I'm working on cleaning up various AppleTV issues. I'm running the
mythic-beasts boot method under a 2.6.21.5 kernel with the AppleTV
and MacTel patches. The target is a standalone MythTV frontend able
to handle both SD and HD content. So far things are looking good,
with nvidia xvmc hardware decode, the AppleTV platform as sufficient
power to decode 1080i with 30 percent idle left over. There are some
issues that cause problems so the solution is not complete.
1) The network interface gets a large amount of overrun errors
when viewing HD content, I've tracked this down to the AppleTV cpu
running about 90 percent of the time in C3 state even with cpu at 70
percent. In C3 state, the response to interrupts is about 50 times
longer which results in network overrun errors. If I disable
processor.ko (acpi processor control), then I don't get network
errors. Naturally, some would say just run it this way but that's a
hack and I want to understand why it's sticking in C3 and never going
to C1, then fix the problem. The ability to idle down in power when
truly idle is important in this application.
From what I gather, most cpu power state problems are with
the inability to get to C3 for laptop battery life. This is the
reverse, I'm stuck in C3 with 10 percent usage in C2.
2) The pci-express root port/nvidia are running at X2 link
width. Under the AppleTV OSX, this link width is X16. So somehow the
pci-express link width gets limited to 2X width under linux but not
under OSX. Naturally this link width is important in mpeg2 decode
application especially when decoding HD content. My suspicion is that
this is somehow also related to being stuck in C3 power state. The
link width negotiation is handled by the two chipsets and it does not
see that the cpu is involved but maybe C3 power state also extends to
the chips sets.
Any suggestions or help would be appreciated.
Scott
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