areaDetector Eiger driver

Table of Contents

• Introduction
• Trigger Modes
• Manual Trigger
• Data Acquisition
  • Using FileWriter
  • Using Stream
  • Using Monitor
• Implementation of standard driver parameters
• Eiger specific parameters
• Unsupported standard driver parameters
• Configuration
• CSS screen
• Known Issues
  • Changing the Photon Energy
  • Status Parameters Polling
  • Internal Enable Mode

Introduction

This is an EPICS areaDetector driver for the Eiger detector from Dectris. It has been tested on the Eiger 500K, 1M, 4M and 16M with the firmware version 1.6.4+. The driver communicates with the detector via its SIMPLON REST interface, so no library from Dectris is required. The images can pulled from the detector as HDF5 files, as a ZeroMQ stream or both. The files can be both saved to disk and passed to the areaDetector pipeline at the same time.

All trigger modes are supported, although Internal Enable mode seems to not be working properly. See Known Issues.

This driver inherits from ADDriver. It implements many of the parameters in asynNDArrayDriver.h and in ADArrayDriver.h. It also implements a number of parameters that are specific to the Eiger detector. The eigerDetector class documentation describes this class in detail.

This document does not attempt to explain the meaning of the Eiger-specific parameters, as they are explained in the SIMPLON API Reference and in the EIGER Detector Manual documents from Dectris. Sometimes it does, however, refer to those parameters as they are named in Dectris' documentation.

The SIMPLON API provides ways to query parameter limits, valid values for enums, error conditions, etc. The driver will clamp values to their minumum or maximum value if they are outside the acceptable range. Setting a parameter will immediately push its value to the detector.

This driver was built upon a multithreaded architecture. A combination of threads is used to simultaneously pull files from the detector, save them to disk and parse them into NDArrays. A dedicated thread is used to receive images in a ZeroMQ stream.

A few Eiger parameters are set at IOC initialization time and are expected to not change. Namely:

• detector/config/auto_summation = true
• filewriter/config/image_nr_start = 1
• monitor/config/buffer_size = 1

Accessing New Parameters

Some parameters are not relevant to the driver operation and as such are not exposed initially by the driver as PVs. However, there is a mechanism to access other parameters not created automatically by the driver by simply instantiating new records with the appropriate drvInfo string. Some of the PVs are created this way. For example, the PV XPixelSize_RBV has the following drvInfo:

EIG_DCD_x_pixel_size

For those parameters, the first four characters must be EIG_. Then the fifth character must be one of:

• D: Detector subsystem
• M: Monitor subsystem
• F: FileWriter subsystem
• S: Stream subsystem

The sixth character determines if the parameter is a configuration or a status parameter:

• C: Configuration
• S: Status

The seventh character determines which asyn parameter type to use:

• I: Integer (asynParamInt32)
• D: Double (asynParamFloat64)
• S: String (asynParamOctet)

The eighth character must be a _, and the remaining characters are the parameter's name according to the SIMPLON API Manual. Hence, for this example, this PV will be accessing the parameter:

detector/api/<version>/config/x_pixel_size

Trigger Modes

There are four trigger modes available:

• Internal Series: one internal trigger pulse generates N images
• Internal Enable: one internal trigger pulse generates one image
• External Series: one external trigger pulse generates N images
• External Enable: one external trigger pulse generates one image

The total number of images generated by Internal and External Series modes is given by the product of the NumImages and NumTriggers PVs (nimages and ntriggers in Dectris terminology).

On both Internal and External Enable modes the total number of images generated is given solely by the NumTriggers PV (ntriggers). NumImages is set to 1 temporarily during the acquisition.

Triggers for Internal Enable mode are sent by processing the Trigger PV. The exposure for each individual image is given by the TriggerExposure PV and can change between triggers in the same acquisition. This mode is experimental as of firmware 1.5.0. See Known Issues.

Manual Trigger

On Internal Series and Internal Enable modes, if the ManualTrigger PV is set to YES, the triggers are not auto generated by the driver. Instead, they are sent by processing the Trigger PV. On Internal Enable mode the trigger carries an exposure value that can change for each trigger, which is set by the TriggerExposure PV. Note that the Internal Enable mode is experimental as of firmware 1.5.0, see Known Issues.

Data Acquisition

Data generated by the Eiger can be pulled from the detector in a number of ways. The detector has three modules (in Dectris' terminology) that make the results of the acquisition available in different ways. The FileWriter module writes the generated images to the detector disk as HDF5 files that consist of a master (header) file and a number of data files. The Stream module makes the images available as soon as they are captured as a ZeroMQ stream. The Monitor module produces TIFF images every so often to monitor how a long acquisition is progressing.

