User manual

Programmer’s Guide Page 39 of 66

long nbrSegments = 10;

long nbrPoints = 1000;

char *dataArrayP;

long currentSegmentPad;

long nbrSamplesNom, nbrSegmentsNom;

AqReadParameters *readPar = new AqReadParameters;

AqDataDescriptor *dataDesc = new AqDataDescriptor;

AqSegmentDescriptor *segDesc = new AqSegmentDescriptor[nbrSegments];

readPar->dataType = 0; // 0 = byte

readPar->readMode = 1; // 1 = sequence waveform

readPar->nbrSegments = nbrSegments;

readPar->firstSampleInSeg = 0;

readPar->segmentOffset = nbrPoints;

readPar->firstSegment = 0;

readPar->nbrSamplesInSeg = nbrPoints;

readPar->flags = 0;

readPar->reserved = 0;

readPar->reserved2 = 0.0;

readPar->reserved3 = 0.0;

status = Acqrs_getInstrumentInfo (instrID, ”TbSegmentPad”,

&currentSegmentPad);

// in this case the next call doesn‟t have any surprises

status = AcqrsD1_getMemory(instrID,

&nbrSamplesNom, &nbrSegmentsNom);

readPar->dataArraySize =

(nbrSamplesNom+currentSegmentPad)*(1+nbrSegments);

// here we show the malloc explicitly

dataArrayP = (char *)malloc(readPar->dataArraySize);

readPar->segDescArraySize = sizeof(AqSegmentDescriptor)*nbrSegments;

status = AcqrsD1_readData(instrID, channel, readPar, dataArrayP,

dataDesc, segDesc);

Comments:

 The explicit malloc call will normally not be repeated for every acquisition. Obviously, a larger than needed

allocation is perfectly acceptable. Also, any space allocated this way ought to be returned to the heap at

some point.

 It is possible to allocate dataArray space that is not aligned on a 32-bit boundary. This is not acceptable for

some of our modules and the AcqrsD1_readData routine will return an error in such a case.

3.11.3. Reading Raw Sequences of Waveforms

In the example given above the driver software in the PC does the work of reordering the raw data sent by the

digitizer so that it can be conveniently used from the dataArrayP vector. Readout time can be slightly reduced even

further by postponing the reorder until later at a less time critical moment. This functionality is offered with the

readMode = 11, raw sequence waveform read. The segment descriptor is modified to include the information needed

by the user to the post-acquisition reordering; this requires more space. The dataArray storage space requirements are

the same as for readMode = 11. A typical piece of code to do the reorder could look as follows: