[Discuss-gnuradio] ofdm reception affected by python threading?

[Veljko Pejovic]

Hi,

I'm using two USRP2 with XCVR2450s, a week old gnuradio git master and
Ubuntu 9.10.

A few months ago while using the OFDM code I observed that I tend to
receive (or send?) packets in groups, although I was sending them
individually.

Now, I finally isolated the problem. I added a few simple print lines:

"Message inserted in HAVE_HEADER" - whenever a message is enqueued in
STATE_HAVE_SYNC of ofdm_frame_sink.cc

and

"Message picked up from the queue" - in queue_watcher_thread in
ofdm.py, every time the message is fetched from the queue.

The output that I expected was:

Message inserted in HAVE_HEADER
Message picked up from the queue
Message inserted in HAVE_HEADER
Message picked up from the queue
...

However, I'm getting rather inconsistent output (this is a sample,
check the attachment for the first few seconds of the output):

Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message picked up from the queue
Message picked up from the queue
Message picked up from the queue
Message picked up from the queue
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message inserted in HAVE_HEADER
Message picked up from the queue
Message picked up from the queue
Message picked up from the queue
Message picked up from the queue
Message picked up from the queue

So, it is definitely the receiver that has problems. It looks as if
"msg = self.rcvd_pktq.delete_head()" in queue_watcher_thread in
ofdm.py is not checked frequently enough. Could it be that Python does
not switch threads fast enough? Note, I do have real time scheduling
enabled.
Any ideas on how to get around this?


Thanks,


Veljko

output_rx.txt
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