using IIR filter library for C2000 DSP

Hi,
   I wanna implement a low pass IIR filter in C2407 using the 24x
Filter library.
   I am a new comer to this kind of implementation.

    /*After the initation:*/
   {
    iir.dbuffer_ptr=dbuffer;
    iir.coeff_ptr=coeff;
    iir.qfmat=IIR_LPF_QFMAT;
    iir.nbiq=IIR_LPF_NBIQ;
    iir.isf=IIR_LPF_ISF;
    iir.init(&iir);
   }

   while(ADUPDATE)  /*new adc coming*/
   {

         iir.input=xn;     /*new value into delay buffer*/

          iir.calc(&iir);                              /*fir
calculation*/
          yn=(iir.output<<1);
         ADUPDATE=0;

   }


I met some problem i can not explain.
  1)  If I directly set xn=100, I found yn is always be zero.
  2)  if I set xn=8005, then , yn=7896
           set  xn=2048, then, yn= 969
                 xn=4096, yn= 1968
                  xn=8182, yn= 4025

  I remembered the FIR filter implementation i did yesterday, if I set
xn=1000, then yn=1000.

 correct some mistakes:
                      if   xn=2048,  yn=969*2;
                          xn=4096,  yn=1968*2;
                          xn=8182, yn=4025*2;