areaDetector Plugin NDPluginAttribute

March 8, 2014

Matt Pearson, Oak Ridge National Lab

Mark Rivers, University of Chicago



This plugin provides the ability to extract an NDArray attributes and publish their values over channel access. It also publishes arrays of the attribute values, and the integrated values.

Each NDPluginAttribute plugin supports any number of attributes, each publishing the last attribute value, the sum of that attribute value since the last reset, and a time-series array of the attribute value. The number of attributes is defined when the NDPluginAttribute is created in the startup script. Each attribute is referenced by its asyn "addr" address field.

In addition to the actual NDAttributes attached to the NDArray this plugin supports 4 virtual attributes. These correspond to properties of all NDArray objects. These virtual attribute names can use used in the $(P)$(R)AttrName record to select that NDArray property.

Virtual attribute name NDArray property
NDArrayUniqueId NDArray.uniqueId
NDArrayTimeStamp NDArray.timeStamp
NDArrayEpicsTSSec NDArray.epicsTS.secPastEpoch
NDArrayEpicsTSnSec NDArray.epicsTS.nsec

The time-series arrays use the same PVs to control acquisition as the NDPluginStats plugin. Acquisition of arrays for all attributes are started an stopped at the same time.

NDPluginAttribute inherits from NDPluginDriver. The NDPluginAttribute class documentation describes this class in detail.

NDPluginAttribute defines the following parameters. It also implements all of the standard plugin parameters from NDPluginDriver.

Parameter Definitions in NDPluginAttribute.h and EPICS Record Definitions in NDAttribute.template
Parameter index variable asyn interface Access Description drvInfo string EPICS record name EPICS record type
asynInt32 r/w Reset the plugin data. This zeros the array, and resets the value sum and value to zero. ATTR_RESET $(P)$(R)Reset bo
Time-Series data
The time series is implemented by loading an instance of the NDPluginTimeSeries for each NDPluginStats plugin, and the time series control uses records in NDTimeSeries.template. That documentation should be consulted for an explanation of these records. The prefix and record name macro for the time-series plugin records from NDTimeSeries.template is $(P)$(R)TS:.
NOTE: The time-series plugin is often used with drivers which sample at a fixed well-defined time interval. This cannot be guaranteed with the statistics plugin, so the averaging time records and time axis waveform record from NDPluginTimeSeries are typically not used, and the statistics data are plotted against time point #, rather than actual time.
The time-series waveform records for each statistic are defined in NDAttributeN.template.
asynFloat64Array r/o The time series data arrays of the basic statistics and centroid and sigma statistics described above. TS_TIME_SERIES $(P)$(R)TSArrayValue waveform
Parameter Definitions in NDPluginAttribute.h and EPICS Record Definitions in NDAttributeN.template. There is one of these records for each attribute in the plugin.
Parameter index variable asyn interface Access Description drvInfo string EPICS record name EPICS record type
NDPluginAttributeAttrName asynOctet r/w The name of the NDAttribute parameter that we want to publish. This can be modified at runtime. ATTR_ATTRNAME $(P)$(R)AttrName
NDPluginAttributeVal asynFloat64 r/o Attribute value ATTR_VAL $(P)$(R)Value_RBV ai
NDPluginAttributeValSum asynFloat64 r/o Sum of the attribute value, since the last reset. ATTR_VAL_SUM $(P)$(R)ValueSum_RBV ai

If the array data contains more than 16K bytes then in order for EPICS clients to receive this data they must be built with EPICS R3.14 (not R3.13), and the environment variable EPICS_CA_MAX_ARRAY_BYTES on both the EPICS IOC computer and EPICS client computer must be set to a value at least as large as the array size in bytes.


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

NDAttrConfigure(const char *portName, int queueSize, int blockingCallbacks, 
                      const char *NDArrayPort, int NDArrayAddr, int maxAttributes, 
                      int maxBuffers, size_t maxMemory, int priority, int stackSize)

All arguments except maxAttributes are common to all plugins. maxAttributes defines the maximum number of attributes that this plugin will support.

For details on the meaning of the parameters to this function refer to the detailed documentation on the NDAttrConfigure function in the NDPluginAttribute.cpp documentation and in the documentation for the constructor for the NDPluginAttribute class.

Screen shots

The following is the MEDM screen that provides access to the parameters in NDPluginDriver.h and NDPluginAttribute.h through records in NDPluginBase.template and NDAttribute.template.



The following is the MEDM screen that provides control and display of the parameters for 8 attributes.



The following is the MEDM screen that displays the time-series data for each attribute. The first screen shows a plot of NDArrayUniqueID and the second shows NDArrayEpicsTSnSec.


NDPluginAttributeTSUniqueID.png NDPluginAttributeTSEpicsTSnSec.png