Re: [PATCH 3/5] tda18218: fix IF frequency for 7MHz bandwidth channels

[Gianluca Gennari <gennarone@gmail.com>]

Il 03/04/2012 12:19, Antti Palosaari ha scritto:
> On 03.04.2012 03:44, Gianluca Gennari wrote:
>> Il 03/04/2012 00:40, Antti Palosaari ha scritto:
>>> On 03.04.2012 00:25, Gianluca Gennari wrote:
>>>> This is necessary to tune VHF channels with the AVerMedia A835 stick.
>>>>
>>>> Signed-off-by: Gianluca Gennari<gennarone@gmail.com>
>>>> ---
>>>>    drivers/media/common/tuners/tda18218.c |    2 +-
>>>>    1 files changed, 1 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/drivers/media/common/tuners/tda18218.c
>>>> b/drivers/media/common/tuners/tda18218.c
>>>> index dfb3a83..b079696 100644
>>>> --- a/drivers/media/common/tuners/tda18218.c
>>>> +++ b/drivers/media/common/tuners/tda18218.c
>>>> @@ -144,7 +144,7 @@ static int tda18218_set_params(struct dvb_frontend
>>>> *fe)
>>>>            priv->if_frequency = 3000000;
>>>>        } else if (bw<= 7000000) {
>>>>            LP_Fc = 1;
>>>> -        priv->if_frequency = 3500000;
>>>> +        priv->if_frequency = 4000000;
>>>>        } else {
>>>>            LP_Fc = 2;
>>>>            priv->if_frequency = 4000000;
>>>
>>> Kwaak, I will not apply that until I have done background checking. That
>>> driver is used only by AF9015 currently. And I did that driver as
>>> reverse-engineering and thus there is some things guessed. I have only 8
>>> MHz wide signal, thus I never tested 7 and 6 MHz. Have no DVB-T
>>> modulator either... Maybe some AF9015 user can confirm? Is there any
>>> AF9015&  TDA18218 bug reports seen in discussion forums...
>>
>> A friend has a AF9015+TDA18218 stick and told me that it works fine with
>> the patch (including VHF), but to be safe I will ask him to double check
>> with the current media_build tree, with and without the patch. In the
>> worst case, we can add a new parameter (or an array of parameters) for
>> the IF frequency to struct tda18218_config.
> 
> Public short datasheet [1], page 16, says default IFs are BW=8 MHz IF=4
> MHz, BW=7 MHz IF=3.5 MHz, BW=6 MHz IF=3 MHz. I suspect it still locks in
> some cases even IF is off-by 0.5 MHz for BW 7 and 8 but performance is
> reduced. So there is now something wrong, likely bug in the tda18218
> driver.
> 
> Could someone send me Windows sniff from success tune to 7 MHz BW channel?
> 
> [1] http://www.nxp.com/documents/data_sheet/TDA18218HN.pdf

Hi Antti,
the situation is a bit confusing.
The A835 always needed the IF frequency modification to tune VHF
channels, even with the famous Xgazza patch based on your old af9035 driver.
Instead, the af9015 was working fine in VHF band with the default 3.5MHz
IF frequency, until the recent rewrite of the tda18218 driver (which I
believe happened around kernel 3.0). After that, the af9015 started
working also with the 4MHz IF frequency (it's not clear if it still
works also with 3.5MHz, I will ask my friend to check this).
So probably you are right, there could be a bug in the tda18218 tuner
that was introduced recently.

A discussion on the A835 and VHF can be found on the Italian Ubuntu
forum (in Italian of course):
http://forum.ubuntu-it.org/index.php/topic,384436.msg3700932.html#msg3700932

Do you have any suggestion on the tool to sniff the windows driver?
Some time ago I tried SnoopyPro 0.22 and I was able to capture the first
~6000 packets of the A835 initialization, then it stopped capturing
before the first picture was displayed. Do you think it's enough? Do you
know any better free tool?

Regards,
Gianluca