Versions Compared

Old Version 29

changes.mady.by.user Christopher O'Grady

Saved on

compared with

New Version 30

changes.mady.by.user Unknown User (davidsch)

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

Note
titleHow to properly use the EPICS store

It's important to understand that the contents of the store is relevant to the most recent event obtained from a data set. This means that:

  • the store will be empty contain the configuration pv's after a data set has been just open opened and no single event has been fetched from it
  • the contents of the store will change from one event to the other one

Therefore it's up to a user code to implement a correct logic for fetching events and EPICS variables to ensure that they're properly synchronized.

...

Code Block
bgColor#F7F7ED
ds = DataSource(dsname)
epics = ds.env().epicsStore()
prev_val = None
for i, evt in enumerate(ds.events()):
    val = epics.value('LAS:FS0:ACOU:amp_rf1_17_2:rd')
    if val != prev_val:
        print "%6d:" % i, val
        prev_val = val
 

     0: 2016
   725: 2024
   845: 2019
   966: 2014
  1932: 2021
  2053: 2020
  2174: 2016
  3381: 2020
  3502: 2024
  4830: 2018
  6279: 2019
  6400: 2018
  7728: 2023
  7849: 2019
  9177: 2016
 10626: 2021
 10747: 2022
 12075: 2016
 13524: 2020
 ..

Configuration pv's refer to EPIC's ctrl headers. These are not often used for analysis and all EPICS pv's should be replaced by event data after the first event is fetched. However we have seen a few cases where a ctrl pv was not replaced immediately. These issues have been resolved for future runs, but to be careful, one could rewrite the main loop as follows:

Code Block
languagepython
for i, evt in enumerate(ds.events()):
    pv = epics.getPV('LAS:FS0:ACOU:amp_rf1_17_2:rd')
    if pv.isCtrl():
        print "warning: pv is still ctrl as of event %d, may be known or new bug" % i
        continue
    val = pv.value(0)

Services

The Histogram Manager is the only public (user-level) service which is implemented in the current version of the framework. A reference to the manager can be obtain using:

...

Info
titleWhere can I find a list of existing *psana* modules?

There are two documents which you may want to explore:

Anchor
cspad
cspad

...