Re: [Discuss-gnuradio] Problem with my modified IP tunnelling example

[Jeremy Chew]

Hi,

I'm using an older version as this is what that came when I downloaded GR a 
few months ago and I haven't seen a need to change what I have installed. 
I'm new to GR, Linux and Python so I'm more eager to debug what I have 
without introducing even newer stuff.

Anyway, the earlier problem was due to a C++ bug affecting another thread. 
This has been fixed. Now there's a problem with passing the packets created 
in the C++ extension, called sm, to Python.

The following describes what I do, which is setting the callback, and then 
calling the callback.

SETTING THE CALLBACK POINTER IN THE C++ EXTENSION

The Python call that is to receive the packet from the C++ extension is 
inherited from null_mac class and is named self.fg.send_pkt(). It is passed 
from a sub-class of null_mac in Python to the extension with:

sm.settx2llecallback(self.fg.send_pkt)

The corresponding C++ call is:

static PyObject*s_pcTxDnCallback=0;
...
static PyObject*sm_settx2llecallback(PyObject*a_pcSelf,PyObject*a_pcArgs)
{...
   PyObject*l_pcCallback=0;
...
   if(PyArg_ParseTuple(a_pcArgs,"O:set_callback",&l_pcCallback))
   {
       if(PyCallable_Check(l_pcCallback))
       {...
           Py_XINCREF(l_pcCallback);
           s_pcTxDnCallback=l_pcCallback;
...
}

When the above executes, PyCallable_Check() seems to run with no error.

PASSING PACKETS FROM THE EXTENSION TO PYTHON CODE

Later, a packet is created in the C++ extension in the form of an unsigned 
char array. To pass it to the Python IP tunneling code, I do the following:

BOOL Tx2PyLle(unsigned char*data,UINT16 len)
{
...
   PyObject*l_pcArgs=0;
...
   
l_pcArgs=Py_BuildValue("(s#)",reinterpret_cast<char*>(data),static_cast<INT32>(len));
   if(l_pcArgs )
   {...
      assert(s_pcTxDnCallback);
       ...;
       PyObject*l_pcRet=PyEval_CallObject(s_pcTxDnCallback,l_pcArgs);
...
}

This function above has a segmentation fault at PyEval_CallObject().

My queries are:

1) Is the callback to Python passed and set correctly in the extension?

2) Is it right to assume that in Python, the packets are Python strings?

Thanks a lot,
Jeremy

----- Original Message ----- 
From: "Eric Blossom" <address@hidden>
To: "Jeremy Chew" <address@hidden>
Cc: <address@hidden>
Sent: Tuesday, November 28, 2006 2:53 AM
Subject: Re: [Discuss-gnuradio] Problem with my modified IP tunnelling 
example


> On Mon, Nov 27, 2006 at 07:05:26PM +0800, Jeremy Chew wrote:
> > Hi,
> >
> > I've tried the IP tunnelling example in
> > gnuradio-examples-0.7/python/gmsk2/tunnel_ip_null_mac.py and it seems to
> > work fine.
> >
> > I've since been modifying the IP tunnelling example to use my MAC in 
> > place
> > of null_mac. I have fixed the code to use the new MAC in the form of a 
> > C++
> > extension.
> >
> > However, now when I try to run the modified IP tunnelling example, the
> > program craches at either of two different points in __init__() of
> > transmit_path class with the message 'Floating exception'. The exact 
> > crash
> > point seems to depend on which directory I run the example in.
> >
> > What's wrong? What is a floating exception?
> >
> > Thanks,
> > Jeremy
>
> Sorry, I've got no clue.
>
> Any particular reason you're using really old code?
> Consider using gnuradio-3.0.2 or svn.
>
> See http://gnuradio.org/trac/wiki
>
> Eric