Custom GRC block not accepting derived class objects

GNU Radio
1

I’m hoping for suggestions from the GRC and swig savvy folks on the
list.

I am trying to add LDPC functionality to gr-fec [1]. I made a GRC block
for a decoder class. The decoder class constructor accepts a base class
called fec_mtrx. In GRC, I am trying to give the decoder block an input
of an object of a class derived from fec_mtrx, called ldpc_R_U_mtrx. The
issue is that swig is giving an error that it expects the base class as
the argument.

From the swig documentation, this type of inheritance and type checking
seems to be fully supported and handled by swig. Is there something else
I need to consider in either the block’s cheetah template for the make
call, or the swig files?

The organization of the classes is like:

class FEC_API ldpc_R_U_mtrx : public fec_mtrx { };

class FEC_API ldpc_bit_flip_decoder_impl : public ldpc_bit_flip_decoder
{
public:
ldpc_bit_flip_decoder_impl(fec_mtrx *mtrx_obj, unsigned int
max_iter=100);
}

And then in variable_ldpc_bit_flip_decoder.xml I’ve got: self.$(id) =
$(id) = fec.ldpc_bit_flip_decoder.make($matrix_object, $max_iterations)

In my flowgraph, I provide the decoder block an input of a ldpc_R_U_mtrx
variable, and swig throws:
TypeError: in method ‘ldpc_bit_flip_decoder_make’, argument 1 of type
'gr::fec::code::fec_mtrx *

So to me, it seems like swig is not recognizing that the ldpc_R_U_mtrx
class derives from fec_mtrx. Not sure what to do about that except to
try and “un-inherit" the classes and overload the decoder constructor…

Thanks for any tips,
tracie

[1] github.com/tracierenea/gnuradio/tree/ldpc_mods

2

On Mon, Feb 23, 2015 at 4:06 AM, Perez, Tracie R
[email protected]
wrote:

seems to be fully supported and handled by swig. Is there something else I
ldpc_bit_flip_decoder_impl(fec_mtrx *mtrx_obj, unsigned int

So to me, it seems like swig is not recognizing that the ldpc_R_U_mtrx
class derives from fec_mtrx. Not sure what to do about that except to try
and “un-inherit" the classes and overload the decoder constructor…

Thanks for any tips,
tracie

[1] github.com/tracierenea/gnuradio/tree/ldpc_mods

Hey Tracie,

Unfortunately, I don’t have a good, easy answer for you. It does seem
like
this should work fine. I’m trying to think of examples where we’ve done
this before. The closest that I know of is with the constellation
objects
and something like the constellation_receiver that takes in just the
base
class. All of the function calls required are implemented in that base
class, but overloaded by the child class. It also has a function
“.base()”
that returns the pointer to the child object as the base class so we can
pass it through.

Figuring out how to get swig to work with the child class would probably
be
the better solution, but maybe you can use the constellation class model
to
get things going.

Tom

3

On Feb 23, 2015, at 9:30 AM, Tom R.
<[email protected]mailto:[email protected]> wrote:

On Mon, Feb 23, 2015 at 4:06 AM, Perez, Tracie R
<[email protected]mailto:[email protected]> wrote:
I’m hoping for suggestions from the GRC and swig savvy folks on the
list.

I am trying to add LDPC functionality to gr-fec [1]. I made a GRC block
for a decoder class. The decoder class constructor accepts a base class
called fec_mtrx. In GRC, I am trying to give the decoder block an input
of an object of a class derived from fec_mtrx, called ldpc_R_U_mtrx. The
issue is that swig is giving an error that it expects the base class as
the argument.

From the swig documentation, this type of inheritance and type checking
seems to be fully supported and handled by swig. Is there something else
I need to consider in either the block’s cheetah template for the make
call, or the swig files?

The organization of the classes is like:

class FEC_API ldpc_R_U_mtrx : public fec_mtrx { };

class FEC_API ldpc_bit_flip_decoder_impl : public ldpc_bit_flip_decoder
{
public:
ldpc_bit_flip_decoder_impl(fec_mtrx *mtrx_obj, unsigned int
max_iter=100);
}

And then in variable_ldpc_bit_flip_decoder.xml I’ve got: self.$(id) =
$(id) = fec.ldpc_bit_flip_decoder.make($matrix_object, $max_iterations)

In my flowgraph, I provide the decoder block an input of a ldpc_R_U_mtrx
variable, and swig throws:
TypeError: in method ‘ldpc_bit_flip_decoder_make’, argument 1 of type
'gr::fec::code::fec_mtrx *

So to me, it seems like swig is not recognizing that the ldpc_R_U_mtrx
class derives from fec_mtrx. Not sure what to do about that except to
try and “un-inherit" the classes and overload the decoder constructor…

Thanks for any tips,
tracie

[1]
github.com/tracierenea/gnuradio/tree/ldpc_modshttp://github.com/tracierenea/gnuradio/tree/ldpc_mods

Hey Tracie,

Unfortunately, I don’t have a good, easy answer for you. It does seem
like this should work fine. I’m trying to think of examples where we’ve
done this before. The closest that I know of is with the constellation
objects and something like the constellation_receiver that takes in just
the base class. All of the function calls required are implemented in
that base class, but overloaded by the child class. It also has a
function “.base()” that returns the pointer to the child object as the
base class so we can pass it through.

Figuring out how to get swig to work with the child class would probably
be the better solution, but maybe you can use the constellation class
model to get things going.

Tom

Thanks very much Tom for the feedback. I spent many more hours trying to
get swig to work directly with the child class and could never figure
out how, or find any clues about this issue in the swig documentation.
So as a workaround, I’ve added a get_base_ptr() function to the child
classes as you described that the constellation objects do.

I updated the xml file for the decoder to call the make function as:
self.$(id) = $(id) =
fec.ldpc_bit_flip_decoder.make(${matrix_object}.get_base_ptr(),
$max_iterations)

Now everything is swig’ing and working great.

Thanks again,
tracie