Transmission with Record Relative Timing

Transmission with relative record timing means the records are scheduled one after another based on the delta time tag set.

The option MXF_TXAPERIODIC_FLAG_USE_RECORD_RELATIVE_TIME is used to perform this function.

For instance, for an array of n records to transmit, the records transmit timing is as follows:

Time record 1 = record 1 time tag (offset from current time)
Time record 2 = Time record 1 + (record 2 time tag - record 1 time tag)
Time record 3 = Time record 2 + (record 3 time tag - record 2 time tag)
......
Time record n = Time record n-1 + (record n time tag - record n-1 time tag)

Each time tag becomes relative to the previous record sent.

ar708_aperiodic.c

uint32 rc;
size_t txBufferSize;
HMXF_CHANNEL txChannel;
HMXF_BUFFER txBuffer;
MXF_A708_DATAREC * txHostBuffer;
MXF_A708_DATAREC* rec;
uint32 delay100ms = 100000000;
uint64 currentTime;
uint64 data, word;

   ...


   // Allocates 4 KB buffer for tx data
   if(!rc)
   {
      txBufferSize = 4*1024;

      // Allocates TX Aperiodic static buffer for HIGH priority queue
      rc = mxfTxAperiodicBufferAlloc(txChannel, MXF_TXAPERIODIC_PRIORITY_HIGH, txBufferSize, &txBuffer, NULL);

      // Host buffer allocation
      if(!rc)
      {
         txHostBuffer = (MXF_A708_DATAREC*)calloc(1, txBufferSize);
         if(!txHostBuffer)
            rc = MAXT_ERROR_MEM;
      }
   }

   ...

   rec=txHostBuffer;

   //  In the example below the timetag in the record is set
   //  and the option MXF_TXAPERIODIC_FLAG_USE_RECORD_RELATIVE_TIME.
   //  The relative time between each records is set in the 
   //  timetag field of the record array.

   printf("\nAperiodic transmission (Record Relative)\n");

   // Set the record
      // The scheduling timetag is as follow:
      // clock current time + 100 ms
      // Each record is sent with a timetag a 5000000 nsec (5 ms) interval.

   if(!rc)
   {
      //Prepares records to send for basic transmission/reception test
      for(data=0, currentTime=100000000; data<MAX_TX_RECORDS_TO_TRANSMIT; data++)
      {
         rec->timeTag      = currentTime+(data*5000000);
         rec->control      = 0;
         rec->repeatCount  = 1;
         rec->manchesterBitErr = 0;
         rec->dataSize     = 200;  //200 bytes corresponds to 1600 bits (see ARINC 708 specification)
         for(word=0; word < rec->dataSize/2; word++)
         {
            switch(word)
            {
            case 0:
               rec->data[word] = 055; // Label 055
               break;
            case 1:
            case 2:
            case 3:
               rec->data[word] = 0x0000;
               break;
            default:
               rec->data[word] = (uint16)(0x0101*data);
            }
         }
         rc = mxfA708NextDataRecordPtrGet(rec, &rec);
      }
   }

   // Transmit the array of records
   if(!rc)
   {
      printf("Transmitting ...\n");
      rc = mxfA708TxAperiodicWrite(txBuffer, MXF_TXAPERIODIC_FLAG_USE_RECORD_RELATIVE_TIME, 0, MAX_TX_RECORDS_TO_TRANSMIT, txHostBuffer);
   }

  ...