Re: [Discuss-gnuradio] loopback dropping final bits

[Eric Blossom]

On Thu, Mar 29, 2007 at 05:16:45PM -0700, Dan Halperin wrote:
> Greg Troxel wrote:
> > I wonder if there is data somewhere in the flowgraph that's less than
> > the amount needed for the next block to run.   Perhaps there should
> > be some sort of drain operation, or query for this (that adds over
> > components), so one can find out what's going on.
> >   
> 
> This appears to be the problem. For this configuration, the
> gr_clock_recovery_mm_ff block requires at least 10 inputs - the
> instrumented forecast method prints:
> 
> 16382 inputs required for 8191 outputs
> 8194 inputs required for 4095 outputs
> 4100 inputs required for 2047 outputs
> 2053 inputs required for 1023 outputs
> 1030 inputs required for 511 outputs
> 518 inputs required for 255 outputs
> 262 inputs required for 127 outputs
> 134 inputs required for 63 outputs
> 70 inputs required for 31 outputs
> 38 inputs required for 15 outputs
> 22 inputs required for 7 outputs
> 14 inputs required for 3 outputs
> 10 inputs required for 1 outputs
> 
> Since this block initially starts with 0 inputs and is not filled with
> other data following the run of the program, the last <10 samples are
> left in the flow graph. This could well be the problem with the last
> bits of the last packet always being dropped/corrupted, because if you
> were using queues and enqueued a message followed by a close_queue
> packet, they could well get shipped through the pipeline together.
> 
> This is where my expertise runs out; what's the right fix? Is it
> block-specific (either pre-pend 0s or detect the end of data and append
> 0s), or more general?
> 
> -Dan

Try applying this patch.  It has the effect of preloading ntaps()-1
zero's into the block's input stream.

Eric


--- gr_clock_recovery_mm_ff.cc  2006-12-20 10:40:57.000000000 -0800
+++ /tmp/gr_clock_recovery_mm_ff.cc     2007-03-29 17:59:42.000000000 -0700
@@ -61,6 +61,8 @@
   set_omega(omega);                    // also sets min and max omega
   set_relative_rate (1.0 / omega);
 
+  set_history(d_interp->ntaps());
+
   if (DEBUG_CR_MM_FF)
     d_logfile = fopen("cr_mm_ff.dat", "wb");
 }