A DD Consumer Process

The following sample program is a consumer that requests all events, which have bit 3 of fev.ctlb1 set. If no event is available, the consumers returns immediately. Another consumer option is commented out: It receives only events on request, falls asleep when there are no events. In order to minimize the number of unsuccessful tries to get an event, a call to ddu_req_fev(n_events) is made. This call makes sure that always at least n_events are reserved for this process (unless data taking stopped for one reason or another).

#include <dd_user.h>

 
main(int argc,char **argv)

{

		   int *p;

		   char fname[100];

		   int mode, reqcnt, prescale, wait,ctl[4];

		   struct fifo_entry fev;

		   int go_on;

		   if (argc < 2) {

		 		     printf("syntax: argument fifo name needed \n");

		 		     exit(0);

		   }

		   strcpy(fname,argv[1]);

		   mode = FMODE_COND;

		   wait = DD_WAIT_ASYNC;

		 /* mode = FMODE_ONREQ; */

		 /* wait = DD_WAIT_SLEEP; */

		   prescale = 1;

		   ctl[0] = -1;

		   ctl[1] =  4;

		   ctl[2] = -1;

		   ctl[3] = -1;

		   if ( (status = ddu_init(fname,mode,prescale,wait,ctl)) != 0 ) {

		 		     printf("ddu_init: status returned %d\n",status);

		 		     exit(1);

		   }

		   /* if you want to have always at least 5 events */

		   /* waiting to be picked up by this process */

		   /* n_events = 5; */

		   /* ddu_set_reqcnt(n_events); */

		   ddu_start();

		   go_on = 1;

		   while (go_on & & ddu_attached() ) {

		 		     status = ddu_get_fev(&fev);

		 		     if (status == 0){

		 		 		       printf(``got an event of length %d at address %x \n'',

		 		 		 		 fev.len,fev.p2da);

		 		 		       if ( (status = ddu_put_fev(fev)) != 0 ) {

		 		 		 		 	printf("ddu_put_fev: status returned %d\n",status);

		 		 		 		 	go_on = 0;

		 		 		       }

		 		     } else if ( status < 0 ) {

		 		 		       printf("ddu_get_fev: status returned %d\n",status);

		 		 		       go_on = 0;

		 		     } else

		 		 		 	printf(``tried to get an event, but none was available\n'');

		  }

		   ddu_stop();

		   ddu_close();

		   exit(0);

}