[vdr] Dual DVB-S2 Tuner cards

Andre vdr at dinkum.org.uk
Fri Jun 25 16:21:43 CEST 2010

On 25 Jun 2010, at 13:43, James Courtier-Dutton wrote:

> 2010/6/25 Andre <vdr at dinkum.org.uk>:
>> On 19 Jun 2010, at 09:00, Goga777 wrote:
>>> which problems do you have with hvr4000 ???
>> I get semi random glitches in the recordings that the Satix doesn't get also my Nova S+ (before it packed up last week) doesn't get the glitches.
>> It's significantly better since the upgrade to Ubuntu 10.04, even though I was running 2.6.33 kernel on 9.04 and latest v4l drivers.
>> My next debugging step will be to ditch my Nova T500 for a while, after some reading on the linux-media list it seems this driver doesn't play nicely with busy interrupts and with three tuner cards and six disks this machine is busy.
> I would be surprised if one DVB card had more or less glitches than another.

Well it seems to be the case, the feed I have is from an oversized dish on a communal system, no dropouts even in heavy rainstorms, I specced it that way :-) Also I checked that the dish alignment was central to the constellation (figure 8 paths) rather than lined up on only one bird as seems to be consumer industry norm! I work in Satellite TV in case you hadn't guessed, although more uplinks and fiber feeds than downlinks.

I have 4 feeds, there seems to be no variation is signal strength between them, if I record from DVBS2 on the Satix card I get the odd glitch at the start of the recording, in the first 30 seconds and maybe one glitch in every other 1 hour programme. If I record with the HD S2 or HVR4000 I get 5 or 6 glitches in a 30 minute programme, actually the HVR 4000 seemed worse than the HD S2 but it's ok now I moved it to a different PC, different feed for a different satellite so can't really compare them now. If I record a DVBS transmission BBCHD or ITVHD on my Nova S+ it's fine, rarely ever a glitch, if I use the Satix, the same, the HD S2 gives me 5 or 6 a hour again.

I've seen the same problem with very little variation across VDR, MythTV and TV Headend on the same hardware. If I have only a HVR 4000 or HD S2 in the PC it seems to work with almost no glitches.

Oh and I'm only talking about HDTV, I record very very little SDTV, the system records about 6 or 7 hours of HDTV a night, three simultaneous recordings is common, of course I only watch a small amount of this :but this is what PVR software is all about :-)

> Glitches on DVB are more likely cause by bad reception so receiver
> sensitivity and worse S/N ratio would be the most likely causes.
> DVB satellites move around the sky in a figure of 8 shape, so
> depending on where your dish is pointing, the signal signal strength
> might vary over time.
> Was the S/N ratio the same on both cards?

Haven't checked S/N but I'm not convinced there is any comparability in the S/N stats across different cards, the figures look very untrustworthy and reading the linux-media list suggests the stats across drivers are not to be trusted.

The glitches are fairly significant, several frames are missing, a gop or two is affected, in between glitches not a single error, symptoms the same on FTA or encrypted. There doesn't appear to be any corresponding dmesg at the time of the glitches.

> It might be that the hard disks are causing the problem or the filesystem.

Quite likely, I have 6 sata disks in the main machine, ICH6 & SIL24, Hitachi & Samsung 1TB & 1.5TB drives, I have had significant problems with sata disconnects under Ubuntu 9.04 but no problems at all since going to 10.04.

> Which file system are you using?

EXT3 on md raid 1 for /boot
XFS on LVM on md raid1 for /, /home & /var
XFS on separate LVMs for 4 video storage mounts.

> I know rieserfs is particularly bad for low latency application.

Any other suggestions gratefully received :-) I'm considering a motherboard swap in the main machine.

> James
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