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Message ID: 767     Entry time: 21 Jun 2011
Author: Stefan Ritt 
Topic: Info 
Subject: New MIDAS sequencer 
A new sequencer for starting and stopping runs has been implemented. Although it is till kind of in a preliminary phase, it is usable, so I would like to share the syntax with you.

The sequencer runs inside mhttpd, and creates a new ODB subdirectory "/Sequencer". There is a new button on the status page called "Sequencer". In can run scripts in XML format, which reside on the server (where mhttpd is running). The sequencer is stateless, that means even if mhttpd is stopped and restarted, it resumes operation from where it has been stopped. Following statements are implemented:

  • <Comment>comment</Comment>
    a comment for this XML file, for information only

  • <ODBSet path="path">value</ODBSet>
    to set a value in the ODB

  • <ODBInc path="path">delta</ODBInc>
    to increment a value in the ODB

  • <RunDescription>Description</RunDescription>
    a run description which is stored under /Experiment/Run Parameters/Run Description.

  • <Transition>Start | Stop</Transition>
    to start or stop a run

  • <Loop n="n"> ... </Loop>
    to execute a loop n times. For infinite loops, "infinit" can be specified as n

  • <Wait for="events | ODBvalue | seconds" [path="ODB path"]>x</Wait>
    wait until a number of events is acquired (testing /Equipment/Trigger/Statistics/Events sent), or until a value in the ODB exceeds x, or wait for x seconds.

  • <Script [loop_counter="1"]>Script</Script>
    to call a script on the server side. Optionally, the loop counter(s) are passed to the script

Attached is a simple script which can be used as a starting point.
Attachment 1: seqtest.xml  698 Bytes  | Hide | Hide all
<?xml version="1.0" encoding="ISO-8859-1"?>
<RunSequence xmlns:xsi="" xsi:noNamespaceSchemaLocation="">
<Comment>This is the XML test file</Comment>

<ODBSet path="/Experiment/Run Parameters/Comment">Test comment</ODBSet>
<RunDescription>Test Run</RunDescription>

<!-- do 10 runs -->
<Loop n="10">
   <!-- increment high voltage and wait for some time to settle -->
   <ODBInc path="/Equipment/HV/Variables/Demand[0]">10</ODBInc>
   <Wait for="seconds">10</Wait>

   <!-- start a run, acquire 3000 events -->
   <Wait for="events">3000</Wait>
   <Transition>Stop</Transition> -->
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