[mythtv-users] Firewire on a combo backend/frontend

Allan Wilson allanwilson at gmail.com
Mon Jul 31 18:27:13 UTC 2006


On 7/31/06, John P Poet <jppoet at gmail.com> wrote:
>
> Since capturing firewire video data on my backend machine resulted in
> a constant stream of discontinuity errors, I turned my frontend
> machine into a combo backend/frontend, and hooked the firewire up
> there.
>
> On this frontend machine, I am able to capture pretty clean video via
> firewire.  However, if I try to watch anything while it is recording
> via firewire, the video is very jumpy, and I get a lot of "video is 30
> frames behind audio" type messages.  This is on a Athlon X2 4200,
> runing 2.6.17.7.
>
> I figured that it had been long enough since Jim Westfall submitted
> his ieee1394 dma patch that it would be a part of 2.6.17, but I
> discovered it was not.  After applying his patch:
>
> http://www.gossamer-threads.com/lists/mythtv/dev/187783#187783
>
> and building a new kernel, the video playback while recording problem
> is now solved.  I did have to "hand" apply the patch because the
> formatting of the dma.c file in 2.6.17 has changed slightly.  Applying
> this patch caused the CPU usage of mythbackend to drop from 10-11% to
> 3-4% while recording via firewire.
>
> Unfortunately, I now had an audio problem.  The sound would drop-out
> for a fraction of a second, every couple of seconds.  This only
> happened if I was recording via firewire at the same time.  I figured
> my firewire port and my sound card must be sharing an interrupt, but a
> quick look at the motherboard manual disproved that theory.  I then
> check the latencies of those two devices (lspci) and discovered that
> both were at 32.  After adjusting both up to 64 (setpci), my audio
> problem is also solved.
>
> I still have a little problem with channel changes.  The channel
> change program I am using works 100% of the time, when I am testing it
> via the command line.  With Myth in control it only seems to be 75%
> reliable.  This program changes channels on my SA3250HD via firewire.
>
> I figured that to get 100% reliable channel changes, I would switch to
> lirc.  I have an ir-blaster and decided to hook it up along side my
> ir-reciever.  Unfortunately, both are serial and therefore use the
> lirc_serial driver.  It turns out the lirc_serial driver cannot handle
> two serial ports at the same time.  Furthermore, you cannot run two
> lirc_serial drivers at the same time.  To get around this, some people
> have hacked the lirc source tree to create a lirc_serial1.  This is
> actually much harder than it sounds, and is generally a royal PITA.  I
> may try a little harder to get channel changes to work via firewire...
>
>
> John
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>

Wow, great post. I am going to look in to the patch that you mentioned and
try your fix for the audio problem b/c I am having the same thing. Let me
know if you want a copy of my sa3250ch  file because I don't have any
problems. Thanks for taking the time to post.

Allan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mythtv.org/pipermail/mythtv-users/attachments/20060731/a3c779cf/attachment.htm 


More information about the mythtv-users mailing list