Re: [Discuss-gnuradio] Problem w. block Message Source

[Tom Rondeau]

On Tue, Jan 28, 2014 at 12:34 PM, Jose Rodriguez
<address@hidden> wrote:
>
> On Tue, Jan 28, 2014 at 12:05 PM, Tom Rondeau <address@hidden> wrote:
>>
>> On Tue, Jan 28, 2014 at 11:10 AM, Jose Rodriguez
>> <address@hidden> wrote:
>> >
>> > Hi,
>> >
>> > I am a beginner at Gnuradio and I am working on writing some simple
>> > graphs.
>> > I am having a problem w. the block "Message Source".
>> >
>> > I got the block "Message Strobe" connected to "Message Source" (the goal
>> > is
>> > to extract the data bytes and feed them to a "Packet Encoder" block).
>> >
>> > The graph builds OK but when run I get:
>> >
>> > Using Volk machine: avx_64_mmx_orc
>> > Traceback (most recent call last):
>> >   File "/home/joser/Desktop/xx/top_block.py", line 120, in <module>
>> >     tb = top_block()
>> >   File "/home/joser/Desktop/xx/top_block.py", line 72, in __init__
>> >     self.blocks_message_source_0 =
>> > blocks.message_source(gr.sizeof_char*1,
>> > blocks_message_source_0_msgq_in)
>> > NameError: global name 'blocks_message_source_0_msgq_in' is not defined
>> >
>> >>>> Done
>> >
>> > Any idea what the problem could be?
>>
>> It's certainly not obvious from that error message, but what's going
>> on is that you are using the two different message systems in GNU
>> Radio. The message_source is designed to work with a special msg_queue
>> concept while the message strobe block is part of the newer
>> asynchronous message passing architecture. Notice how they are
>> different colors and so don't belong together.
>>
>
> OK, yes they are different colors (light grey vs. dark grey), my mistake.
> Quick question, what block can/should be used to extract the data in the
> message generated by Message Strobe?

Take a look at the PDU to tagged stream block. The message passing
page in the manual gives brief coverage of this block and PDUs in
general, but it's rather sparsely documented.

>> We should add some language to the message passing page in the manual
>> to better explain this distinction.
>>
>> > I checked: http://gnuradio.org/doc/doxygen/page_msg_passing.html and at
>> > the
>> > bottom is says to look at the examples in gr-blocks/examples/msg_passing
>> > but
>> > I get missing link errors when I load these files in my setup.
>> >
>> > My setup is gnuradio 3.7.2.1 running in Ubuntu 12.04.4 LTS.
>> >
>> > thanks for any help,
>> >
>> > Jose Rodriguez
>> > address@hidden
>>
>> What exactly do you mean by link errors? Are you talking about missing
>> blocks in the GRC graph or when you run it, you are getting linking
>> errors in the library? Neither of which should be happening on that
>> release.
>>
>> Tom
>
>
> By "missing link errors" I meant that when the grc file is loaded, some
> blocks are not connected. For example, when I load
> gr-blocks/examples/msg_passing/strobe.grc in the screen there are two
> Message Strobe blocks whose output are not connected. Also I get the
> following output:
>
> Loading:
> "/home/joser/gnuradio/gnuradio/gr-blocks/examples/msg_passing/strobe.grc"
>>>> Error: Connection between blocks_message_strobe_0(0) and
>>>> blocks_message_debug_0(0) could not be made.
>     source key "0" not in source block keys
>>>> Error: Connection between blocks_message_strobe_0_0(0) and
>>>> blocks_pdu_to_tagged_stream_0(0) could not be made.
>     source key "0" not in source block keys
>>>> Error: Connection between blocks_tagged_stream_to_pdu_0(0) and
>>>> blocks_message_debug_0(2) could not be made.
>     source key "0" not in source block keys
>>>> Done
>
> It could be my setup (I have reloaded Gnuradio several times, I have found
> that there are many example grc files out there which is great, but often
> they are based on 3.6. I tried to have both releases 3.6 and 3.7 installed
> with no success). Anyway, thanks for the quick response.
>
> Jose
> address@hidden

Erp, nope, that's our fault. I looked back to make sure that example
was updated with 3.7, but we introduced another bug due to the
handling of message connections GRC, which ended up breaking these
examples. This is fixed, but not in a release, yet (3.7.2.2 will be
out soon and include the fix for this).

In the meantime, it's not that difficult to read through that list of
errors and recreate the connections. Or download the example from our
maint branch:
http://gnuradio.org/cgit/cgit.cgi/gnuradio/tree/gr-blocks/examples/msg_passing/strobe.grc?h=maint

Hope that helps,

Tom