[subexp-daq] Question on JSON output from UCESB: handling of DATA12_OVERFLOW

[Weber, Guenter Dr.]

Dear friends,


were found some unexpected (at least to us) behaviour when looking at the JSON output from UCESB.


We are using the following command to generate the JSON outout:


../../ucesb/jena_polarimeter/jena_polarimeter stream://localhost:8003 --ntuple=UNPACK,STRUCT,- | ../../ucesb/hbook/struct_writer - --dump=compact_json


In our DAQ, there are sitting CAEN V785 modules. The *.spec file for these modules looks like this:


#define VME_CAEN_V792 VME_CAEN_V775
#define VME_CAEN_V785 VME_CAEN_V775

VME_CAEN_V775(geom,
          crate)
{
  MEMBER(DATA12_OVERFLOW data[32] ZERO_SUPPRESS);

  UINT32 header NOENCODE
    {
      // 0_7: undefined;
      8_13:  count;
      16_23: crate = MATCH(crate);
      24_26: 0b010;
      27_31: geom = MATCH(geom);
    }

  list(0<=index<header.count)
    {
      UINT32 ch_data NOENCODE
    {
      0_11:  value;

      12:    overflow;
      13:    underflow;
      14:    valid;

      // 15: undefined;

      16_20: channel;

      24_26: 0b000;
      27_31: geom = CHECK(geom);

      ENCODE(data[channel],(value=value,overflow=overflow));
    }
    }

  UINT32 eob
    {
      0_23:  event_number;
      24_26: 0b100;
      27_31: geom = CHECK(geom);
      // NOENCODE;
    }
}


Now comes the strange part: from time to time we get values greater than 2^12 in the arrays belonging to the 12-bit ADC data (the values are than usually in the 36xxx ballpark). We assume that these are the overflow events and for some reason they are translated to values of 2^15 + something in the JSON output data.


Is our interprtation correct and if yes, is this intended behaviour?




Many thanks!




Best greetings

Günter



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