation of the clocks and the simulation of a trigger result, which can be used together to determine what data will actually be read by DAQ from each subsystem. These parts are contained
within the FcsSim and FcsData packages, and use the BaBar/BbrTime and TrgData/TrgWord classes.
The FCclock simulation is a package which allows conversion between beam crossings, nanoseconds, and clock ticks, while taking into account the random offsets between the beam crossing which causes an event and the rising edge of the first clock.
Examples of how it can be used can be found in SvtSim, trgEM, trgDC, TrgSim, and in FcsSim itself.
The trigger result consists of the trigger word (i.e. the lines after prescaling), along with the absolute time of the Level 1 Accept. These quantities are recorded in the AbsEvtObj FcsDigi. At the present, the time quantity is filled with the current
time of day, as no standard for the time of a GEANT event has been agreed upon, and thus no absolute time for the Level 1 Accept can be calculated.
FcsSim also creates the AbsEvtObj FcsSimOut, which contains the calculated time of the Level 1 Accept relative to GEANT physics time; this is a simulation-only quantity. By default, this is a random number in a flat distribution between 0 ns and -1000
ns (approximately the jitter requirement); this can be changed to use the full trigger simulation to determine the event time, to use a Gaussian distribution, or to shrink the range of random numbers.
See FcsSim/README file for more details.
Users
Currently, the clocks and trigger simulation objects are used by the Svt simulation and by the Trg simulation to determine which data will be seen in the DAQ stream. The Trg simulation uses the time calculated by the global trigger simulation, while the
Svt simulation uses the random distribution, although it can easily be switched to use the full simulation ; the FcsDigi is currently unused. |
