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fail to lock channels after upgrading to 4GB ram
PostPosted: Thu Nov 01, 2007 8:00 pm Reply with quote
ceckak
 
Joined: 01 Nov 2007
Posts: 4




Hi,

I've got an HD-5500 card which has been working great for nearly a year now in my 2GB system. I recently upgraded to 4GB of RAM and when I fired up mythtv, it failed to lock on any channels.

I found that if I add mem=2048M to my kernel options, mythtv starts working again. Given that the only thing that changed is the kernel's perception of how much RAM is available, I'm guessing that this is either a kernel bug and/or a driver bug. Since I haven't seen any other glaring problems with the full 4GB enabled, I'm inclined to think that the driver is to blame (possibly to do with the PCI card getting mapped to a virtual address outside of 32-bit address space?).

Is this a known issue, and better yet, is it already fixed in a current release?

A few details in case they're of interest:
CPU=Core 2 Duo
Chipset=Nvidia 680i
GPU=Nvidia 8800 (single x16 PCIe card)
No other PCI or PCIe cards
Kernel=2.6.18.8 SMP x86_64
Distro=openSUSE 10.2 X86-64

Thanks for any help!
Ken
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PostPosted: Fri Nov 02, 2007 5:54 pm Reply with quote
xyzzy
 
Joined: 12 Feb 2006
Posts: 225




It's certainly possible that it's a dma address range issue. From your description that's the first thing I would suspect.

The kernel and drivers you are using area over a year old. I know there were patches relating to creating a 32-bit dma area, and you may be running code too old to have the fix, which I think was somewhere around the 2.6.18 era. Or there could still be a bug in modern code with cx88 and 32-bit dma.

Mythtv is very high level test. Lower lever tests would be better. For instance, can you not get a lock with azap unless you pass mem=2048M? That would indicate a tuning issue that shouldn't have anything to do with dma.

The address of the memory mapped registers is normally set by the BIOS, so the mem parameter to the kernel shouldn't affect it. You could check with lspci -v and see if the cx88 gets the same memory address with and without the kernel mem limiting. This is not the memory used for DMA, which is where I think your problem is.
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PostPosted: Sat Nov 03, 2007 6:52 pm Reply with quote
ceckak
 
Joined: 01 Nov 2007
Posts: 4




Thanks for the reply. Got azap up and running and verified that it can get a lock irrespective of the mem= setting. I also compared the output of 'lspci -v' in both cases and the cx88 memory addresses were identical in both. If I understand you correctly, all of that points toward a dma bug.

So it sounds like my next step is to try building the latest driver sources and/or a new kernel and see if that makes a difference.

Ken
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PostPosted: Sat Nov 03, 2007 9:40 pm Reply with quote
ceckak
 
Joined: 01 Nov 2007
Posts: 4




I upgraded to openSUSE 10.3, which has kernel 2.6.22.5, and that seems to have resolved the problem. Mythtv is now locking channels correctly with the full 4GB of memory enabled.

Ken
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PostPosted: Sun Nov 04, 2007 1:51 pm Reply with quote
ceckak
 
Joined: 01 Nov 2007
Posts: 4




One more small follow-up on this. The 2.6.22 kernel in openSUSE 10.3 was an improvement, but still had problems. Specifically, I could lock on a channel in MythTV once, but if I dropped back to the main menu and then tried to go back to live TV again, MythTV would lock up and have to be forcefully killed. After some more testing, I again observed that booting with mem=2048M made this problem go away.

So now I've got a 2.6.23.1kernel installed (from openSUSE factory repository) and that seems to have resolved all problems. I can reliably and repeatedly lock onto channels in MythTV with all 4GB of memory enabled.

Ken
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fail to lock channels after upgrading to 4GB ram
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