areaDetector Plugin NDPluginFile

Contents

• Overview
• Configuration
• Screen shots

Overview

NDPluginFile saves the NDArray data from a callback to a disk file.

NDPluginFile inherits from NDPluginDriver. This plugin currently saves data in the netCDF file format, which is a portable self-describing binary file format supported by UniData at UCAR (University Corporation for Atmospheric Research). Additional file formats, such as TIFF and HDF may be supported in the future.

The NDArray callback data can be written to disk in 1 of 3 modes:

1. Single mode. In this mode each NDArray callback results in a separate disk file.
2. Capture mode. In this mode a memory buffer is allocated before saving begins. Callback arrays are placed into this buffer, and when capture stops the file is written to disk. This mode limits the number of frames that can be saved, because they all must fit in a memory buffer. It is the fastest mode, with the least probability of dropping arrays, because no disk I/O is required while capture is in progress.
3. Stream mode. In this mode the data are written to a single disk file, with each frame being appended to the file without closing it. It is intermediate in speed between single mode and capture mode, but unlike capture mode it is not limited by available memory in the number of arrays that can be saved.

The NDPluginFile public interface is defined in NDPluginFile.h as follows:

/* Note that the file format enum must agree with the mbbo/mbbi records in the NDFile.template file */
typedef enum {
    NDFileFormatNetCDF,
} NDPluginFileFormat_t;

typedef enum {
    NDPluginFileModeSingle,
    NDPluginFileModeCapture,
    NDPluginFileModeStream
} NDPluginFileMode_t;

...
class NDPluginFile : public NDPluginDriver {
public:
    NDPluginFile(const char *portName, int queueSize, int blockingCallbacks, 
                 const char *NDArrayPort, int NDArrayAddr);
                 
    /* These methods override those in the base class */
    void processCallbacks(NDArray *pArray);
    asynStatus writeInt32(asynUser *pasynUser, epicsInt32 value);
    asynStatus writeNDArray(asynUser *pasynUser, void *genericPointer);
    asynStatus drvUserCreate(asynUser *pasynUser, const char *drvInfo, 
                             const char **pptypeName, size_t *psize);

...
}

NDPluginFile also supports all of the file saving parameters defined in ADStdDriverParams.h described above, e.g.ADFilePath, ADFileName, etc. Thus, the same interface that is used for saving files directly in a driver are used for this plugin.

Configuration

The NDPluginFile plugin is created with the following command, either from C/C++ or from the EPICS IOC shell.

drvNDFileConfigure(const char *portName, int queueSize, int blockingCallbacks, 
                   const char *NDArrayPort, int NDArrayAddr)
  

Screen shots

The following is the MEDM screen that provides access to the parameters in NDPluginDriver.h and NDPluginFile.h through records in NDPluginBase.template and NDFile.template. This is the MEDM screen that is used to control the saving of images to disk for drivers that do not support saving files to disk themselves.