Retelling Yet Another Myth

Last month I put together my second MythTV box. I've become tired of my VIA Chrome box... video acceleration was a joke. So I thought that an onboard GeForce 7050PV would work since it had XvMC support. Plus NVIDIA's (binary-only) drivers were usually pretty good. Right?



I ordered Shuttle's SN68PTG5 AM2 case, figuring I could re-use an old AMD64 CPU I had and stuff the hard drive in from the previous MythTV box. When I got the case in it was a bit larger... and louder... than I expected. I needed to push my TV forward to get the box to fit behind it. The sheer amount of real estate I was able to work with made the opportunity worthwhile however - there was plenty of space around the motherboard, even with the ginormous heatsink installed.

Maneuvering around the box wasn't bad - I was able to put in the old drive and fill both memory channels with two Corsair XMS2 512M PC2 6400 sticks without a single flesh wound. Putting in the CPU was another issue however - I was short a pin.



Yeah... my old, to-be-recycled CPU was for Socket 939. This was a AM2 socket board - meaning it took 940-pin CPUs. Gah.

I paused for a few days and ordered a 2.1GHz AMD Athlon X2. It was a 65nm Brisbane core and only consumed 45W, so the lower thermals would serve a Myth box fairly well. Plus AMD chips are cheaper than avocados right now... it was an easy sell.



I wrangled the case together, put on some new thermal paste, and re-attached Shuttle's massive (did I mention its massive?) heat pipe for the CPU. Installed my old pcHDTV tuner card to receive HDTV channels from my local cable provider, then sealed everything up. I attached the barebones StreamZap Ir receiver via USB then did a openSUSE install with the MythTV repositories.

lircd actually worked without a hitch... the StreamZap didn't have any issues. Neither did the pcHDTV card - it worked out of the box as well. Things were going well, so I shoved the machine behind the TV, connected it via HDMI and went along my way.



At first things appeared to work well. Thanks to NVIDIA's nvidia-settings application I was able to effortlessly setup my 1080p LCD to work over HDMI. X configuration was TONS easier than with VIA's chipset - there it took me nearly 20-30 hours to get the monitor configuration correct for SVGA out. Of course it doesn't hurt that HDMI is just a DVI formfactor... but I digress.

No, the big pain was XvMC. With acceleration enabled, video would playback (either live or recorded) for anywhere between ten seconds to five minutes, then send X into a complete CPU spin. I'd suddenly have 100% usage on a single core and a complete lockup of X11. X had to be SIGKILL'd - repeatedly - before things would stop spinning out of control.

Luckily I bought a dual-core CPU so I could easily regain control. No matter now hard I tried, however, video acceleration just wouldn't do anything but hard lock MythTV.

Finally I gave up and just told MythTV to use the CPU for decoding. This worked acceptably, even with 720p streams. The CPU was beefy enough - it's a dual core, dual channel rig that has the bandwidth. Just a shame that neither NVIDIA nor VIA were able to provide a chipset that would allow accelerated MPEG2 playback in Linux. C'mon - is it really that bad?

Now things are recording and playing back just fine. The vsync is disabled right now - so I do have image tearing during high-motion decoding. But hopefully NVIDIA's next round of Linux drivers will fix XvMC, give me accelerated video and take all my worries away.

Chipped Chrome

VIA recently announced that they have opened their reference documentation for their GPUs and are even now actively working with the openChrome project. For me, however, it's too little too late.

I've finally grown tired of even trying to get accelerated video working on my VIA-based MythTV box. XvMC support is simply non-existent and accelerated anything just doesn't work. With standard 480i broadcast TV I had no problem being CPU-bound for MPEG2 decoding, but it just doesn't fly with 720p and a pcHDTV card. I throw in the towel.

I'm looking at what Shuttle has to offer instead with either an Intel, NVIDIA or AMD platform. It appears that the graphic chipset choices break down into either GeForce 8, Intel GMA X4500HD, Intel GMA 3100 or GeForce 7050PV. The best NVIDIA choice appears to be the 7050PV, as it seems to enjoy known XvMC acceleration on MythTV's feature matrix and some have even reported getting it to work in a dual-head environment. The Intel cards should theoretically offer great performance for the power and enjoy good Linux driver support due to Intel's great contributions to X.Org, however Myth's wiki seems to know painfully little about the Intel GMA's. As far as XvMC support goes, Intel's chipsets don't seem to have a great track record.

So GeForce 7050 seems to be the most sane choice for those who are tired of fisticuffs with xorg.conf. But wait! We have audio to worry about too. If I'm going with a Shuttle GeForce 7050, then it looks like I'm going with a Realtek ALC888DD. Here again, MythTV notes that yet another Intel chipset is a true pain to work with. Still, I noticed that the MythTV hardware database notes there was at least one other Shuttle user with a similar setup that was able to get things to work.

Weirdly enough, both of the GeForce 7050 Shuttle boxes I found were AMD boxes. Go figure...