[mythtv-commits] Ticket #616: Wrong SNR/SIG values for some DVB cards

MythTV mythtv at cvs.mythtv.org
Tue Nov 8 12:43:11 EST 2005


#616: Wrong SNR/SIG values for some DVB cards
------------------------+---------------------------------------------------
 Reporter:  Adam Egger  |       Owner:  ijr 
     Type:  defect      |      Status:  new 
 Priority:  minor       |   Milestone:      
Component:  mythtv      |     Version:  head
 Severity:  medium      |  
------------------------+---------------------------------------------------
The signal monitor shows wrong values for several DVB card types. My
 Airstar2 (b2c2_flexcop_pci) shows 49% for all channels, which makes the
 antenna adjustment mode and the values the signal monitor shows in LiveTV
 quite unusable for several users.
 Btw, the value shown in Kaffeine is always correct.

 Daniel's comment on this:
 ----
 {{{
  65535*0.23 - 32768 => -17695[[BR]]
  65535*0.49 - 32768 => -655.85
 }}}
 -17695 +/- 700, and -655.85 +/- 700 are the values I'd expect the
 driver is giving for signal.

 So I found your logging on the mailing list...
 {{{
 2005-10-23 15:26:22.911 SIGNAL: SNR (0)
 2005-10-23 15:26:22.966 SIGNAL: SIG (-157)
 2005-10-23 15:26:22.967 SIGNAL: SNR (0)
 2005-10-23 15:26:23.022 SIGNAL: SIG (-203)
 2005-10-23 15:26:23.023 SIGNAL: SNR (-31355)
 2005-10-23 15:26:23.085 SIGNAL: SIG (-197)
 2005-10-23 15:26:23.085 SIGNAL: SNR (-23131)
 }}}
 Ok, the problem here is that MythTV tries to detect when the signal
 value is bogus, and use the SNR, in your case the driver is reporting
 a signal value that doesn't appear bogus to MythTV. Look in tv_play.cpp
 at TV::UpdateOSDSignal(). You will see that a bogus signal value is
 considered to be anything in the vicinity of 0% or 100%, in your case
 a value of 23% or 49% could be a perfectly valid value.

 There are three routes to fixing this: make MythTV better at detecting
 broken drivers, fix the DVB drivers for the card you are using to
 report a valid signal value (even if it is just a re-branded SNR), or
 add yet another configuration setting to MythTV. I'd prefer one or
 both of the first two solutions.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/616>
MythTV <http://www.mythtv.org/>
MythTV


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