[mythtv-users] recommend PCI DVB-T Tuner Card?

[Devin Heitmueller]

On Thu, May 13, 2010 at 11:28 AM, Ed W <lists at wildgooses.com> wrote:
>
>>>> And be prepared to get a powered USB hub, since
>>>> even a single tuner draws pretty close to the 500ma limit while
>>>> streaming (thereby hitting the power limit on a single port).
>>>>
>>>
>>> Same as above. I have 3 USB devices (2 single and one double tuner)
>>> running off
>>> the ports on my mobo.
>>>
>>
>> You've probably got a motherboard that provides 500ma *per* port.
>> Again, you're lucky enough to have ended up with hardware that is well
>> designed.  You shouldn't assume that everyone will be so lucky.
>>
>
> Hi Devin,  I wonder if you can help.  OK, I've set myself up for failure
> here by hoping to switch to USB DVB-T cards, and last week on my test Atom
> itx board I successfully plugged in 3x PEAK dual dvb-t tuners and all was
> well!  The ATOM was under powered so I just bought a new Asus board with a
> Core2 3Ghz on it and now even a single DVB-T usb card is giving me big
> picture breakup every few seconds...
>
> However, the symptoms are more complex than they seem.  Help on diagnosing
> appreciated:
>
> - Older recordings on the same card, but recorded on older MB are fine
> - Newer live tv *starts out* perfect, but breaks up only after a couple of
> minutes of viewing...  If I quit Livetv and go back in I get a few mins
> glitch free! In fact re-tuning to the same channel stops the breakup for
> another few minutes...
> - Some recordings are perfect, I can't figure out the correlation though?
> - Swapping USB port hasn't obviously affected things
> - For long periods of time femon is not showing the slightest error.  I just
> turned on a recording and after 2-3 mins the picture started breaking up,
> during that time BER remained zero, as did uncorrectable errors. Retuning
> stopped the breakup for another few mins and then it restarted...
> - Antenna has been working well for several years and is amplified with good
> quality coax
>
> I am unsure how to debug this properly.  Can anyone recommend some settings
> I might fiddle with, or tools that could help me monitor this?  Are there
> kernel settings such as APIC/ACPI that affect usb timings and might improve
> or worsen things?
>
> Do the above symptoms even fit with an obvious cause?  It's as though the
> problem is within Myth rather than the usb card?  However, the change is due
> to swapping motherboard, so it seems likely to be more a function of USB
> behaviour or something that the computer is doing which is affecting
> interrupts or latency or something causing these glitches?  (Actually I did
> change HEAD version of mythtv thinking about it, so it could be mythtv code,
> but I don't see anyone else commenting on recording gremlins?)
>
> There used to be some signal strength monitoring code, however, I can't see
> anything obvious on the backend that I can enable to give me some stats on
> what I'm recording.  I obviously haven't turned on the right logging on the
> frontend because I'm not yet seeing logs about the cause of these decoding
> glitches?  Any tips on how ot turn up the logging in Mythtv?
>
> I'm really very keen to try and make the USB cards work, baffled as to how
> to debug this further though?  Google gives me surprisingly little on
> toggling kernel / MB params to try and tweak this?
>
> Thanks for any help?

Hello Ed,

Sorry for the delayed response.  I really need to setup my Google
filters to highlight emails where I'm actually on the TO address
(otherwise it gets lost among all the other list traffic).

Do you have any other devices plugged into the USB (for example, a USB
hard drive).  It's possible there is bus contention which results in
packet loss.

Which tuner product is it?  Knowing what product will tell us what
chips it contains, which might offer some insight.

Also, do you *ever* see the SNR/BER count change?  Some of the tuners
*always* report zero because the functionality is unimplemented (and
yes, this is a violation of the Linux DVB spec).  So you should unplug
your antenna for a few seconds and make sure that the SNR/BER counts
actually work.

You may also which to run top when you are seeing the problem, and
make sure there is not some batch job coming around during recording
which is starving the CPU.

It's possible there is a bug in the tuner driver which causes the
tuning to drift over time.  Are you sure this exact tuner product
works correctly in your old system?

Devin

-- 
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com