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MUON Raw data

How to read & decode raw data

The macros MUONRawStreamTracker.C and MUONRawStreamTrigger.C can be used to read & decode DDL files and root files. DATE files are no more supported.

For tracker raw data, full output

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTracker.C+
MUONRawStreamTrackerExpert(rawFileName, maxEvent, firstDDL, lastDDL)

For tracker raw data, just digit output

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTracker.C+
MUONRawStreamTrackerSimple(rawFileName, maxEvent, firstDDL, lastDDL)

There is also a high performance decoder available, which can be run as follows for full output:

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTracker.C+
MUONRawStreamTrackerHPExpert(rawFileName, maxEvent, firstDDL, lastDDL)

And just for digit output like so:

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTracker.C+
MUONRawStreamTrackerHPSimple(rawFileName, maxEvent, firstDDL, lastDDL)

The MUONRawStreamTracker.C macro also provides other alternative implementations for fetching the decoded data from the high performance decoder's interface. These generate the same output, but show how to write code to fetch the data in various ways from the interface. Developers should consult the macro as an example of how to use the interface. The alternate methods are called:

MUONRawStreamTrackerHPExpert2()
MUONRawStreamTrackerHPExpert3()
MUONRawStreamTrackerHPSimple2()

For trigger raw data, full output

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTrigger.C+ 
MUONRawStreamTrigger(maxEvent, firstDDL, lastDDL, rawFileName)

For trigger raw data, local response output

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTrigger.C+ 
MUONRawStreamTriggerSimple(maxEvent, rawFileName)

Similarly there is a high performance decoder available for the trigger DDLs, which can be run as follows for full output:

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTrigger.C+
MUONRawStreamTriggerHPExpert(maxEvent, firstDDL, lastDDL, rawFileName)

And just for local response output like so:

.includepath $ALICE_ROOT/STEER
.includepath $ALICE_ROOT/MUON
.includepath $ALICE_ROOT/RAW
.L $ALICE_ROOT/MUON/MUONRawStreamTrigger.C+
MUONRawStreamTriggerHPSimple(maxEvent, rawFileName)

The MUONRawStreamTrigger.C macro also provides other alternative implementations for fetching the decoded data from the trigger high performance decoder's interface. These generate the same output, but show how to write code to fetch the data in various ways from the interface. Developers should consult the macro as an example of how to use the interface. The alternate methods are called:

MUONRawStreamTriggerHPExpert2()
MUONRawStreamTriggerHPExpert3()
MUONRawStreamTriggerHPSimple2()

Default wise the macros read all DDL files from the current directory for 1000 events. For root file rawFileName must end with .root. For DDL files you have to specified the directory where the raw0...n subdirectories are located:

MUONRawStreamTracker(..)(maxEvent, firstDDL, lastDDL, "$YOUR_WORKING_DIRECTORY/"); //Do not forget the slash at the end!

Timing of the raw data decoders

The macro MUONTimeRawStreamTracker.C and MUONTimeRawStreamTrigger.C can used to check the timing (speed) performance of the existing offline decoders compared to the new high performance decoders. For the tracker DDLs the MUONTimeRawStreamTracker.C macro compares the timing of AliMUONRawStreamTracker against the high performance AliMUONRawStreamTrackerHP decoder. Similarly the MUONTimeRawStreamTrigger.C macro compares the timing of the existing AliMUONRawStreamTrigger decoder against the high performance AliMUONRawStreamTrackerHP decoder. The macros can be invoked as follows:

 $ aliroot
.L $ALICE_ROOT/MUON/MUONTimeRawStreamTracker.C+
 MUONTimeRawStreamTracker(filename, maxEvent);
.L $ALICE_ROOT/MUON/MUONTimeRawStreamTrigger.C+
 MUONTimeRawStreamTrigger(filename, maxEvent);

where filename is the name of a file containing the raw data, or alternatively the directory containing rawX (X being an integer) paths with the raw DDL data. The maxEvent value is the maximum event to process (default set to 1000). Thus the macro will time the algorithm for all events in the range [0 .. maxEvent-1].

Special flags for high performance tracker and trigger DDL decoders.

There are three flags that are available through the AliMUONRawStreamTrackerHP interface, which effect the decoding of raw data in special ways.

  • TryRecover (default = false)
  • AutoDetectTrailer (default = true)
  • CheckForTrailer (default = true)

The TryRecover flag is used to enable special logic in the decoder that tries to recover from a partially corrupt raw data structure header, or a corrupt/missing end of DDL trailer. Normally if the header is found to be corrupt (by seeing that the block lengths do not correspond), then the whole corresponding structure is skipped and we move on to the next structure that we are sure of, or skip the rest of the DDL. With the option to recover turned on, we attempt to figure out what the correct values for the structure length should have been. This is possible because there is redundant information in the headers giving the structure size. This recovery procedure will work for single bit flips found inside the headers, but obviously with more severe corruption, the header will not be recoverable. The TryRecover flag is set to kFALSE by default to disable this feature, meaning any structures in the raw data that cause problems in any way are skipped by default. More details about the corrupt header recovery procedure can be found in the method documentation AliMUONTrackerDDLDecoder::TryRecoverStruct().

The AutoDetectTrailer and CheckForTrailer flags are used to deal with the difference in raw data format from the real tracker chambers and the simulated data generated with AliRoot up to March 2008. The end of DDL trailer words are missing in the simulated raw data in the older versions of AliRoot. To tell the decoder that it should expect the trailer words as generated by the real readout electronics then the CheckForTrailer flag should be set to kTRUE (this is the default). If the trailer words are missing in the raw data then CheckForTrailer should be kFALSE. Alternatively one can set the flag AutoDetectTrailer to kTRUE (which is the default) so that the decoder will try to autodetect if the trailer words are there or not. When AutoDetectTrailer is set to kTRUE then the CheckForTrailer flag is ignored. Only when AutoDetectTrailer is set to kFALSE will the CheckForTrailer flag have an effect.

Each of these decoder flags can be set to kTRUE or kFALSE, or tested by the corresponding setter and getter methods respectively. For example, to set the TryRecover flag to kTRUE and fetch its value afterwards, use the following code:

// to set the flag:
decoder.TryRecover(kTRUE);
// or to get the value of the flag:
Bool_t value = decoder.TryRecover();

Similarly, the other flags are manipulated with corresponding methods having the same name as the flag.

The trigger DDL decoder AliMUONRawStreamTriggerHP has the following flag available:

  • TryRecover (default = false)

For the AliMUONRawStreamTriggerHP decoder the TryRecover flag can be set in the same way as for AliMUONRawStreamTrackerHP, with a call to the TryRecover() method. For trigger DDLs this option will enable logic, which attempts to find the next correct header / structure marker key in the DDL stream, whenever such a marker has been found corrupt or missing. Decoding then continues from the new location found or stops if no good key was found. The default setting is to disable this logic, since it is only useful to try recover corrupted data.

Note
Raw data containing software scalars (Start-of-Data events for example) from the trigger detector taken during the Feb-March 2008 cosmics run is corrupt, but can be successfully decoded by enabling this TryRecover flag for the trigger DDL decoder.

This chapter is defined in the READMEraw.txt file.