[mythtv-users] DVB OSD Signal always 0%

Mike Isely isely at isely.net
Wed Jun 3 01:17:09 UTC 2009

This answer Roger quoted below is not correct.

Roger had asked me on the pvrusb2 driver list why the driver's sysfs 
interface was not reporting signal strength, NOT why mythtv was doing 
this.  The quoted text below comes from my answer to the question about 
sysfs.  The post can be found here:


In the context of the sysfs interface, my answer is correct: When in dtv 
mode signal strength is not reportable through V4L or the driver's sysfs 
interface because the pvrusb2 driver is not in control of the tuner.

But mythtv can get signal strength information via DVB - that is after 
all how it's going to work when talking to a normal DVB device.  The 
pvrusb2 driver when in dtv mode effectively *is* a normal DVB device.  I 
don't do anything special in the driver to help or hinder reporting of 
that signal strength in this case - it's all up to the DVB core.  I have 
to think that DVB is probably getting this right unless there's a bug in 
the driver that corresponds to the tuner chip being used by the HVR-1950 
(there have been some recent issues).  If DVB is getting this right, 
then I can't explain this.

What I can explain is that the explanation below is not relevant for the 
question that was asked on this mythtv-users thread.


On Tue, 2 Jun 2009, Roger wrote:

> On Wed, 2009-06-03 at 08:58 +1200, Nick Rout wrote:
> > I think some cards, or some drivers perhaps, do not report such
> > statistics correctly.
> >From the maintainer of pvrusb2 ... 
> "When you are playing a dtv stream, the pvrusb2 driver has very very 
> little control over what is going on.  This because the DVB 
> infrastructure prefers to "own" the hardware while in dtv mode.  All the
> pvrusb2 driver does really here is pass through the mpeg data stream and
> otherwise stay out of the way of DVB.  So any kind of status info while 
> in dtv mode really has to come from the DVB core not the pvrusb2 driver.
> Thus the sysfs interface and ALL of the V4L interface is effectively 
> unusable once a DVB application has taken the reigns.  What 
> ctl_signal_present only will tell you is the status when you are in 
> television or radio mode not dtv mode.
> ...I am limited to with the DVB internal architecture as it currently
> stands.  There are a few ideas being tossed around that might mitigate
> this, but at the moment they are just ideas (actually really only one
> idea)."
> (Hence, it's not a driver issue but an in-kernel V4L/DVB issue)


Mike Isely
isely @ isely (dot) net
PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8

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