Re: Request: Survey of EPICS PVA ( a.k.a EPICS V4) users

[Mark Rivers <rivers@cars.uchicago.edu>]

Hi Ernest,


I think one of the most common use-cases for PVA is the NDPluginPva and the ImageJ EPICS_NTNDA_Viewer.java.  We are already using this on some of our areaDetector IOCS on beamlines at the APS.  We are currently using base 3.15.5 and the unbundled EPICS-CPP-4.6.0 package.  However, on my development machines I am using EPICS 7.0.1 and I may deploy this on all of our production IOCs during the current APS shutdown.  The advantages of PVA versus CA for this application are:

  *   The NTNDArray data is transmitted "atomically" over the network, rather than using separate PVs for the image data and the metadata (image dimensions, color mode, etc.)
  *   When using Channel Access the data type of the waveform record is fixed at iocInit, and cannot be changed at runtime. This means, for example, that if the user might want to view both 8-bit images, 16-bit images, and 64-bit double FFT images then the waveform record would need to be 64-bit double, which adds a factor of 8 network overhead when viewing 8-bit images. pvAccess changes the data type of the NTNDArrays dynamically at run-time, removing this restriction.
  *   Channel Access requires setting EPICS_CA_MAX_ARRAY_BYTES, which is a source of considerable confusion and frustration for users. pvAccess does not use EPICS_CA_MAX_ARRAY_BYTES and there is no restriction on the size of the NTNDArrays.
  *   The performance using pvAccess is significantly better than using Channel Access. NDPluginPva is 5-10 times faster than NDPluginStdArrays, and ImageJ can display 1.5-2 times more images/s with pvAccess than with Channel Access.


I did discover a problem with the recDynLink code in the calc module this week which would cause problems with swait and sscan records.  But Andrew has fixed that problem in the master branch of calc on Github.  People need to start using EPICS 7 in earnest so we can find all the bugs like this.


Mark


________________________________
From: tech-talk-bounces@aps.anl.gov <tech-talk-bounces@aps.anl.gov> on behalf of Williams Jr., Ernest L. <ernesto@slac.stanford.edu>
Sent: Wednesday, May 2, 2018 7:17 PM
To: tech-talk@aps.anl.gov
Subject: Request: Survey of EPICS PVA ( a.k.a EPICS V4) users


Hi everyone,


For our controls software development and deployment road map here at SLAC; we are pursuing EPICS PVA and EPICS 7.


I would like to ask if other facilities in our EPICS community are also investing/pursuing EPICS PVA?


Thanks in advance for your response and feedback.




Cheers,

Ernest Williams