L1Calo Bytestream Decoding in ATHENA

This is a quick summary of the key features of the present bytestream decoding in ATHENA.

ATHENA Packages

Trigger/TrigT1/TrigT1Result

This contains the L1Calo "Raw Data Objects" (RDOs) which are implemented as various subclasses of a base class L1CaloRdo. All objects are contained in a store of type L1CaloRdoStore. The decoding from ROD fragments to create the RDOs is done by the (templated) L1CaloBsDecoder class.

These classes are directly copied from the online bytestreamDecoder package with only two changes:

• five trivial subclasses of L1CaloRdoStore were created so that five different ROD fragments could be converted using the simple conversion mechanism
• Gaudi CLASSDEF infrastructure was added to the L1CaloRdoStore class and the new subclasses so they could be stored in StoreGate

Trigger/TrigT1/TrigT1CaloTestBeam

This package contains two different things (which should probably be separated).

• ATHENA bytestream decoder infrastructure (more details below)
• algorithm(s) for analysing the data: this is where most people will add their own code

Bytestream Decoder Infrastructure

We use the simplest bytestream decoding infrastructure. This allows one ROD fragment to be converted to one object of one class and stored in StoreGate. Since we have four (might have been five) different types of ROD fragment, we needed to replicate the infrastructure five times.

For each fragment we have the following:

• L1CaloSrcIdMap:
  single class for all five fragments contains the mapping between ROD source IDs and ROB source IDs. It also has some enums defined the ROD sources IDs which are used in the conversion service and tool classes.
• RecL1CaloXXXXXXByteStreamCnv:
  conversion service for fragment of type XXXXXX, where XXXXXX is one of CmmDaq, CpmDaq, CpmRoi, JemDaq, PpmDaq. This class handles the mapping between ROB and ROD fragments and then uses the associated tool class to perform the conversion.
• RecL1CaloXXXXXXByteStreamTool:
  conversion tool for fragment of type XXXXXX (as above). This invokes the L1CaloBsDecoder to perform the conversion and stores the appropriate L1CaloRdoStoreXXXXXX subclass in StoreGate.
• src/components/TrigT1CaloTestBeam_entries:
  This file sets up the Gaudi dynamic library and class registration. Each of the five conversion services needs entries as follows:
    #include "RecL1CaloXXXXXXByteStreamCnv.h"
  DECLARE_CONVERTER_FACTORY(RecL1CaloXXXXXXByteStreamCnv);
  DECLARE_FACTORY_ENTRIES(TrigT1CaloTestBeam) {
    DECLARE_CONVERTER(RecL1CaloXXXXXXByteStreamCnv);
  }

• jobOptions:
  Each of the five decoders needs to be declared in the jobOptions file so that StoreGate knows about the class and its associated key. This allows it to create a proxy for the object which is returned when a request is made for an object with that key. The bytestream conversion is only done when a method of the object is called, ie the object is really needed. The jobOptions entry is:
    ByteStreamAddressProviderSvc = Service( "ByteStreamAddressProviderSvc" )
  ByteStreamAddressProviderSvc.TypeNames += ["L1CaloRdoStoreXXXXXX/L1CaloRawDataXXXXXX"]
  ByteStreamCnvSvc = Service( "ByteStreamCnvSvc" )
  ByteStreamCnvSvc.InitCnvs += [ "L1CaloRdoStoreXXXXXX" ]
NB in the TypeNames entries the first element in the classname (eg L1CaloRdoStoreXXXXXX for a particular L1CaloRdoStore subclass) and the second (eg L1CaloRawDataXXXXXX) is the key to be used when requesting the object from StoreGate.
  The TrigT1CaloTestBeam/share directory contains a suitable jobOptions fragment declaring all five converters.

Using the Decoders

With all the above infrastructure in place, using the decoders is fairly simple. Just ask StoreGate for the key associated with the data you want. This returns a (smart) pointer to the corresponding L1CaloRdoStore subclass containing the L1CaloRdo objects decoded from the relevant ROD fragment.

  // Store Gate active store: in algorithm initialise() method.
  sc = serviceLocator()->service("ActiveStoreSvc", m_activeStore);
  if (sc.isFailure()) { // handle error }
  
  // Get store of CPM DAQ data from StoreGate
  const DataHandle myL1CaloRdoStoreCpmDaq;
  sc = (*m_activeStore)->retrieve(myL1CaloRdoStoreCpmDaq, "L1CaloRawDataCpmDaq");
  if (sc.isFailure()) { // handle error }
  
  // Use L1CaloRdoStore API to iterate over CPM DAQ data
  CpmTowerIter beginCT, endCT;
  myL1CaloRdoStoreCpmDaq->getCpmTowerIterators( beginCT, endCT );
  while ( beginCT != endCT ) { // analyse data }