JACK audio connection kit jackd daemon fails to start on RaspberryPi

Question

I am running Raspberry Pi image 2012-07-15-wheezy-raspbian.zip and I have a CMedia 108 USB audio adapter installed RPi.

Trying to start jackd using built in audio

jackd -r -d alsa -d hw:0

fails to start

JACK compiled with System V SHM support.
loading driver ..
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|32bit
control device hw:0
ALSA: Cannot open PCM device alsa_pcm for capture. Falling back to playback-only mode
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2 periods
ALSA: mmap-based access is not possible for the playback stream of this audio interface
ALSA: cannot configure playback channel
cannot load driver module alsa 

Using usb audio

jackd -r -d alsa -d hw:1  

immediately exits, instead of running in background.

JACK compiled with System V SHM support. 
loading driver .. 
creating alsa driver ... hw:1|hw:1|1024|2|48000|0|0|nomon|swmeter|-|32bit 
control device hw:1 
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2 periods 
ALSA: final selected sample format for capture: 16bit little-endian 
ALSA: use 2 periods for capture 
ALSA: final selected sample format for playback: 16bit little-endian 
ALSA: use 2 periods for playback  

Any ideas?

Answer 1

The onboard sound card doesn't work directly with JACK, but a USB sound card like the C-Media should work. You will need a patched version of JACK though: http://wiki.linuxaudio.org/wiki/raspberrypi The JACK packages in the official Raspbian repositories do not work because they use packed structs which will yield a bus error when starting JACK.

After having installed JACK from the repository try starting JACK like this:

jackd -P84 -p32 -t2000 -d alsa -dhw:Device -p 128 -n 3 -r 48000 -s

This will run JACK with a system latency below 10ms. For me this works well with my $2 C-Media sound card.