DVB reliability problems

DVB reliability problems

[Tony Houghton]

Hi,

I've been having problems with my DVB receivers lately. I'm not sure
whether the problem is in the receivers or their firmware, or Linux.
Some symptoms point to the card, some point to Linux (because they
should try to prevent the system from hanging even with bad hardware
if the hardware is peripheral?). Perhaps the majority of USB DVB
receivers are actually useless junk?

I'm trying to develop a good DVB PVR, but if I can't fix these
problems there's not much point in continuing. I hope someone can
offer some suggestions on what's causing the problems and/or how I can
diagnose them better, and hopefully get things fixed.

Frequently one of them will stop working. The main symptom is that
after tuning they fail to get a signal. If I don't "fix" it asap by
power cycling the PC (reboot seems to be inadequate) the situation
seems to escalate until the entire system hangs, either when trying to
use the receiver or at shutdown.

The problems seem to have developed or exacerbated mainly since I
started using an Intel NUC as my PVR and therefore had to replace my
DVBSky PCI-E DVB-S2 card with a USB TeVii S662 DVB-S2. After a while
it started exhibiting the above symptoms with increasing frequency.
When it got to daily problems I returned it under warranty and
replaced it with a DVBSky S960 V2. IIRC it has the same Montage
chipset as the TeVii; this seems to be the only chipset commonly
available in USB DVB-S2 devices. At first, the change of device seemed
to cure the issue, but that's started doing the same thing too.

Meanwhile I've also been using a DVB-T2 USB stick. At first I had a
Pinnacle PCTV 290e. That worked quite well until it seemed to fail
completely (not even detected by lsusb). I replaced it with a
"Geniatech MyGica DVB-T2/T USB" which I think uses the si2168/si2157
modules. This one's also unreliable.

-- 
TH

Re: DVB reliability problems

[Hans Petter Selasky]

On 7/2/21 7:06 PM, Tony Houghton wrote:
> Hi,
> 
> I've been having problems with my DVB receivers lately. I'm not sure
> whether the problem is in the receivers or their firmware, or Linux.
> Some symptoms point to the card, some point to Linux (because they
> should try to prevent the system from hanging even with bad hardware
> if the hardware is peripheral?). Perhaps the majority of USB DVB
> receivers are actually useless junk?
> 
> I'm trying to develop a good DVB PVR, but if I can't fix these
> problems there's not much point in continuing. I hope someone can
> offer some suggestions on what's causing the problems and/or how I can
> diagnose them better, and hopefully get things fixed.
> 
> Frequently one of them will stop working. The main symptom is that
> after tuning they fail to get a signal. If I don't "fix" it asap by
> power cycling the PC (reboot seems to be inadequate) the situation
> seems to escalate until the entire system hangs, either when trying to
> use the receiver or at shutdown.
> 
> The problems seem to have developed or exacerbated mainly since I
> started using an Intel NUC as my PVR and therefore had to replace my
> DVBSky PCI-E DVB-S2 card with a USB TeVii S662 DVB-S2. After a while
> it started exhibiting the above symptoms with increasing frequency.
> When it got to daily problems I returned it under warranty and
> replaced it with a DVBSky S960 V2. IIRC it has the same Montage
> chipset as the TeVii; this seems to be the only chipset commonly
> available in USB DVB-S2 devices. At first, the change of device seemed
> to cure the issue, but that's started doing the same thing too.
> 
> Meanwhile I've also been using a DVB-T2 USB stick. At first I had a
> Pinnacle PCTV 290e. That worked quite well until it seemed to fail
> completely (not even detected by lsusb). I replaced it with a
> "Geniatech MyGica DVB-T2/T USB" which I think uses the si2168/si2157
> modules. This one's also unreliable.
> 

Hi,

I've seen problems with DVBSky USB devices when using the CAM slot, 
typically during bad signal conditions. Seems to be an issue with the 
decoder card. Bought a new antenna, and the problems were significantly 
reduced!

