- Adding first working version of the McStas SICS connection to cvs
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mcstas.tex
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mcstas.tex
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\subsection{McStas Integration}
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It is useful to drive a simulation of an instrument with the same interface as is used at
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the original instruments. One of the better packages for performing simulations of neutron
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scattering instruments, including samples, is McStas. This section describes SICS
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interface to McStas simulations. The interface consists of three parts:
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\begin{itemize}
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\item A McStas controller module which controls the actual simulation.
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\item A McStas reader which is responsible for reading simulated data into
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SICS counters and histogram memories.
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\item Counter and histogram memory drivers which redirect their actions to the
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McStas controller module.
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\end{itemize}
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The general ideas is that all parameters are handled through the normal SICS simulation
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drivers. The counting operations, however, are linked with the McStas simulation.
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\subsubsection{McStas Requirements and SICS Requirements}
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In order for the McStas SICS interface to work the McStas simulation has to be configured
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in a certain way:
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\begin{itemize}
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\item All parameters which have to pass between SICS and McStas have to be declared as
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simulation parameters in the DEFINE INSTRUMENT section of the instrument definition file.
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Alternatively SICS can write the data to be passed to McStas into a file. But then this
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file must be read in the INITIALIZE section of the instrument definition and values must
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be assigned to the appropriate McStas variables.
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\item McStas must dump its data into a single file: use the {\it -f filename} option.
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The format must be {\it --format=\"XML\"}.
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\end{itemize}
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\subsubsection{The McStas Controller}
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The connection to the McStas simulation could have been implemented in the counter,
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HM drivers alone. However, these two implementations would share so much code that it
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deemed advisable to separate this logic into a separate module. The McStas controller is
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basically implementing the Countable SICS interface plus some necessary parameters. In order
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to be as general as possible many operations of the McStas controller are offloaded to
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Tcl scripts in order to achieve support for different types of instruments.
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The following operations will be performed at the various steps:
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\begin{description}
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\item[Start Counting] A script will be called which collects the settings parameters from SICS and
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builds a command line for the McStas simulation. The simulation will then be started. A note
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is made of the PID of the McStas process.
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\item[Status Requests]First thing, status checking maps to running a script which decides
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if the McStas process is still running. Else it is finished. Count control depends
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on the counting mode:
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\begin{description}
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\item[timer mode] Timer mode is handled in SICS internally. The simulation is started with a
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generous number of neutron generations and stopped when the time limit has been reached.
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\item[monitor mode] In monitor mode, the control monitor of McStas is read at regular
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intervalls. Counting is interrupted when the preset monitor has been exceeded.
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\end{description}
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\item[Stopping] Interrupting the simulation is achived by sending the TERM signal to the
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McStas process.
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\item[Data Transfer] Data transfer happens by calling a script which is supposed to use
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the McStas reader for transferring simulation data into SICS counters and histogram
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memories. In order to read data during the runtime of the simulation, the signal USR2
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is sent to the McStas process. This causes McStas to dump a data file. In order for this
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not to happen to frequently, an update intervall is maintained.
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\end{description}
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In order to do its job the McStas controller needs the following data structure:
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\begin{flushleft} \small
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\begin{minipage}{\linewidth} \label{scrap1}
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$\langle$mcconint {\footnotesize ?}$\rangle\equiv$
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\vspace{-1ex}
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\begin{list}{}{} \item
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\mbox{}\verb@@\\
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\mbox{}\verb@ typedef struct{@\\
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\mbox{}\verb@ pObjectDescriptor pDes;@\\
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\mbox{}\verb@ pStringDict scripts;@\\
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\mbox{}\verb@ int updateIntervall;@\\
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\mbox{}\verb@ int pid;@\\
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\mbox{}\verb@ int lastError;@\\
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\mbox{}\verb@ char errorText[256];@\\
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\mbox{}\verb@ CounterMode mode;@\\
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\mbox{}\verb@ float fPreset;@\\
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\mbox{}\verb@ time_t lastUpdate;@\\
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\mbox{}\verb@ time_t startTime;@\\
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\mbox{}\verb@ time_t stopTime;@\\
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\mbox{}\verb@ }McStasController, *pMcStasController;@\\
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\mbox{}\verb@ @$\diamond$
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\end{list}
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\vspace{-1ex}
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\footnotesize\addtolength{\baselineskip}{-1ex}
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\begin{list}{}{\setlength{\itemsep}{-\parsep}\setlength{\itemindent}{-\leftmargin}}
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\item Macro referenced in scrap ?.
