Transferring partial records Sample Clauses

Transferring partial records. AlazarRead can transfer a segment of a record from on-board memory to a buffer in host memory. This may be useful if: • The number of bytes in a full record in on-board memory exceeds the buffer size in bytes that an application can allocate in host memory. • An application wishes to reduce the time required for data transfer when it acquires relatively long records to on-board memory, but is only interested in a relatively small part of the record. Use the “TransferOffset” parameter in the call to AlazarRead to specify the offset, in samples from the trigger position in the record, of the first sample to transfer from on- board memory to the application buffer. And use the “TransferLength” parameter to specify the number of samples to transfer from on-board memory to the application buffer, where this number of samples may be less than the number of samples per record. The following code fragment divides a record into segments, and transfers the segments from on-board to host memory. // Allocate a buffer to hold one record segment. // Note that the buffer must be at least 16 samples // larger than the number of samples per buffer. U32 allocBytes = bytesPerSample * (samplesPerBuffer + 16); void* buffer = malloc(allocBytes); // Transfer a record in segments from on-board memory U32 samplesToRead = samplesPerRecord; long triggerOffset_samples = -(long)preTriggerSamples; while (samplesToRead > 0) { // Transfer a record segment from on-board memory U32 samplesThisRead; if (samplesToRead > samplesPerBuffer) samplesThisRead = samplesPerBuffer; else samplesThisRead = samplesToRead; AlazarRead ( boardHandle, // HANDLE -- board handle CHANNEL_A, // U32 -- channel Id buffer, // void* -- buffer bytesPerSample, // int -- bytes per sample (long) record, // long -- record (1 indexed) triggerOffset_samples, // long -- trigger offset samplesThisRead // U32 -- samples to transfer ); // Process the record segment here WriteSamplesToFile(buffer, samplesThisRead); // Point to next record segment in on-board memory triggerOffset_samples += samplesThisRead; // Decrement number of samples left to read samplesToRead -= samplesThisRead; } See “%ATS_SDK_DIR%\Samples\SinglePort\AR_Segments” for a complete sample program that demonstrates how to read records in segments.