Updating Periodic Messages

While a schedule runs, the ARINC 708 data can be updated asynchronously by the main application using the mxfA708TxPeriodicUpdateMsgWrite() function.

The next example shows how to use some functions for updating a transmission buffer.

Scheduling a Message

The program below shows how to define a single message with mxfTxPeriodicScheduleSingleMsgAdd() for scheduling that will be later updated while the schedule runs.

The example in the next section shows how to update the records dynamically.

ar708_buffer_threshold.c

uint32 rc;
HMXF_SCHED schedule=0;
HMXF_SCHED_MSG msgSched;
HMXF_CHANNEL txChannel;
HMXF_BUFFER txBuffer=0;
MXF_A708_DATAREC *txHostBuffer=NULL;
size_t txBufferSize;

   ...

   // Allocates buffer for tx data
   if(!rc)
   {
      txBufferSize = 720*sizeof(MXF_A708_DATAREC);

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

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

   // Sets the Periodic Scheduler
   if(!rc)
      rc = mxfTxPeriodicScheduleNew(txChannel, &schedule);

   // Sets scheduling values: Rate=5 ms, Phase=0 us
   if(!rc)
      rc = mxfTxPeriodicScheduleSingleMsgAdd(schedule, 5000000, 0, txBuffer, &msgSched);

   // Runs the schedule
   if(!rc)
      rc = mxfTxPeriodicScheduleRun(schedule);

   // Sends messages for 2 seconds
   if(!rc)
   {
      printf("Running periodic transmission...\n\r");
      mxfSleep(2000);
      rc = mxfTxPeriodicScheduleFree(schedule);
   }

   if(txHostBuffer)
      free(txHostBuffer)

   ...

Updating the buffer

The value of the ARINC 708 data sent can be updated while a background schedule runs.

The example below shows how the mxfA708TxPeriodicUpdateMsgWrite() function can be used to perform the update operation.

The update loop changes every 5ms and stops after two seconds.

ar708_buffer_threshold.c

#define TXALMOSTFULL    100

uint32 rc=0;
uint16 i, bin;
MXF_A708_DATAREC *recPtr=txHostBuffer;
static uint32 TXAsyncEvents=0;
static uint16 scanAngle=0;
static uint16 binValue=0;

   ...

// Refills the FIFO
   for(i=0; !rc && i<TXALMOSTFULL; i++, scanAngle++)
   {
      if(scanAngle > 720)
      {
         scanAngle = 0;
         binValue++;
      }

      recPtr->timeTag=0;
      recPtr->control=0;
      recPtr->dataSize = 200;  //200 bytes corresponds to 1600 bits (see ARINC 708 specification)
      recPtr->repeatCount=1;
      recPtr->manchesterBitErr = 0;
      recPtr->data[0] = 0;
      recPtr->data[1] = 0;
      recPtr->data[2] = 0;
      recPtr->data[3] = 0;
      setLabel(recPtr, 055);       // Bits 0-7 : Label 055
      setCtrlAccept(recPtr, 0x3);   // Bits 8-9 : Cntrol Accept
      setMode(recPtr, 1);           // Mode Set 1
      setTilt(recPtr, 0);
      setGain(recPtr, -16);
      setRange(recPtr, 80);
      setDataAccept(recPtr, 3);
      setScanAngle(recPtr, ((double)scanAngle*0.25)+270);

      for(bin=1; bin<=512; bin++)
      {
         setBin(recPtr, bin, binValue);
      }

      if(!rc)
         rc = mxfA708NextDataRecordPtrGet(recPtr, &recPtr);
   }

   // Add more data to the buffer
   if(!rc)
      rc = mxfA708TxPeriodicUpdateMsgWrite(buffer, TXALMOSTFULL, txHostBuffer);

   if(rc)
      printf("Periodic Update failed; rc=0x%08x\n", rc);
   else
      printf("\nAsync Event %d - Writing %d records\n", ++TXAsyncEvents, i);


   ...