Control System Studio (CSS) Data Access Layer (DAL)

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Control System Studio (CSS) Data Access Layer
(DAL)

• Kay Kasemir, Xihui Chen
• kasemirk_at_ornl.gov
• July 2009

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Data Access Layer (DAL)

• Proposed by DESY, implemented by Cosylab, around
  2006
• Idea Support
• EPICS Channel Access, TINE, TANGO, Doocs, new
  protocols
• Wide as well as Narrow API
• Magnet.getCurrent() as well as Channel.getProperty
  (current)
• Basic read/write as well as remote commands
• CSS adds a Simple-DAL layer

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(Simple-)DAL PV Names

• system/device/propertycharacteristic, type
• Systems EPICS, Simulated, Local PVs, some TINE
• For EPICS
• System epics
• Device empty since EPICS lacks device hierarchy
• Property EPICS Channel name
• Characteristic EPICS Channel Property
• Type String, Double,
• No commands
• Examples
• epics//some_recordvalue
• epics//some_recordseverity
• epics//some_recordwarningMin
• epics//some_recordunits epics//some_record
  .EGUvalue

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DAL Issues

• ConfusingDAL Property EPICS Channel,DAL
  Characteristic EPICS Property
• syntax for characteristics unfortunate for
  future array access support
• Time stamp detail was only seconds (fixed, now
  nanosecs)
• severity was missing (fixed)
• Channel Access was locked to CAJ, no JNI (fixed?)

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DAL API

• Only basic Java types, locked at time of
  subscription
• For enumerated type, SDS user has to enter PV as
  epics//.., String
• Event API
• void valueChanged(E value, Timestamp timestamp)
• PV data type locked at compile time, or just
  Object
• No PV parameter that would allow use of same
  listener for multiple PVs
• Clients like strip chart, archiver, alarm
  handler, basically need
  epics//some_pvvalue, status, severitybut have
  to use separate PVs for each characteristic

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PV API

• Developed in late 2006 because DAL wasnt usable
  at that time
• Close to EPICS
• Listener receives updates with PV, Value
• Value is
• scalar or array of String, Double, Integer
• Time, Severity, Status
• Numeric (units, precision, display alarm
  limits) or Enumeration Meta Data (states)
• Implementations
• ca// Channel Access, JCA or CAJ
• loc// Local PVs
• sim// Simulated ramp, sine, noise
• sys// System PVs (user name, free memory, )

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Summary

• CSS has two extensible PV layers
• Both implemented for EPICS, simulated, local,
  system PVs
• PV is simpler, maybe too EPICS specific
• DAL is meant to support anything
• DAL Users (via SimpleDAL layer)
• Synoptic Display, maybe other Cosylab uses
  outside of CSS (GSI Demo)
• PV Users
• Probe, Data Browser, PACE, PV Table, PV Tree, PV
  Field Viewer, BEAUTY, BEAST
• Future
• Add features to PV, so it turns into
  almost-simple-DAL, then merge?
• Fix issues in DAL, then use it everywhere?