Sampling Service

The sampling service is useful when not all the traffic needs to be captured, but only a snapshot (for display for example). The sampling logic keeps the last ARINC 708 record received for each label. The service also allows the discarding of the latest data from the queue if it becomes obsolete after a period of time called, kill time.

The way to setup a basic sampling receive application is as follows:

• A receive channel must be obtained using the mxfModuleChannelGet() or mxfModuleChannelAllGet() functions using MXF_SCLASS_RXSAMPLING_SRV subclass.
• The Sampling buffer must be allocated using the mxfRxSamplingBufferAlloc() function.
• A sampling kill time can be set with the mxfRxSamplingKilltimeSet() function to allow the invalidation of the last reception if the data is too old.
• Start the sampling using the mxfRxSamplingStart() function.
• Sampling read can be performed by using the mxfA708RxSamplingRead() or mxfA708RxSamplingSingleRead() functions.

The MXF_A708_SAMPREC structure must be used for reading a ARINC 708 message with the sampling service.

Example

ar708_sampling.c

#define MAX_TX_RECORDS_TO_TRANSMIT     10
#define BUFFER_SIZE  MAX_TX_RECORDS_TO_TRANSMIT*sizeof(MXF_A708_DATAREC)

HMXF_SERVER  server;
HMXF_CHANNEL rxChannel;
HMXF_BUFFER  rxBuffer;
MXF_A708_SAMPREC* hostBuffer=NULL;
uint32 rc;
uint64 i, msgsCount, bytesCount;

   ...

   // Sets timebase to RTC usec
   if(!rc)
      rc = mxfSystemTimeBaseSet(server, MXF_TIMEBASE_DEVICE_USEC);

   // Allocate RX sampling buffer
   if(!rc)
      rc = mxfRxSamplingBufferAlloc(rxChannel, BUFFER_SIZE, &rxBuffer, NULL);

   // Sets sampling kill time to 5 seconds.
   if (!rc)
      rc = mxfRxSamplingKilltimeSet(rxBuffer, 5000000);

   // Start sampling
   if(!rc)
      rc = mxfRxSamplingStart(rxBuffer);

   if(!rc)
      printf("Sampling started\n\r");

   ...

   // Read and display records for 5 seconds
   for(i=0; i<10 && !rc; i++)
   {
      rc = mxfA708RxSamplingRead(rxBuffer, MXF_RXSAMPLING_FLAG_DEFAULT, 0, BUFFER_SIZE, &msgsCount, &bytesCount, hostBuffer);
      if(!rc)
      {
      uint64 iRec,
             iData;
      MXF_A708_SAMPREC *p=hostBuffer;

         printf("Read %llu messages\n\r", msgsCount);

         printf("\n");
         for(iRec=0; iRec < msgsCount; iRec++)
         {
            printf("%03llu %010llu 0x%08x %02u ",  iRec, p->timeTag, p->control, p->dataSize);

            for(iData=0; iData < p->dataSize/2; iData++)
            {
               printf("%04x ", p->data[iData]);

               if(!((iData+1)%8) && (iData+1 < p->dataSize/2))
                  printf("\n                              ");
            }
            printf("\n");

            mxfA708NextSamplingRecordPtrGet(p, &p);
         }
      }

      if(rc)
         printf("Sampling read failed; rc=0x%08x\n", rc);
      else
         mxfSleep(500);
   }

   // Stop sampling
   if(!rc)
      rc = mxfRxSamplingStop(rxBuffer);

   ...