Added a description of parameters affecting M0 operation (comments only)

RecoLocalCalo/HcalRecProducers/python/HBHEMethod0Parameters_cfi.py

@@ -1,6 +1,52 @@
 import FWCore.ParameterSet.Config as cms
 
-# Configuration parameters for Method 0
+# Behavior of "Method 0" depends on the following top-level
+# HBHEPhase1Reconstructor parameters:
+#
+# (bool) tsFromDB
+# (bool) recoParamsFromDB
+#
+# and on the following parameters inside the "algorithm" parameter set,
+# defined as m0Parameters below:
+#
+# (int) firstSampleShift
+# (int) samplesToAdd
+# (bool) correctForPhaseContainment
+# (double) correctionPhaseNS
+#
+# The role of "tsFromDB" parameter is to specify whether the
+# "sample of interest" (SOI) should be taken from the data frame
+# (in case tsFromDB is False) or from the database (tsFromDB is True).
+# Once SOI is determined in this manner, the time slice for starting
+# the ADC charge summation (TSS) is determined by adding SOI and
+# "firstSampleShift". "firstSampleShift" can be negative, and if
+# TSS = SOI + firstSampleShift ends up negative, TSS is reset to 0.
+# If you want to start summation from time slice 0, just set
+# "firstSampleShift" to some negative number with large magnitude.
+#
+# In the old reco code, it used to be possible to configure the TSS
+# using a parameter value. This is no longer the case for Phase 1
+# reconstructor.
+#
+# The values of the remaining M0 parameters, "samplesToAdd",
+# "correctForPhaseContainment", and "correctionPhaseNS", will be
+# taken from the configuration file only if "recoParamsFromDB"
+# is set to False. If "recoParamsFromDB" is True, the config
+# file values of these parameters are ignored, and these values
+# are instead taken from the database. The "samplesToAdd" parameter
+# defines how many contiguous time slices will be used to calculate
+# the charge. TSS + samplesToAdd should not exceed the number of
+# time slices in the data frame, otherwise M0 will still work but
+# the results will be unreliable.
+#
+# Parameter "correctForPhaseContainment" specifies whether
+# a correction should be made for incomplete HPD signal collection
+# inside the summed time slices, and "correctionPhaseNS" specifies
+# the delay (in ns) of the HPD signal w.r.t. the ADC digitization
+# clock edge. That is, in the reco code, increasing correctionPhaseNS
+# moves reco window to the left w.r.t. the signal (AFAIK, the behavior
+# of PhaseDelay QIE11 configuration register is the opposite).
+#
 m0Parameters = cms.PSet(
     firstSampleShift = cms.int32(0),
     samplesToAdd = cms.int32(2),