[mythtv-users] problems on playback due to no ACPI and IRQ sharing?

[Adam Gianola]

I also had a similar problem, which it seems has been cured.  I'm not
sure of the cause or solution, but I'll describe what I observed and
what changed as maybe it might help you.

Currently my mythtv setup is on a FC3 box following Jarod's excellent
howto.  The machine has a Soyo SY-P4RC350 mainboard with a P4 2.4GHz
with 512MB PC2700.  I've disabled the onboard ATI video, and am using
an agp nvidia 5200 video card instead.  The display is on the vga
output of this card, and I'm using the onboard sound.  I am using a
PVR-250 for video capture, and have a pchdtv hd3000 card installed
which is not in use currently, since I can't figure out how to make it
and the 250 play nicely (OTA HD reception is poor in my area to boot).
 I also have a 1394a card which I intend on using with the new
functionality of myth 0.17 when I upgrade to digital cable.

When playing back divx or xvid avi's (with mplayer from within myth)
across the network from a windows smb share I observed something
similar to what you described, the video skipping a few second every
couple of minutes.  I never tried playing avi's from the myth box
itself, however.  I could rewind and the video would play fine where
it skipped before, but again every few minutes it would skip a second
or two.  I turned up the mplayer cache to 5000 kB (-cache 5000
option), which maybe helped some network streaming issues, I don't
think it solved the skipping problem.  Certainly I observed some irq
problems as occassionally I would see a nice little popup which says
"Disabling IRQ 15" (or some such number, which corresponds to the
PVR-250).  After this video capture doesn't work, naturally, until
rebooted.  I added the option "acpi=off" to my grub.conf at some
point.  I don't think that fixed either of the problems.  Some time
later I upgraded from the 2.6.9-1.681_FC3 kernel to 2.6.10-1.766_FC3,
after which I had sound card issues (volume muted or some such
nonsense).  Reviewing the dmesg carefully upon boot after this kernel
upgrade, I discovered some trouble about irq sharing (sharing disabled
I believe) which the dmesg suggested the option "pci=usepirqmask".  I
tried it and never looked back.  I don't think i have seen the
'disabling irq 15' or video skipping problem since, but maybe i'm
wrong.  I never bothered to look at the cpu usage, since it should
have plenty of power to play back whatever i was throwing at it. 
hell, i have an xbox frontend in the bedroom that works flawlessly for
the same playback across the network.  I also had some troubles with
the playback of videos recorded from the pvr-250 which i finally
solved by looking carefully at jarods guide and adding "alias msp3400
msp3400-ivtv" to the modprobe.conf.  At some point I also added the
"-ao alsa"  to the video playback command for mplayer to make sure it
was using alsa like it should be.

I don't know which of these solved the issues (or if it is even
solved), but I don't recall seeing this stupid skipping problem for a
few weeks now.  It certainly is irritating, i know.  I'm hoping it is
solved permanently.  it couldn't hurt to try the kernel options i
mentioned above.  maybe it will fix your problems.

Good luck,
Adam