Data from the FileWriter or from the Stream mode can be parsed into NDArrays for the areaDetector pipeline. The actual source is selected with the DataSource PV. If DataSource is set to None, however, no data will be sent to the areaDetector pipeline but the detector will still be controllable via the areaDetector driver; third-party clients can then pull files or listen to the ZeroMQ stream independently of this driver.

Using FileWriter

The FileWriter module is activated when FWEnable is set to Yes. Files generated by the FileWriter have names according to the FWNamePattern PV. The default pattern is "series_$id", where $id is replaced by the Sequence ID of the acquisition. A master file is generated as soon as the detector is successfully armed. A number of data files follow. The number of data files generated depends on the total number of images of the acquisition and the FWNFilesPerImage PV.

For example, if TriggerMode is External Enable, NumImages is 60, NumTriggers is 2, FWNImagesPerFile is 100, Sequence ID for the acquisition is 1 and FWNamePattern is "series_$id", a total of three files will be generated:

• series_1_master.h5
• series_1_data_000001.h5 (with 100 images)
• series_1_data_000002.h5 (with 20 images)

The generated files will be downloaded either if DataSource is set to FileWriter or if SaveFiles is set to Yes. Files are downloaded as soon as they are available. To determine if a file is available the driver polls the detector at a nominal rate of 10Hz. While a file is being processed the next file available is downloaded in parallel. All files will remain on the detector disk unless FWAutoRemove is set to Yes.

When saving files to disk (SaveFiles = Yes) it is possible to set the file's owner, its group and its access permissions with FileOwner, FileOwnerGrp and FilePerms PVs. To be able to set arbitrary owners the IOC executable requires CAP_SETUID and CAP_SETGID capabilities, which can be given with the command:

sudo setcap cap_setuid,cap_setgid+ep eigerDetectorApp

All files on the detector disk can be deleted at once by processing the FWClear PV.

If the last data file of a series won't be full (e.g. series_1_data_000002.h5 with 20 images) then it will only appear on the detector disk after a disarm command (issued when the acquisition is stopped), which flushes the FileWriter buffer.

Using Stream

The Stream module is activated when StreamEnable is set to Yes. Data will then be available on the detector's tcp port 9999 as a ZMQ_PUSH socket. If DataSource is set to Stream, this driver opens a corresponding ZMQ_PULL socket and parses the incoming data as NDArrays. Otherwise a third-party client can listen on that socket for data. The format of the packets is specified in the Eiger SIMPLON API documentation.

Using Monitor

The Monitor module is activated when MonitorEnable is set to Yes. Data will be available whenever the monitor module buffer is full (has one image available). This driver waits MonitorTimeout ms for data to be available. There is a rate-limit of 10Hz. Once downloaded, the TIFF image is parsed into areaDetector's NDArray on NDArrayAddr 1 (therefore, an independent NDArray stream).

Chrystallography Parameters

A few parameters are available as metadata for the acquisition. These values are stored on the master file and sent as metadata in ZeroMQ stream, but otherwise don't affect the acquisition, with the exception of the Wavelength parameter, which sets Photon Energy accordingly.

Implementation of standard driver parameters

The following table describes how the Eiger driver implements some of the standard driver parameters.

Eiger specific parameters

The Eiger driver implements the following parameters in addition to those in asynNDArrayDriver.h and ADDriver.h.

Unsupported standard driver parameters

All standard parameters not mentioned in this document are not supported.

Configuration

The Eiger driver is created with the eigerDetectorConfig command, either from C/C++ or from the EPICS IOC shell.

int eigerDetectorConfig(const char *portName, const char *hostname,
                  int maxBuffers, size_t maxMemory, int priority, int stackSize)
    

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

There an example IOC boot directory and startup script provided with areaDetector.

medm screen

The following shows the medm screen that is used to control the Eiger detector. Note that the general purpose screen ADBase.adl can be used, but it exposes a few controls that are not applicable to the Eiger, and lacks some fields that are important for the Eiger.

eigerDetector.adl is the screen used to control the Eiger driver.

eigerDetector,\adl

Known Issues

Changing the Photon Energy

Changing the Photon Energy is a potentially slow operation, depending on the detector size. On the 16M it takes around ten seconds. Other parameters also take this long because they also affect the Photon Energy, namely Threshold Energy and Wavelength. The StatusMessage PV indicates when setting any of these parameters start and finish.

Status Parameters Polling

A few status parameters are read every time the ReadStatus PV is processed. A high rate polling causes issues, sometimes causing the detector to hang when, in conjunction, a parameter is set to an invalid value.

Internal Enable Mode

The Internal Enable mode is marked as experimental by Dectris. At the moment it is very flaky (firmware 1.5.0) and often doesn't generate all the files it is supposed to.