[mythtv-users] Changing two BIOS settings eliminated Jitter

Richard S anewbeginning2004 at hotmail.com
Mon Jan 19 02:17:52 EST 2004


I have given some of my set up and performance information below for 
reference. What I found may be unique to my system but felt I would pass on 
what I found. In searching for answers to why I have video jitter (sound was 
perfect) there was very little information here so I figured the problem 
must be my set up not the software. I have no idea really why changing these 
two parameters in the BIOS fixed my jitter problem but the difference is 
very significant. I have done a few recordings both ways and it is 
definitely a fix for at least my system. Not sure if both or only one of the 
folowing solved the problem I will have to do some more testing.

Works great if I set:

P2C/C2P Concurrency to disable (PCI to CPU, CPU to PCI concurrency)
AGP Fast Write to Disable (allows use of Fast Write Protocol for 4X AGP)

No idea why this works but it does appear to.

My system:

Epox8kta (KT133 chipset)
Duron 1.2ghz
Nvidia geforce2 GTS 32 meg (used with NVTV for output to TV)
PVR-250 (not sure what rev)
I have tested my system under full CPU load and video load and is stable and
temps are quite good all less than 50'C.
PSU Antec True power 380 watt
Creative labs live Value

Software:
OS is gentoo and I am using X (startx& to start environment)
Using mythtv CVS from 1/7/2004
Using IVTV 0.1.9 from 1/13/2004 (what a great advance)

Few performance numbers:
Using "top" command

CPU while recording only 2%
CPU while recording and watching 34%
CPU watching a recording only 33%

memory usage looks normal best I can tell and swap is working fine

Using hdparm -t /dev/hda

DMA is enabled
run while recording 31 mb/sec
run while recording and watching 31 mb/sec
run system idle 42 mb/sec
run watching a recording 31 mb/sec

Settings:

Jitter enabled (always bad if not enabled)
A/V sync enabled (always bad if not enabled)
Audio buffer (seems to be the same set or not)

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