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\end{list}
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\end{minipage}\\[4ex]
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\end{flushleft}
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The fields are:
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\begin{description}
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\item[pDes] The usual SICS object descriptor.
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\item[scripts] A dictionary holding the keys and values for all the scripts required.
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\item[updateIntervall] The minimum time to leave between updates.
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\item[pid] The PID of the McStas process. Is negative if the simulation is not running.
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\item[lastError] The last error code.
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\item[mode] The count mode.
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\item[fPreset] The preset value.
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\item[lastUpdate] The time of the last update.
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\item[startTime] The starting time of the counting operation.
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\item[stopTime] The time when counting finished
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\end{description}
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The prototypes for the McStas controller are:
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\begin{flushleft} \small
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\begin{minipage}{\linewidth} \label{scrap2}
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$\langle$mcconproto {\footnotesize ?}$\rangle\equiv$
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\vspace{-1ex}
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\begin{list}{}{} \item
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\mbox{}\verb@@\\
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\mbox{}\verb@ int McStasControllerFactory(SConnection *pCon, SicsInterp *pSics, @\\
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\mbox{}\verb@ void *pData, int argc, char *argv[]);@\\
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\mbox{}\verb@ int McStasControllerWrapper(SConnection *pCon, SicsInterp *pSics, @\\
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\mbox{}\verb@ void *pData, int argc, char *argv[]);@\\
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\mbox{}\verb@@\\
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\mbox{}\verb@ int McStasStart(pMcStasController self, CounterMode mode, float fPreset);@\\
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\mbox{}\verb@ int McStasStatus(pMcStasController self,float *fControl);@\\
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\mbox{}\verb@ int McStasStop(pMcStasController self);@\\
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\mbox{}\verb@ int McStasTransferData(pMcStasController self); @\\
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\mbox{}\verb@ int McStasGetError(pMcStasController self, char *error, int errLen);@\\
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\mbox{}\verb@ int McStasFix(pMcStasController self);@\\
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\mbox{}\verb@ float McStasGetTime(pMcStasController self);@\\
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\mbox{}\verb@ @$\diamond$
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\end{list}
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\vspace{-1ex}
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\footnotesize\addtolength{\baselineskip}{-1ex}
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\begin{list}{}{\setlength{\itemsep}{-\parsep}\setlength{\itemindent}{-\leftmargin}}
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\item Macro referenced in scrap ?.
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\end{list}
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\end{minipage}\\[4ex]
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\end{flushleft}
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The functions implement the interpreter interface to SICS and the required raw functions
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for implementing the countable interface.
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\subsubsection{The McStas Reader}
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A means is needed to map McStas detectors and monitors to SICS monitors and histogram
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memories. This is the purpose of the McStas reader. The McStas reader uses the NeXus-XML
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API in order to traverse the XML hierarchy. Due to problems with the XML format
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written by McStas all data is treated as text. The McStas reader decodes this and assigns the data
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to counter or HM monitors or HM arrays. Most of this modules operation is in the
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interpreter interface. Thus the signature of this module looks like this:
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\begin{flushleft} \small
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\begin{minipage}{\linewidth} \label{scrap3}
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$\langle$mcreadint {\footnotesize ?}$\rangle\equiv$
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\vspace{-1ex}
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\begin{list}{}{} \item
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\mbox{}\verb@@\\
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\mbox{}\verb@typedef struct {@\\
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\mbox{}\verb@ pObjectDescriptor pDes;@\\
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\mbox{}\verb@ NXhandle handle;@\\
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\mbox{}\verb@ char nexusError[1024];@\\
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\mbox{}\verb@ }McStasReader, *pMcStasReader;@\\
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\mbox{}\verb@/*-----------------------------------------------------------------------------*/@\\
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\mbox{}\verb@ int McStasReaderFactory(SConnection *pCon, SicsInterp *pSics, @\\
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\mbox{}\verb@ void *pData, int argc, char *argv[]);@\\
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\mbox{}\verb@ int McStasReaderWrapper(SConnection *pCon, SicsInterp *pSics, @\\
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\mbox{}\verb@ void *pData, int argc, char *argv[]); @\\
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\mbox{}\verb@ @$\diamond$
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\end{list}
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\vspace{-1ex}
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\footnotesize\addtolength{\baselineskip}{-1ex}
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\begin{list}{}{\setlength{\itemsep}{-\parsep}\setlength{\itemindent}{-\leftmargin}}
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\item Macro referenced in scrap ?.
