Hello,
I am implementing transceiver based on acoustic waves. Now I have started
with receiver. Input to the receiver is from audio_alsa_source. I have written
a block named packet_detect based on sync_decimator to accept samples from
alsa_source.
Within the packet_detect block , I have been able to detect start of the frame.
Next how can I buffer the data beyond frame start point (ignoring all the
earlier samples) and pass it to the next higher blocks for processing.
I have pasted packet_detect code below, Please help me.
Thanks in advance
Raman
short pkd_detected=0;
packetdetection::packetdetection(size_t item_size, size_t nitems_per_block)
: gr_sync_decimator ("packetdetection",
gr_make_io_signature(1,1, item_size),
gr_make_io_signature(1,1,item_size * nitems_per_block),
nitems_per_block )
{
d_offset=0;
d_sigma1=0;
d_sigma2=0;
}
/* ----------- transformation process : Phi -------------- */
int
packetdetection::work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
size_t block_size = output_signature()->sizeof_stream_item (0);
const float *inbuf = ( const float*) input_items[0];
float *outbuf = (float*) output_items[0];
unsigned int i,j,k,itemsize;
float alpha1=0.125,alpha2=0.875,temp;
itemsize=block_size/sizeof(float);
if(!pkd_detected){
d_sigma1=*inbuf;
for(i=1;i<noutput_items * itemsize;i++) {//for i=2:M
temp=inbuf[i];
d_sigma2=alpha1*temp*temp + alpha2*d_sigma1 ;
//sigma(i)=alpha*Y(i)*Y(i)+(1-alpha)*sigma(i-1);
d_sigma1=d_sigma2;
if( d_sigma2>0.08){
pkd_detected=1;
printf("packet detected at %d \n",i);
for(k=0;k<(noutput_items *itemsize-i);k++){
outbuf[k] = inbuf[i];
}
d_offset+=k;
d_sigma1=0,d_sigma2=0;
return noutput_items;
}
}
return noutput_items;
}
else{
for(j=d_offset,i=0;j<(noutput_items * itemsize-d_offset);j++,i++){
outbuf[j] = inbuf[i];
}
d_offset+=i;
return noutput_items;
}
}
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