Reading out the CAEN 32 channel VME digitizers

This section describes how to readout modules you have instantiated and initialized using CAENcard. Note that the CAEN 32 channel modules do not support channel addressability. Each module will provide 0 longwords if all channels are supressed, or between 3 and 34 longwords if at least one channel is present (n + 2 where n are the number of unsupressed channels). See page 40 of the V775 manual (e.g.) for a description of the block of data you will get from one of these modules. Note that a longword is two words.

Readout is done via the CAENcard::readEvent function. This is overloaded, but typically only two variants will be used. In the most common case, you are reading data directly to the buffer. Sample code for readout classic (or production readout if bufpt is the DAQWordBufferPtr parameter) is shown below:

        #include <CAENcard.h>
        #include <spectrodaq.h>
        #define CAENTIMEOUT 50
        ...
           CAENcard* pModule;
        ...
           for(int i =0; i < CAENTIMEOUT; i++) {
             if (pModule->dataPresent()) {
               break;
             }
           }
           if (pModule->dataPresent()) {
              pModule->readEvent(bufpt);
           }    
        ...

Note that:

1. CAENcard::dataPresent is used to determine if the card has any data to read out.
2. bufpt is passed by reference and will be modified to point to the next word after the data read by CAENcard::readEvent.
3. You should probably experimentally determine the shortest value for CAENTIMEOUT. This may be dependent on which data acquisition computer you use.

In some cases you may want to read data from the module into a local buffer and then, after some processing, copy the data you have read into the final buffer. The sample below shows how to do this.

        #include <CAENcard.h>
        #include <spectrodaq.h>
        #define CAENTIMEOUT 50
        ...
           CAENcard* pModule;
        ...
           for(int i =0; i < CAENTIMEOUT; i++) {
             if (pModule->dataPresent()) {
               break;
             }
           }
           if (pModule->dataPresent()) {
              unsigned long adcData[34];      // Temp buffer.
              int nWords = pModule->readEvent(adcData);
              int nLongs = nWords*sizeof(short)/sizeof(long);
              ..
              unsigned short* pwData = (unsigned short*)adcData;
              for(int i =0; i < nWords; i++) {
                *bufpt = *pwData++;
                ++bufpt;
              }
        ...

Note that:

1. The return value from CAENcard::readEvent is the number of words (16 bit) that were read from the device.
2. For objects, pre-increment is generally faster than postincrement because the post increment/decrement operators will require a pair of copy constructions and a destructor call, in order to preserve the semantics of post increment/decrement.

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