--HPS

Re: DVB reliability problems

[Tony Houghton]

On Fri, 2 Jul 2021 at 19:43, Hans Petter Selasky <hps@selasky.org> wrote:

> Hi,
>
> I've seen problems with DVBSky USB devices when using the CAM slot,
> typically during bad signal conditions. Seems to be an issue with the
> decoder card. Bought a new antenna, and the problems were significantly
> reduced!

Thanks for replying. I don't use any CAMs though, so something else
must be causing my problems.

-- 
TH

Re: DVB reliability problems

[Mauro Carvalho Chehab]

Em Fri, 2 Jul 2021 18:06:26 +0100
Tony Houghton <h@realh.co.uk> escreveu:

> Hi,
> 
> I've been having problems with my DVB receivers lately. I'm not sure
> whether the problem is in the receivers or their firmware, or Linux.
> Some symptoms point to the card, some point to Linux (because they
> should try to prevent the system from hanging even with bad hardware
> if the hardware is peripheral?). Perhaps the majority of USB DVB
> receivers are actually useless junk?
> 
> I'm trying to develop a good DVB PVR, but if I can't fix these
> problems there's not much point in continuing. I hope someone can
> offer some suggestions on what's causing the problems and/or how I can
> diagnose them better, and hopefully get things fixed.
> 
> Frequently one of them will stop working. The main symptom is that
> after tuning they fail to get a signal. If I don't "fix" it asap by
> power cycling the PC (reboot seems to be inadequate) the situation
> seems to escalate until the entire system hangs, either when trying to
> use the receiver or at shutdown.

This is a very weird behavior. Never saw anything like that happening
with an upstream Kernel. Are you using anything else like some
proprietary driver or dvbloopback?

Are there any messages printed by the Kernel when the machine starts
to die?

If you're not using dvbloopback or a proprietary driver, I would
suspect that your PC hardware could have some issue... perhaps it
is overheating or there are some power issues on it, as it doesn't
make much sense that a fail to tune would cause a system hang.


Thanks,
Mauro

Re: DVB reliability problems

[Tony Houghton]

On Fri, 2 Jul 2021 at 21:05, Mauro Carvalho Chehab
<mchehab+huawei@kernel.org> wrote:

[System hanging after DVB receivers fail]

> This is a very weird behavior. Never saw anything like that happening
> with an upstream Kernel. Are you using anything else like some
> proprietary driver or dvbloopback?
>
> Are there any messages printed by the Kernel when the machine starts
> to die?
>
> If you're not using dvbloopback or a proprietary driver, I would
> suspect that your PC hardware could have some issue... perhaps it
> is overheating or there are some power issues on it, as it doesn't
> make much sense that a fail to tune would cause a system hang.

It's an ARch Linux system, and everything is vanilla. I get the
impression the hanging is caused by blocking I/O on the device
descriptors, but at least on the last time I happened it hung on
shutdown after I had stopped all programs using the devices. So one of
the modules could have been still holding the bad descriptor open, but
I got the impression more than 90 seconds had passed before I pulled
the plug, so systemd should have killed it by then, if that was what
was blocking the shutdown.

Another symptom I've seen is that it can cause tvheadend to busy loop
with 100% on one CPU core, and become extremely slow to respond on its
web server and to shut down, so overheating is a remote possibility.
But as it's only affecting one core out of four, it's unlikely.
Perhaps too much power is being drawn from the USB subsytem, but I
would have thought Intel would have made sure their NUC PSUs are good
quality.

Years ago I saw something similar with a cheap Chinese IR receiver for
a Windows Media remote control, it would make the system hang when
plugged in. That may have been so long ago that it was kernel 2.x, let
alone 3.x.

Next time I notice the problem starting I'll check the logs straight
away, but the trouble with system hangs is that they tend to destroy
their evidence. I'll also see if unplugging the troublesome device and
re-inserting it without rebooting is enough to revive it, because that
could provide a better idea of hardware vs driver issues.

-- 
TH