NDPluginCircularBuff
====================
:author: Edmund Warrick, Diamond Light Source and Mark Rivers, University of Chicago
.. contents:: Contents
Overview
--------
NDPluginCircularBuff is a triggering plugin. It receives NDArrays from a
plugin or driver and checks whether a user-defined trigger condition has
been met. The trigger condition is based on the values of up to two
NDAttributes attached to the NDArray. The attribute values are used in a
general calculation expression that defines the trigger condition. Once
the trigger condition is detected the plugin outputs the triggering
NDArray, along with a configurable number of pre- and post-trigger
NDArrays. Triggering can also be performed using a soft trigger,
controlled from the "Trigger" database record.
Acquisition is started by setting the "NDCircBuffControl" parameter to
non-zero (via the "Capture" record in the associated database). The
plugin then copies all received NDArrays to its ring buffer, wrapping
once the specified pre-count is reached.
Once the trigger is detected, the plugin will immediately output all the
NDArrays stored in the ring buffer in order from oldest to newest (by
calling doCallbacksGenericPointer). After the trigger is set, new
NDArrays will then be output as soon as they arrive, until the
post-count is reached. The plugin will then stop buffering or outputting
NDArrays until it is restarted via NDCircBuffControl. The plugin will
also automatically restart if the following condition is true:
::
(PresetTriggerCount == 0) || ((PresetTriggerCount > 0) && (ActualTriggerCount < PresetTriggerCount)))
NDPluginCircularBuff inherits from NDPluginDriver. The
`NDPluginCircularBuff class
documentation <../areaDetectorDoxygenHTML/class_n_d_plugin_circular_buff.html>`__
describes this class in detail.
NDPluginCircularBuff defines the following parameters. It also
implements all of the standard plugin parameters from
:doc:`NDPluginDriver`. The EPICS database
NDCircularBuff.template provides access to these parameters, listed in
the following table.
.. |br| raw:: html
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.. flat-table::
:header-rows: 2
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* -
- Parameter Definitions in NDPluginCircularBuff.h and EPICS Record Definitions in
NDCircularBuff.template
* - Parameter index variable
- asyn interface
- Access
- Description
- drvInfo string
- EPICS record name
- EPICS record type
* - NDCircBuffControl
- asynInt32
- r/w
- Toggle triggering & buffering on/off
- CIRC_BUFF_CONTROL
- $(P)$(R)Capture, $(P)$(R)Capture_RBV
- busy, bi
* - NDCircBuffStatus
- asynOctet
- r/o
- Plugin status feedback string
- CIRC_BUFF_STATUS
- $(P)$(R)StatusMessage
- stringin
* - NDCircBuffPreTrigger
- asynInt32
- r/w
- Number of pre-trigger NDArrays to store
- CIRC_BUFF_PRE_TRIGGER
- $(P)$(R)PreCount, $(P)$(R)PreCount_RBV
- longout, longin
* - NDCircBuffPostTrigger
- asynInt32
- r/w
- Number of post-trigger NDArrays to output
- CIRC_BUFF_POST_TRIGGER
- $(P)$(R)PostCount, $(P)$(R)PostCount_RBV
- longout, longin
* - NDCircBuffTriggerA
- asynOctet
- r/w
- Name of the NDAttribute for trigger A.
- CIRC_BUFF_TRIGGER_A
- $(P)$(R)TriggerA, $(P)$(R)TriggerA_RBV
- stringout, stringin
* - NDCircBuffTriggerB
- asynOctet
- r/w
- Name of the NDAttribute for trigger B
- CIRC_BUFF_TRIGGER_B
- $(P)$(R)TriggerB, $(P)$(R)TriggerB_RBV
- stringout, stringin
* - NDCircBuffTriggerAVal
- asynFloat64
- r/o
- Value of the NDAttribute for trigger A. The attribute defined by TriggerA must have
a numeric datatype, not string. This value field only updates when the plugin is
capturing (Capture=1).
- CIRC_BUFF_TRIGGER_A_VAL
- $(P)$(R)TriggerAVal
- ai
* - NDCircBuffTriggerBVal
- asynFloat64
- r/o
- Value of the NDAttribute for trigger B. The attribute defined by TriggerB must have
a numeric datatype, not string. This value field only updates when the plugin is
capturing (Capture=1).
- CIRC_BUFF_TRIGGER_B_VAL
- $(P)$(R)TriggerBVal
- ai
* - NDCircBuffTriggerCalc
- asynOctet
- r/w
- The calculation expression for the trigger. This can be any valid expression accepted
by the EPICS calc routines in libCom, and used for example in the EPICS calc record.
The maximum length of the expression is currently set to MAX_INFIX_SIZE (100) defined
in postfix.h in EPICS base.
- CIRC_BUFF_TRIGGER_CALC
- $(P)$(R)TriggerCalc, $(P)$(R)TriggerCalc_RBV
- waveform, waveform
* - NDCircBuffTriggerCalcVal
- asynFloat64
- r/o
- Value of the calculated expression. This value field only updates when the plugin
is capturing (Capture=1).
- CIRC_BUFF_TRIGGER_CALC_VAL
- $(P)$(R)TriggerCalcVal
- ai
* - NDCircBuffPresetTriggerCount
- asynInt32
- r/w
- Controls how many times the plugin can be triggered before capture stops. The default
is 1, so the plugin will only trigger once and then stop capturing. If this is 0
then the plugin will continue to retrigger forever until it is stopped by setting
Capture=0.
