[op25-dev] difference between op25.decoder_bf and op25.decoder_ff

Sean Watkins sean.watkins at gmail.com
Fri Mar 23 04:49:51 UTC 2012


DVD-T? Really? What kind of receiver just a usb ATSC tuner etc? Scary to
what to think I could do with DVB-S2 and Gnuradio lol
Ok great 

Back to the decoder – ff that fills in some blanks.

I put a slicer ahead of the decoder - now I get segv inside the decoder -
inside  the general_work method:

(running python under gdb...)

[New Thread 0x7fffdc1bd700 (LWP 9511)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffdc9be700 (LWP 9510)]
op25_decoder_bf::general_work (this=0x27666b0,
nof_output_items=46,nof_input_items=..., input_items=<value optimized out>,
output_items=...)
    at op25_decoder_bf.cc:92
92            float *out = reinterpret_cast<float*>(output_items[0]);
(gdb) bt
#0  op25_decoder_bf::general_work (this=0x27666b0, nof_output_items=46,
    nof_input_items=..., input_items=<value optimized out>,
output_items=...)
    at op25_decoder_bf.cc:92
#1  0x00007ffff5f01a3e in gr_block_executor::run_one_iteration() ()
   from /usr/local/lib/libgnuradio-core-3.5.3git.so.0.0.0
#2  0x00007ffff5f232cf in
gr_tpb_thread_body::gr_tpb_thread_body(boost::shared_ptr<gr_block>, int) ()
from /usr/local/lib/libgnuradio-core-3.5.3git.so.0.0.0
#3  0x00007ffff5f1c71f in
boost::detail::function::void_function_obj_invoker0<gruel::thread_body_wrapp
er<tpb_container>, void>::invoke(boost::detail::function::function_buffer&)
() from /usr/local/lib/libgnuradio-core-3.5.3git.so.0.0.0
#4  0x00007ffff5c4d015 in boost::detail::thread_data<boost::function0<void>
>::run() () from /usr/local/lib/libgruel-3.5.3git.so.0.0.0
#5  0x00007ffff5193b70 in thread_proxy ()
   from /usr/lib/libboost_thread.so.1.40.0
#6  0x00007ffff7bc69ca in start_thread () from /lib/libpthread.so.0
#7  0x00007ffff6aa0cdd in clone () from /lib/libc.so.6
#8  0x0000000000000000 in ?? ()
(gdb)

The code in question looks like:

int
op25_decoder_bf::general_work(int nof_output_items, gr_vector_int&
nof_input_ite
ms, gr_vector_const_void_star& input_items, gr_vector_void_star&
output_items)
{
...

    float *out = reinterpret_cast<float*>(output_items[0]);

I'm not totally familiar with blocks in GNURadio -  seems like output_items
isn't initialized... 



Sean



From: op25-dev at yahoogroups.com [mailto:op25-dev at yahoogroups.com] On Behalf
Of Steve Glass
Sent: Thursday, March 22, 2012 6:49 PM
To: op25-dev at yahoogroups.com
Subject: Re: [op25-dev] difference between op25.decoder_bf and
op25.decoder_ff

  
Hi,

I've just got a funcube myself and just this morning support for it made it
into the GNURadio trunk. That should make using them lots easier. I am
looking forward to seeing the DVB-T support get done because that will make
using SDR much cheaper (23USD delivered!).

The question you ask concerns the interface to the decoder... the _ff
version has float inputs and outputs and the other takes bytes (actually
two-bit symbols) inputs and float outputs. The latter needs a slicer before
it but that is conceptually the right thing to do and so the _ff version is
deprecated. Hope that helps.

Stevie


On 23 March 2012 07:48, bdapriv01 <bdapriv01 at gmail.com> wrote:
  
Hi

Whats the difference between these 2? 

I'm new to Gnuradio & python to be honest; I'm writing my own ap25 listener
for the funcube...

So far, I've got my software tuning, FM decoding, and then sending data into
the FSK4 decoder; I can see it fine tuning.. but I don't get anything out of
the decoder_bf function.

Is there any easy way, to debug what its doing?? 

Digging around in code there doesn't seem to be much debugging.

I did create some network sinks, and forward the output of the FM demod to a
a scope inside gnuradio companion.. the signal looks like FSK4 with the
funky phase changes.

Sean 



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