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Re: [Discuss-gnuradio] RTTY receiver

From: CEL
Subject: Re: [Discuss-gnuradio] RTTY receiver
Date: Wed, 12 Jun 2019 16:40:39 +0000

Hi Barry,

On Wed, 2019-06-12 at 06:59 -0400, address@hidden wrote:
> Hi Kyeong,
> 1) In lib/radioteletype/baudot_encode_bb.h I tried replacing "static 
> const char" with "static const signed char", but it caused complications 
> in radioteletype/baudot_encode_bb.cc, so I took an alternate approach:

Wait, these filenames don't align with the ones I'm looking at – could
you verify we're both looking at the code from github.com/bitglue/gr-
radioteletype ?

Since this really just "spells out" the original code's intent, there
shouldn't be *any* problems at all with that. Maybe we should have a
look at these problems that arose?

> /*
>   * modified by Barry Duggan KV4FV
>   * 11 June 2019
>   * with RaspberryPi compiler, an error is produced comparing char and 
> signed char values.
>   * to circumvent this problem, I have changed all "-1" entries to "0x7f" 

Hm, -1 would be 0xFF in my math, wouldn't it? 0x7F is plain 127!

> in the table
>   * and in the code
>   */

By the way, spot the experienced old-school programmer: That's a
classical beautiful changelog comment from the pre-git era. Kudos :)
Always a pleasure to see. 

> So now the 'make' works without errors.

I presume that also includes the negative number comparisons in
lib/baudot_encode_bb_impl.cc 's general_work() function?

> 2) In 'sudo make install' I got the following:
> -- Installing: 
> /usr/local/lib/python2.7/dist-packages/radioteletype/_radioteletype_swig.so
> -- Set runtime path of 
> "/usr/local/lib/python2.7/dist-packages/radioteletype/_radioteletype_swig.so" 
> to ""
> which leads to a run-time error...
> Traceback (most recent call last):
>    File "/home/pi/gr-radioteletype/examples/rtty_demod.py", line 30, in 
> <module>
>      from radioteletype.demodulators import rtty_demod_cb
>    File 
> "/usr/local/lib/python2.7/dist-packages/radioteletype/demodulators.py", 
> line 9, in <module>
>      from radioteletype_swig import (
>    File 
> "/usr/local/lib/python2.7/dist-packages/radioteletype/radioteletype_swig.py", 
> line 21, in <module>
>      _radioteletype_swig = swig_import_helper()
>    File 
> "/usr/local/lib/python2.7/dist-packages/radioteletype/radioteletype_swig.py", 
> line 20, in swig_import_helper
>      return importlib.import_module('_radioteletype_swig')
>    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in 
> import_module
>      __import__(name)
> ImportError: No module named _radioteletype_swig
> So, where should '_radioteletype_swig.so' go, and how do I specify it?

That file should have gotten installed just OK if it was successfully
built. Are we sure that the build itself is successful? Sometimes, SWIG
(which generates our C++/Python glue half-automatedly) gets stuck, so
you really have to "make clean; make; make install". It's a bummer, but
I've seen it get nearly extinct over the years.

> 3) When I loaded 'examples/rtty_demod.grc', there was a missing block 
> 'pulseaudio_pa_sink'. 

That seems to be a block from a different out-of-tree module. 

However, you really don't need a pulseaudio block to speak to that most
common Linux user audio subsystem. Just replace that block with the
"audio sink" that GNU Radio brings itself.

> Where is it, and what does it do? 

Its purpose is probably to send audio to your Sound card, in the end.

> Since it didn't 
> seem directly required for the rest of the example to work, I deleted it 
> and the two blocks feeding it.
> 4) I really appreciate all that you and the others are doing to help 
> with this.

We really appreciate you asking here, so keep up the good work!


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