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\end{list}
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\end{minipage}\\[4ex]
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\end{flushleft}
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\begin{flushleft} \small
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\begin{minipage}{\linewidth} \label{scrap4}
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\verb@"mccontrol.h"@ {\footnotesize ? }$\equiv$
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\vspace{-1ex}
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\begin{list}{}{} \item
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\mbox{}\verb@@\\
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\mbox{}\verb@ /*--------------------------------------------------------------------------------------@\\
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\mbox{}\verb@ McSas simulation to SICS controller module header file. For more details see @\\
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\mbox{}\verb@ mcstas.tex. @\\
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\mbox{}\verb@@\\
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\mbox{}\verb@ copyright: see file COPYRIGHT@\\
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\mbox{}\verb@ @\\
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\mbox{}\verb@ Mark Koennecke, June 2005@\\
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\mbox{}\verb@----------------------------------------------------------------------------------------*/@\\
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\mbox{}\verb@#ifndef MCSTASCONTROL@\\
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\mbox{}\verb@#define MCSTASCONTROL@\\
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\mbox{}\verb@#include "sics.h"@\\
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\mbox{}\verb@#include "countdriv.h"@\\
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\mbox{}\verb@#include "stringdict.h"@\\
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\mbox{}\verb@/*--------------------- data structure -------------------------------------------------*/@\\
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\mbox{}\verb@@$\langle$mcconint {\footnotesize ?}$\rangle$\verb@@\\
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\mbox{}\verb@/*---------------------- function prototypes -------------------------------------------*/@\\
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\mbox{}\verb@@$\langle$mcconproto {\footnotesize ?}$\rangle$\verb@@\\
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\mbox{}\verb@#endif@\\
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\mbox{}\verb@@\\
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\mbox{}\verb@@$\diamond$
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\end{list}
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\vspace{-2ex}
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\end{minipage}\\[4ex]
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\end{flushleft}
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\begin{flushleft} \small
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\begin{minipage}{\linewidth} \label{scrap5}
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\verb@"mcreader.h"@ {\footnotesize ? }$\equiv$
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\vspace{-1ex}
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\begin{list}{}{} \item
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\mbox{}\verb@@\\
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\mbox{}\verb@ /*---------------------------------------------------------------------------------@\\
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\mbox{}\verb@ Header file for the McStas reader module. This module helps transferring McStas@\\
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\mbox{}\verb@ result data into SICS counters and histogram memories.@\\
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\mbox{}\verb@@\\
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\mbox{}\verb@ copyright: see file COPYRIGHT@\\
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\mbox{}\verb@@\\
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\mbox{}\verb@ Mark Koennecke, June 2005@\\
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\mbox{}\verb@-------------------------------------------------------------------------------------*/@\\
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\mbox{}\verb@#ifndef MCSTASREADER @\\
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\mbox{}\verb@#define MCSTASREADER@\\
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\mbox{}\verb@#include "sics.h"@\\
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\mbox{}\verb@#include "napi.h"@\\
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\mbox{}\verb@@$\langle$mcreadint {\footnotesize ?}$\rangle$\verb@@\\
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\mbox{}\verb@#endif@\\
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\mbox{}\verb@@\\
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\mbox{}\verb@ @$\diamond$
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\end{list}
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\vspace{-2ex}
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\end{minipage}\\[4ex]
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\end{flushleft}
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