[Discuss-gnuradio] "check topology failed on audio_alsa_sink"

Hi everyone,

I'm having problems making the audio output work because of a "RuntimeError: check topology failed on audio_alsa_sink(7) using ninputs=1, noutputs=0". I did spend a few hours searching the archives and the web, but no luck.

Hardware: RPi model 3, the signal comes from an RTL-SDR dongle (the error was reproducible with the gnu-radio and gr-osmosdr from the jessie distribution. I installed the latest just in case it made a difference).

Software: gnuradio 3.7.9 installed from jessie-backports, gr-osmosdr v0.1.4-72-g164a09fc (0.1.5git) built from sources, rtl-sdr built from sources. 

The flow is very simple, I want to get the audio going before doing the real work (for testing purposes, I tuned to an NBFM weather station). I'm still a beginner so maybe something is not correct, though. See further down for a note on the Audio Sink.

I would appreciate some guidance as I don't understand the nature of the problem. Some were saying that something might be wrong with the audio sample rate, but it's not clear to me if that's the case. I also checked in the Audio Properties (right-clicking on the speaker icon top-right) that it's the Analog not HDMI output that's selected. Also, there is no other program using the sound card.

Many thanks in advance,

JL

Here's the output when I execute the program:

Generating: '/home/pi/top_block.py'

Executing: '/usr/bin/python -u /home/pi/top_block.py'

Using Volk machine: neon_hardfp_orc

gr-osmosdr v0.1.4-72-g164a09fc (0.1.5git) gnuradio 3.7.9

built-in source types: file fcd rtl rtl_tcp rfspace airspy redpitaya 

Using device #0 Realtek RTL2838UHIDIR SN: 00000001

Found Rafael Micro R820T tuner

gr::log :INFO: audio source - Audio sink arch: alsa

len(audio_taps) = 2313

gr::log :ERROR: audio_alsa_sink0 - [plughw:0,0]: set_channels failed: Invalid argument

Traceback (most recent call last):

  File "/home/pi/top_block.py", line 185, in <module>

    main()

  File "/home/pi/top_block.py", line 174, in main

    tb.start()

  File "/usr/lib/python2.7/dist-packages/gnuradio/gr/top_block.py", line 109, in start

    top_block_start_unlocked(self._impl, max_noutput_items)

  File "/usr/lib/python2.7/dist-packages/gnuradio/gr/runtime_swig.py", line 4876, in top_block_start_unlocked

    return _runtime_swig.top_block_start_unlocked(*args, **kwargs)

RuntimeError: check topology failed on audio_alsa_sink(7) using ninputs=1, noutputs=0

>>> Done (return code 1)

Based on some of the results when searching for the error, I tried both leaving the audio device empty or putting plughw0,0 (as suggsted by the block's documentation). I also tried hw:0,0 without any success either.

Below are the audio devices:

pi@x:~/gr-osmosdr/build $ cat /proc/asound/cards

 0 [ALSA           ]: bcm2835 - bcm2835 ALSA

                      bcm2835 ALSA

pi@x:~/gr-osmosdr/build $ aplay -L

null

    Discard all samples (playback) or generate zero samples (capture)

sysdefault:CARD=ALSA

    bcm2835 ALSA, bcm2835 ALSA

    Default Audio Device

dmix:CARD=ALSA,DEV=0

    bcm2835 ALSA, bcm2835 ALSA

    Direct sample mixing device

dmix:CARD=ALSA,DEV=1

    bcm2835 ALSA, bcm2835 IEC958/HDMI

    Direct sample mixing device

dsnoop:CARD=ALSA,DEV=0

    bcm2835 ALSA, bcm2835 ALSA

    Direct sample snooping device

dsnoop:CARD=ALSA,DEV=1

    bcm2835 ALSA, bcm2835 IEC958/HDMI

    Direct sample snooping device

hw:CARD=ALSA,DEV=0

    bcm2835 ALSA, bcm2835 ALSA

    Direct hardware device without any conversions

hw:CARD=ALSA,DEV=1

    bcm2835 ALSA, bcm2835 IEC958/HDMI

    Direct hardware device without any conversions

plughw:CARD=ALSA,DEV=0

    bcm2835 ALSA, bcm2835 ALSA

    Hardware device with all software conversions

plughw:CARD=ALSA,DEV=1

    bcm2835 ALSA, bcm2835 IEC958/HDMI

    Hardware device with all software conversions