[mythtv-users] AMD guide to building a Media PC

Yan Seiner yan at seiner.com
Sat Mar 3 16:05:40 UTC 2007

Brian Wood napsal(a):
> On Mar 3, 2007, at 7:52 AM, Yan Seiner wrote:
>> Which video card do you have?
>> I have a Sempron 3000, which should be enough, and my TV runs at 720p,
>> so I guess I should be able to show HD.  But it fails miserably with
>> prebuffering pauses and the CPU is pegged > 98%, so something is  
>> wrong.
>> I have another system with an Athlon XP 2000+, which shows HD content
>> just fine at 800x600 on TV out with 65% CPU.
>> The big difference between the two machines is that the Sempron has an
>> nVidia 6200 whereas the Athlon has an nVidia 5200...  ISTR reading  
>> that
>> the 5200 is actually better at HD playback?  Can anyone confirm that?
> You say the "big difference" but I'll bet there are others. What  
> driver versions? What settings (vsync or not etc.)? What options in  
> your X configuration file? What buss is the card on and what  
> parameters (fast writes etc.)?
I've been matching the two as closely as possible, to try and get a 
handle on this.

Both use nVidia 9746 driver, both xorg files are as close as I can get 
them, and both machines are a current install of Debian Etch, with 
self-compiled myth-0.20-fixes.

One minor difference is that the source for the XP was built with 
--march=athlon-xp, whereas the sempron defaulted to pentiumpro.  I am 
rebuilding now with --march=athlon; we'll see if that makes any difference.

Not sure about vsync; what do I need to look for there?

> The biggest difference I'm aware of between the 5xxx and the 6xxx  
> cards is that the 5xxx ones use chroma key while the 6xxx uses  
> overlay, but I'm sure there are other differences. I think this shows  
> up more in things like the OSD and not so much in actual video  
> playback where you're not keying or overlaying as a rule.
> Then there's the difference between a Sempron and an Athlon, major  
> differences which might well show up in multimedia apps like HD  
> decoding. Even the cache difference might be significant. A Sempron  
> is a low-end CPU and I really wouldn't expect too much from it.
I suspect that may be the root cause; there were a variety of Semprons, 
and some of the lower numbered Semprons had much bigger caches than 
others.  Mine is one of the low-low-end, 128K cache ones...

> It's been said that a "modern" AMD processor of the "3000+" rating  
> should be able to do HD but I'm not sure I'd consider a Sempron as  
> "modern" these days, but I'd still look at your video driver and X  
> config settings.
I've been looking...  Been through the wiki, xorg.conf, etc.  The only 
difference I picked up on just now is that the Athlon had nvagp set to 3 
and the Sempron had it set to 1....

I'll see if that makes any difference.

I've also tweaked the nfs server settings per the wiki.  We'll see when 
I get a chance to reboot.  (It's saturday AM, and the kids are getting 
their fill of shlock-o-vision.  Before long they'll be out riding bikes 
and stuff and I'll do more testing....)

> Although AMD denies it, their model numbers really are, or at least  
> were, intended to indicate performance relative to a P4 of the same  
> vintage, since people were simply comparing clock speeds and Intel  
> was obviously coming out ahead.
The whole Athlon numbering scheme is an exercise in marketing 


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