//the modem len is 160

buffer tmp_for_readi[160 * 3 == 480];
buffer tmp_for_writei[160 * 3 == 480];

update_ptr(ptr,num){
	if (ptr + num) > 480
	   ptr += ( ptr+num ) - 480;
	else
	   ptr += num;

}


check_tmp_for_writei_pos(){
	if (readptr + 160 > writeptr);
	   //push writeptr ahread because of collision
	if (writeptr + 160 > readptr);
	   //push readptr  ahread because of collision
	else if (readptr > writeptr+160)
	   handle_xruns();
}


readi_callback(){
	check_tmp_for_readi_pos();
	if ( (readptr - writeptr) < N )
    	   //buffer overrun
       	   fill_with_silence();
	   return;
	else
	   N = readi(audiobuf);
	   Memory.copy(audiobuf,tmp_for_readi)
	   update_ptr(writeptr,N);
	   return;
}

writei_callback(){
	check_tmp_for_writei_pos();
	if ( (writeptr-readptr) < N )
	   //buffer underrun
	   fill_with_silence();
	   return;
	else
	   N = writei(tmp_for_writei,card);
	   update_prt(readptr, N);
	   return;
}


write_to_modem(){
	Memory.copy(modem_write,tmp_for_readi,160);
	update_ptr(readptr,160);
}

read_from_modem(){
	Memory.copy(tmp_for_writei,modem_read,160);
	update_prt(writeptr,160);
}