[linux-dvb] TDA8290/TDA8275 with LNA (was: Support for pre-amplifier?)

Hartmut Hackmann hartmut.hackmann at t-online.de
Sun Feb 25 01:35:05 CET 2007


Hi, Nico

Nico Sabbi schrieb:
> Hi
> I've just noticed that in your tree there's support for the
> pre-amplifier of some Philips cards.
> Does the Lifeview Trio already use your new code? Or do I need to add
> support for it?
> 
I copy this to the mailing lists because i think this is interesting
for more people.
First: the code went to mainstream yesterday.

Then i should give some explaination of what this is about:
Many recent cards with the TDA8275a silicon tuner have a preamplifier
(LNA) in front of the tuner chip. It is *not* inside the chip, and
since it costs some cents, it will not be on all recent cards.
This LNA needs to be controlled by the driver. I know about 3 variants
how this is done, currently, the driver doesn't detect the variant
automatically. So there is a new entry for the board configuration in
saa7134-cards.c. Possible values are:
.tuner_config   = 0, : no LNA present. This is the default
.tuner_config   = 1, : with LNA. This config is used on the Pinnacle 310i
.tuner_config   = 2, : with LNA. This is used on the Philips Tiger-S reference
                                 design and probably on most others.
.tuner_config   = 3,   with LNA. The new variant. Not sure who uses this.
There is an entry with the same meaning for the tda10046 configuration
in saa7134-dvb.c
I should add that the configurations 1 and 3 are untested. I am quite
sure that 1 is right but not so sure about config 3.

The configuration can be read from the eeprom if the card works with
the stock Philips drivers. In all other cases (yours), you need to
find it by try and error.
I need your help and feedback to get this completed:
Please load the tuner driver with the debug=1 option
so either
modprobe tuner debug=1
or - if the driver is autoloaded -
options tuner debug=1
in /etc/modprobe.conf.local (distribution depending)
you will find new messages in the kernel log
(a "xterm -e tail -f /var/log/messages &" helps)
"setting LNA to high gain"
and
"AGC2 gain is: xx"
The range is from 0 to 10, a higher value means less signal amplitude.
The upper message only occurs if tuner_config is not 0.

-Tune to a station and write down the value for AGC2
- set tuner_config to the value to test and recompile and relod the
  driver. If you now try to tune to the same station, the following
  is expected: First the driver reports:
  "setting LNA to high gain"
  then the tuner goes on. If things are right, the driver will either
  report:  "setting LNA to low gain" or a lower value for AGC2.
If this occurs, your card has an LNA and you have the right configuration.
I am not absolutely sure with config 3. There might be the situation
that you see the effects of the LNA but you see a "unstable brightness"
or have humming sound. In this case, you need to altenate config 2 and 3
and get in contact with me.

Good luck and don't forget to report the results

 Hartmut



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