Sending Periodic Messages

The basic logic to send periodic messages is as follows:

• First, create a schedule instance for a given channel using mxfTxPeriodicScheduleNew().
• Before adding the ARINC 708 records to the message, at least one buffer list must be added with mxfTxPeriodicScheduleBufferListAdd(). The function includes an argument to specify how many buffers (ARINC 708 data) the list will contain. If the list includes more than one buffer, one ARINC 708 record for each buffer included in the list will be sent back-to-back at the message update rate.
• Many buffer lists can be added to a message if desired. The function mxfTxPeriodicScheduleBufferListAdd() includes an argument to specify a time delay to be inserted between two consecutive buffer lists.
• Set the ARINC 708 data in the MXF_A708_DATAREC for a given record using mxfA708TxPeriodicUpdateMsgWrite().
• Start the schedule using mxfTxPeriodicScheduleRun().

The example below illustrates how to put it together:

ar708_periodic.c

#define BUFFER_SIZE     4096 // 4KB

uint32 rc;
HMXF_CHANNEL txChannel;
HMXF_BUFFER txBuffer;
MXF_A708_DATAREC* rec;
MXF_A708_DATAREC* txHostBuffer;
HMXF_SCHED schedule;
HMXF_SCHED_MSG msg=0;
uint64 data, word;

   ...

   // Set timebase to 64-bit microseconds
   if (!rc)
      rc = mxfSystemTimeBaseSet(server, MXF_TIMEBASE_DEVICE_USEC);

   // Allocate TX Periodic Update buffer
   if(!rc)
      rc = mxfTxPeriodicUpdateMsgBufferAlloc(txChannel, 0, BUFFER_SIZE, &txBuffer, NULL);

   // Allocate host buffer
   if (!rc)
   {
      txHostBuffer = (MXF_A708_DATAREC*)malloc(BUFFER_SIZE);
      if (!txHostBuffer)
         rc = MAXT_ERROR_MEM;
   }

   // Create the periodic scheduler
   rc = mxfTxPeriodicScheduleNew(txChannel, &schedule);

   // Set scheduling values: Rate=5 ms, Phase=0 us
   if(!rc)
      rc = mxfTxPeriodicScheduleMsgAdd(schedule, 5000, 0, &msg);

   // Define the number of buffer for the list and link to it
   if(!rc)
      rc = mxfTxPeriodicScheduleBufferListAdd(msg, 1, 0, txBuffer);

   // Set records for the buffers
   if(!rc)
   {
      rec = txHostBuffer;
      //Prepares records to send for basic transmission/reception test
      for(data=0; data<MAX_TX_RECORDS_TO_TRANSMIT; data++)
      {
         rec->timeTag      = 0;
         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++)     //The first 8 bits of each message have to be 0xB4
         {
            switch(word)
            {
            case 0:
               rec->data[word] = 055;
               break;
            case 1:
            case 2:
            case 3:
            case 4:
               rec->data[word] = 0x0000;
               break;
            default:
              rec->data[word] = (uint16)(0x0101*data);
            }
         }
         rc = mxfA708NextDataRecordPtrGet(rec, &rec);
      }
   }

   if (!rc)
      rc = mxfA708TxPeriodicUpdateMsgWrite(*txBuffer, MAX_TX_RECORDS_TO_TRANSMIT, txHostBuffer);

   //  Run the scheduler, update records
   if(!rc)
   {
      printf("Running periodic transmission, please wait...\n\r");

      // Run the schedule now
      rc = mxfTxPeriodicScheduleRun(schedule);
   }

   // Wait 1 second
   if(!rc)
   {
      mxfSleep(1000);

      rc = mxfTxPeriodicScheduleFree(schedule);
   }

  ...