On Thu, Apr 29, 2010 at 4:31 PM, Alexandros Diamantidis <adia@hellug.gr> wrote:

Hello all,

I got a new computer recently, with onboard audio (ATI Technologies
Inc SBx00 Azalia (Intel HDA) according to ALSA). I discovered that if
there's no microphone connected, jack (jackdmp 1.9.5) doesn't run and
outputs a continuous stream of "alsa_driver_xrun_recovery
JackAudioDriver::ProcessAsync: read error, skip cycle". As soon as I
connect a mic, it works normally.

When starting it with the -P option (playback only), mic presence
doesn't affect jack operation, but of course there are no capture ports
available.

It doesn't make much of a difference for me right now, but just for
curiosity's sake, I'm wondering if it's possible to start jack without a
mic and have capture ports appear automatically when one is connected.

you appear to have an HDA chipset with "jack detection" (it detects when a jack is inserted). you can't do what you asked about, but you can get close to it.
use a h/w mixer control application (e.g. the ugly and terminal-based but-so-far-unmatched alsamixer) to set the capture source of the device back to, perhaps, "line in". then later, switch it to the "mic". JACK pays (almost) no attention to the state/settings of the h/w mixer, so it has no clue what you're recording from or whether or not a mic is plugged in.

--p