Draft, in work.
Generating Xtc
For tutorial purposes, the following streamlined example shows XXX. For an example involving more detectors, formats and algorithms, see xtcdata/xtcdata/app/xtcwriter.cc.
A Notional DAQ Harness
Let's motivate the example. Assume we're developing a an Xtc writer class to output CSPAD data. This class will get plugged in to a (notional) DAQ framework.
# Assume some totally made-up data acquisition callback framework named DAQFramework # Developers of the psdaq package are welcome to come in and change this toy example # to match the real DAQ API. CSPADXtcWriter padwriter() DAQFramework.registerHandler("configure", padwriter.setup) DAQFramework.registerHandler("runstart", std::bind(padwriter.openXtcFile, filename)) DAQFramework.registerHandler("readout", padwriter.writeImage) DAQFramework.registerHandler("runend", padwriter.closeXtcFile)
"setup" Method: Set Up The Names Structure
Register the algorithms and "shape" of the data associated with detector elements to tell the processing pipeline how to process.
- First some plumbing...
- Create an XtcData:Dgram as the root container.
- Next code sample description.
At some initialization step, for example in response to a DAQ configure signal:
- Subclass XtcData::VarDef to build a data structure specific to the detector in question.
"writeImage" Method: Add Readout Data
Parsing Whole Xtc Files
xtcreader.cc and XtcIterator.hh
Use of Xtc Small Data Files
this might be duplicate of what's on top page
Notes for Real-World Code
Realistic Xtc Writers
- Thread safety issue #1
- Thread safety issue #2
- (You'll likely need to sub-class from XYZ in order to ABC)
Realistic Xtc Readers
- Thread safety issue #1
- Thread safety issue #2
- (You'll likely need to sub-class from XYZ in order to ABC)
Full "Hello Xtc" Code Listings
CSPADXtcWriter Example
#include "xtcdata/xtc/ShapesData.hh" #include "xtcdata/xtc/DescData.hh" #include "xtcdata/xtc/Dgram.hh" #include "xtcdata/xtc/TypeId.hh" #include "xtcdata/xtc/XtcIterator.hh" #include "xtcdata/xtc/VarDef.hh" using namespace XtcData; #define BUFSIZE 0x4000000 CSPADXtcWriter::CSPADXtcWriter() { // Squirrel away algorithm definitions in a VarDef class PadDef:public VarDef { enum index { arrayRaw }; PadDef() { Alg segmentAlg("caspadseg",2,3,42); // alg name, major, minor, patch) // We get a NameVec by subclassing from VarDef NameVec.push_back({"arrayRaw", segmentAlg}); } }; // Define some instance variables. FILE *this->xtcoutfile; Dgram& this->configDgram; std::vector<NameIndex>& this->namesVec; this->PadDef = new PadDef(); // Now initialize various things _initializeConfigDgram(); } void CSPADXtcWriter::_initializeConfigDgram() { void* configbuf = malloc(BUFSIZE); this->configDgram = *(Dgram*)configbuf; this->configDgram.xtc.contains = tid; this->configDgram.xtc.damage = 0; this->configDgram.xtc.extent = sizeof(Xtc); } void CSPADWriter::_addNames(Xtc& parent, std::vector<NameIndex>& namesVec) { } void CSPADXtcWriter::setup() { _addNames(this->configDgram.xtc, this->namesVec); } void CSPADXtcWriter::openXtcFile(xtcoutfilename) { this->xtcoutfile = fopen(xtcoutfilename, "w"); } void CSPADXtcWriter::writeImage() { } void CSPADXtcWriter::closeXtcFile() { fclose(this->xtcoutfile); }
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