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    User name R. Michaels

    Log entry time 15:07:51 on July 30, 2010

    Entry number 331669

    Followups:

    keyword=Qweak helicity into datastream. Looks good.

    The helicity signals were routed to the L-HRS and plugged in.
    See hallaweb.jlab.org/equipment/daq/qweak_helicity.html.
    
    The scaler was put into FIFO mode and reads the data at the helicity
    flip rate.  At present this rate is 1 kHz with free-running clock,
    with a Quartet pattern and delay by 8 windows -- which will be
    normal during Qweak.
    
    The scaler readout works with zero deadtime.  The measured helicity
    is checked versus predicted helicity using the new 30-bit predictor
    algorithm from Riad Suleiman et.al. 
    
    If something goes wrong, e.g. you unplug the helicity signal, you get
    warnings like this at the vxWorks prompt for TS11:
    
    0x1ea952a0 (SISProd): ERROR in predicted helicity. You are losing data !
    
    Of course, nothing usually goes wrong !  
    
    There's still a bit of work to finish this project: some new software
    for Podd, and to build in some redundancy like reading bits with ADCs.
    
    Below are some typical data.  Qrt=1 denotes the start of a Quartet,
    and you can see the correct pattern of helicity bits:
    
    ----------  Typical helicity data ---------------
    
      qrt  1    hel 1    
      qrt  0    hel 0    
      qrt  0    hel 0    
      qrt  0    hel 1    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 1    
      qrt  0    hel 0    
      qrt  0    hel 0    
      qrt  0    hel 1    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
      qrt  1    hel 0    
      qrt  0    hel 1    
      qrt  0    hel 1    
      qrt  0    hel 0    
    
    


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