Acquisition with Trigger

A basic acquisition program allows capturing all data received on a bus. In some cases, it is necessary to start capturing the traffic only when a specific event is detected. In this case, the acquisition triggering service can be used. Two types of events are supported: trigger on a specific ARINC 429 data word content and trigger on the running state of another channel.

When an acquisition with trigger is started, the received data is not available to the application until the trigger condition(s) are met. In this state, the data received is kept in a circular queue. The maximum number of data records to be kept in the queue is configurable. If the queue is full, the older data is flushed to make place for newly incoming data. When the trigger conditions are realized, the acquisition goes into a running state. In this state, the pre-trig data and all newly incoming data are queued until the application reads them (through the mxfA429RxAcqRead() function).
Trigger conditions can be "ANDed" or "ORed" together.

Acquisition Trigger Service

The following functions are defined for the trigger service:

• mxfRxAcqTrigConditionListAlloc()
• mxfRxAcqTrigConditionListFree()
• mxfRxAcqTrigConditionListExprSet()
• mxfRxAcqTrigConditionAdd()
• mxfRxAcqTrigTimeGet()
• mxfRxAcqTrigSet()

Example

ar429_rx_acquisition_trigger.c
In the example below, an extra triggering logic has been added to the initialization of the code of the previous basic acquisition example to show how triggering on a specific data word content can be set.

#define LABEL                 7
#define SDI                   0

HMXF_SERVER  server;
HMXF_BUFFER  rxBuffer;
MXF_RXACQ_TRIG_COND_RDATA_DW_PARM condParam;
HMXF_COND_LIST condList=0;
uint64 status, trigTime=0;
time_t timeTemp;
struct tm * ptm;
char szTime[1024];
uint64 msec, usec;

   ...

   // Sets timebase to computer time 64-bit microseconds
   if (!rc)
      rc = mxfSystemTimeBaseSet(server, MXF_TIMEBASE_COMPUTER_USEC);

   // Configures trigger
   // Creates the condition list
   if (!rc)
      rc = mxfRxAcqTrigConditionListAlloc(server, &condList);

   // The condition will be triggered on bit 10 value of LABEL/SDI
   if(!rc)
   {
      condParam.mask = 0x000007ff;
      condParam.data = (1 << 10) | (SDI << 8) | LABEL;
      condParam.offset = 0;
      condParam.options = MXF_RXACQ_TRIG_COND_RDATA_OPTIONS_EQUAL;

      rc = mxfRxAcqTrigConditionAdd(condList, MXF_RXACQ_TRIG_COND_ID_RDATA_DW , &condParam);
   }

   // Sets the trigger with a pretrig count of 3 which allows some records to be read before the condition was triggered.
   // For the A429 protocol this number is rounded to the closest internal acquisition buffer size.
   if(!rc)
      rc = mxfRxAcqTrigSet(rxBuffer, condList, 3);

   ...

   // Checks trigger happened
   if(!rc)
      rc = mxfRxAcqBufferStatusGet(rxBuffer, &status, NULL, NULL, NULL);
   if(!rc)
   {
      if(status & MXF_RXACQ_STATUS_TRIG_OCCURRED)
      {
         // Displays the acquisition trigger time
         rc = mxfRxAcqTrigTimeGet(rxBuffer, &trigTime);
         if(!rc)
         {
            timeTemp = trigTime/1000000;
            ptm = localtime(&timeTemp);
            strftime(szTime, sizeof(szTime), "%Y-%m-%d %H:%M:%S", ptm);
            usec = trigTime%1000;
            timeTemp = trigTime/1000;
            msec = timeTemp%1000;
            printf("Event triggered at %s:%03llu:%03llu\n", szTime, msec, usec);
         }
      }
      else
         printf("Trigger not fired\n");
   }

   ...