- Adding first working version of the McStas SICS connection to cvs
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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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\item In order to count on monitor, a modified PSD_monitor component MUST be used in the
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simulation. This component writes the collected total counts into a file. This file is
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the read by SICS in order to determine the control monitor. Evaluating the McStas XML dump \
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file each time proved to be to inaccurate.
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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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@d mcconint @{
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typedef struct{
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pObjectDescriptor pDes;
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pStringDict scripts;
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int updateIntervall;
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int pid;
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int lastError;
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char errorText[256];
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CounterMode mode;
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float fPreset;
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time_t lastUpdate;
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time_t startTime;
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time_t stopTime;
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}McStasController, *pMcStasController;
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@}
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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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@d mcconproto @{
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int McStasControllerFactory(SConnection *pCon, SicsInterp *pSics,
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void *pData, int argc, char *argv[]);
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int McStasControllerWrapper(SConnection *pCon, SicsInterp *pSics,
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void *pData, int argc, char *argv[]);
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int McStasStart(pMcStasController self, CounterMode mode, float fPreset);
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int McStasStatus(pMcStasController self,float *fControl);
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int McStasStop(pMcStasController self);
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int McStasTransferData(pMcStasController self);
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int McStasGetError(pMcStasController self, char *error, int errLen);
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int McStasFix(pMcStasController self);
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float McStasGetTime(pMcStasController self);
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@}
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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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@d mcreadint @{
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typedef struct {
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pObjectDescriptor pDes;
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NXhandle handle;
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char nexusError[1024];
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}McStasReader, *pMcStasReader;
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/*-----------------------------------------------------------------------------*/
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int McStasReaderFactory(SConnection *pCon, SicsInterp *pSics,
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void *pData, int argc, char *argv[]);
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int McStasReaderWrapper(SConnection *pCon, SicsInterp *pSics,
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void *pData, int argc, char *argv[]);
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@}
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@o mccontrol.h @{
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/*--------------------------------------------------------------------------------------
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McSas simulation to SICS controller module header file. For more details see
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mcstas.tex.
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copyright: see file COPYRIGHT
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Mark Koennecke, June 2005
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----------------------------------------------------------------------------------------*/
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#ifndef MCSTASCONTROL
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#define MCSTASCONTROL
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#include "sics.h"
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#include "countdriv.h"
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#include "stringdict.h"
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/*--------------------- data structure -------------------------------------------------*/
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@<mcconint@>
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/*---------------------- function prototypes -------------------------------------------*/
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@<mcconproto@>
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#endif
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@}
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@o mcreader.h @{
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/*---------------------------------------------------------------------------------
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Header file for the McStas reader module. This module helps transferring McStas
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result data into SICS counters and histogram memories.
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copyright: see file COPYRIGHT
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Mark Koennecke, June 2005
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-------------------------------------------------------------------------------------*/
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#ifndef MCSTASREADER
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#define MCSTASREADER
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#include "sics.h"
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#include "napi.h"
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@<mcreadint@>
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#endif
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@}
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