[mythtv-users] XvMC WriteAudio: buffer underrun -- partial solution

Justin The Cynical cynical at penguinness.org
Sat Sep 30 19:41:21 UTC 2006

Chris Skalenda wrote:

>> While I'm not sure if I had these problems in 0.19, I've been able to
>> get almost perfect XvMC playback by changing the NVAGP setting to "2"
>> in my xorg.conf:


> Setting NVAGP to 2 in my xorg.conf cleared up the prebuffering pause
> issues my mythtv system (Athlon XP 3000+, GeForce 6200, etc. Quite
> capable of playing HD) was having with 1080i playback with 0.20. 
> CPU usage dropped from 90-100% (with or without Bob on) to 30-40%. It
> doesn't even stutter when the OSD comes up.

Interesting.  Per the nvidia readme:

Option "NvAgp" "2"  ... use AGPGART, if possible

Please note that NVIDIA's internal AGP support cannot work if AGPGART is 
either statically compiled into your kernel or is built as a module and 
loaded into your kernel. Please see Appendix F for details. Default: 3.

So, it sounds almost like the system was not loading the AGP stuff..

Looking at lsmod on my system, I'm seeing that agpgart and sis_agp is 
loaded.  Xorg.conf currently has NVAGP commented out, so it should be 
loading the linux AGPGART.

According to /proc/driver/nvidia/agp/status:

cat /proc/driver/nvidia/agp/status
Status:          Enabled
Driver:          AGPGART
AGP Rate:        4x
Fast Writes:     Disabled
SBA:             Enabled

My video card is a MSI 6200 AGP fanless.  Those of you who have this 
card, what does the AGP status show for your card?

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