UHD Error handling from GNU Radio/Python

Hi all,

I am interested in being able to recover from UHD Error conditions such
as not finding a USRP on startup or an Ethernet cable getting knocked
loose (USRP N200). I implemented an uhd_async_message source but all I
can do with that is read error codes corresponding to sequence errors,
late packets, underruns, etc. It’s nice to have the ability to take
action based on these messages, but if an Ethernet cable gets knocked
loose, nothing gets sent to the message queue (at least, not that I
could find). Instead, UHD prints to stdout using some other thread and
then my script hangs.

I hacked UHD’s error printing code to do an exit after it prints
whatever error occurred, and then a bash script handles restarting the
Python program that’s controlling GNU Radio behavior. I’m aware that
there is a way to register a message handler function with UHD so that
it won’t just print to the screen and hang. Is there any way to
implement this handler in Python and register the function with UHD? I
don’t normally post to both lists to avoid redundant spamming, but I’ll
take a leap of faith here. :slight_smile:

Thanks,
Sean Nowlan

P.S. - I’ll sneak this question in with the technical one above: is the
GNU Radio conference free to attend? Is there any registration required?
Didn’t see any such thing on the site, so I’m assuming it’s free and the
public can just show up and enjoy some awesomeness.

On 07/19/2012 09:42 PM, Nowlan, Sean wrote:

some other thread and then my script hangs.

I hacked UHD’s error printing code to do an exit after it prints
whatever error occurred, and then a bash script handles restarting
the Python program that’s controlling GNU Radio behavior. I’m aware
that there is a way to register a message handler function with UHD
so that it won’t just print to the screen and hang. Is there any way
to implement this handler in Python and register the function with
UHD? I don’t normally post to both lists to avoid redundant spamming,
but I’ll take a leap of faith here. :slight_smile:

I think I see your point. There really isnt a good way to know that some
internal thread died. Whether it be in UHD or a gnuradio worker thread.

It might be a decent idea to queue up an async message into the queue
when an internal thread dies. Not sure how you might get the info from a
gnuradio scheduler thread though.

In the short term, if you do try to communicate with the device object
in someway that involves an over-the-bus communication, and the
transport is down, you will get a nice exception thrown all the way into
python which you can catch and react to.

Example, periodically set_time_source(…) which is harmless to do, but
causes bus traffic.

-josh

least, not that I could find). Instead, UHD prints to stdout using

I think I see your point. There really isnt a good way to know that some internal
thread died. Whether it be in UHD or a gnuradio worker thread.

In this case, I’m not sure if a thread actually dies. It just goes into
a loop or some kind of blocking state waiting for UHD control message
responses.

It might be a decent idea to queue up an async message into the queue when an
internal thread dies. Not sure how you might get the info from a gnuradio
scheduler >thread though.

I haven’t needed this, but I could see how it could be useful.

In the short term, if you do try to communicate with the device object in someway
that involves an over-the-bus communication, and the transport is down, you will
get a nice exception thrown all the way into python which you can catch and react
to.

I’ve seen it throw an exception if the USRP is not connected when the
UHD GNU Radio block is first instantiated. I’ll try running a heartbeat
“while True” loop in the main thread and see if I can get it to throw an
error if I yank the Ethernet cable after the top block has already been
started.

I’m still curious though, do you know of a way to register a message
handler function with UHD from Python? If I add %include
<uhd/utils/msg.hpp> to gnuradio/gr-uhd-swig/uhd_swig.i, will SWIG know
how to translate a function pointer to Python, or would this require UHD
to implement a shared pointer interface?
http://files.ettus.com/uhd_docs/manual/html/general.html#disabling-or-redirecting-prints-to-stdout

Hi!

I am trying to do the same thing, did you have any success registering
message_handler with UHD?

best regards,
Urban K.

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