- CIRC_BUFF_PRESET_TRIGGER_COUNT
- $(P)$(R)PresetTriggerCount, $(P)$(R)PresetTriggerCount_RBV
- longout, longin
* - NDCircBuffActualTriggerCount
- asynInt32
- r/o
- The number of triggers that have occurred since capture was last started.
- CIRC_BUFF_ACTUAL_TRIGGER_COUNT
- $(P)$(R)ActualTriggerCount_RBV
- longin
* - NDCircBuffCurrentImage
- asynInt32
- r/o
- Number of NDArrays currently stored in ring buffer
- CIRC_BUFF_CURRENT_IMAGE
- $(P)$(R)CurrentQty_RBV
- longin
* - NDCircBuffPostCount
- asynInt32
- r/o
- Number of post-trigger NDArrays emitted so far
- CIRC_BUFF_POST_COUNT
- $(P)$(R)PostTriggerQty_RBV
- longin
* - NDCircBuffSoftTrigger
- asynInt32
- r/w
- Set to non-zero to force a trigger on next NDArray
- CIRC_BUFF_SOFT_TRIGGER
- $(P)$(R)Trigger
- busy
* - NDCircBuffTriggered
- asynInt32
- r/o
- Current trigger status
- CIRC_BUFF_TRIGGERED
- $(P)$(R)Trigger_RBV
- bi
* - NDCircBuffFlushOnSoftTrig
- asynInt32
- r/o
- Defines behaviour of the flush functionality. Choices are: |br|
"OnNewImage" (0, default) Flushes on new image. |br|
"Immediately" (1) Flushes immediately on software trigger.
- CIRC_BUFF_FLUSH_ON_SOFTTRIGGER
- $(P)$(R)FlushOnSoftTrg, $(P)$(R)FlushOnSoftTrg_RBV
- bo, bi
Triggering using NDArray attributes is quite powerful. Two NDArray
attributes can be used for triggering. The names of these attributes are
defined with the TriggerA and TriggerB records. The values of these
attributes must be numeric, not string. The TriggerCalc record defines a
calculation expression that uses that same syntax as the EPICS calc
record. If the expression evaluates to a non-zero value then the plugin
will be triggered. The variables in the expression are defined as
follows:
- A The current value of the NDAttribute defined by TriggerA.
- B The current value of the NDAttribute defined by TriggerB.
- C The value of the PreCount record
- D The value of the PostCount record
- E The value of the CurrentQty_RBV record
- F The value of the PostTriggerQty_RBV record
- G The value of the Trigger_RBV record
The following are some example expressions. They assume that the
NDPluginCircularBuff plugin is getting its data from the NDPluginStats
plugin and that the NDPluginStats plugin is using an attributes XML file
containing the following lines:
::
Assume that TriggerA is set to MaxValue and TriggerB is set to
CentroidX.
The following are examples of some expressions that can then be used for
triggering:
+-----------------------------------+-----------------------------------+
| Expression | Description |
+===================================+===================================+
| A<200 | Intensity of brightest pixel is |
| | less than 200 |
+-----------------------------------+-----------------------------------+
| A>1.5*H && E>50;H:=A | Intensity of brightest pixel (A) |
| | is more than 150% of the value in |
| | the previous image (H) and there |
| | are at least 50 images in the |
| | circular buffer. Set H to A after |
| | evaluation. |
+-----------------------------------+-----------------------------------+
| B<300 \|\| A>100 | X centroid is less than pixel 300 |
| | or the maximum intensity is |
| | greater than 100. |
+-----------------------------------+-----------------------------------+
If the TriggerA or TriggerB attrbutes do not exist, or if they are
non-numeric datatype then the TriggerAVal or TriggerBVal is set to NaN
(Not a Number). If that value is used in the calculation expression then
in some cases the TriggerCalcVal will also be NaN (for example A+B will
be NaN). If TriggerCalcVal is NaN or Infinity then the expression is
treated as 0 and the trigger will not occur. However, some expressions
involving NaN arguments do not result in a NaN result and could result
in false triggers. For example (A&&B) evaluates as 1 when both A and B
are NaN. To avoid this problem the ``isnan()`` and ``isinf()`` functions can be
used in the expression.
It is possible to continuously output individual NDArrays that match the
trigger condition. To do this set PreCount=0, PostCount=1, and
PresetTriggerCount=0.
Screen shots
------------
The following is the MEDM screen that provides access to the parameters
in NDPluginDriver.h and NDPluginCircularBuff.h through records in
NDPluginBase.template and NDCircularBuff.template.
.. image:: NDCircularBuff.png
:align: center
Configuration
-------------
The NDPluginCircularBuff plugin is created with the
NDCircularBuffConfigure command, either from C/C++ or from the EPICS IOC
shell.
::
NDCircularBuffConfigure(const char *portName, int queueSize, int blockingCallbacks,
const char *NDArrayPort, int NDArrayAddr,
int maxBuffers, size_t maxMemory)
For details on the meaning of the parameters to this function refer to
the detailed documentation on the NDCircularBuffConfigure function in
the `NDPluginCircularBuff.cpp
documentation <../areaDetectorDoxygenHTML/_n_d_plugin_circular_buff_8cpp.html>`__
and in the documentation for the constructor for the
`NDPluginCircularBuff
class <../areaDetectorDoxygenHTML/class_n_d_plugin_circular_buff.html>`__.
In particular, note that maxBuffers constrains the size of the ring
buffer - the plugin will discard any changes to the pre- or post count
if this would result in (pre-count + post-count) exceeding maxBuffers.