Re: [PATCH 3/3] [media] tuner, xc2028: add support for get_afc()

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 05-07-2012 14:37, Bert Massop escreveu:
> On Thu, Jul 5, 2012 at 5:05 PM, Antti Palosaari <crope@iki.fi> wrote:
>>
>> On 07/05/2012 05:16 PM, Mauro Carvalho Chehab wrote:
>>>
>>> Implement API support to return AFC frequency shift, as this device
>>> supports it. The only other driver that implements it is tda9887,
>>> and the frequency there is reported in Hz. So, use Hz also for this
>>> tuner.
>>
>>
>> What is AFC and why it is needed?
>>
> 
> AFC is short for Automatic Frequency Control, by which a tuner
> automatically fine-tunes the frequency for the best reception,
> compensating for small offsets and oscillator frequency drift.
> This is however done automatically on the tuner, so its configuration
> is read-only. Aside from being a "nice to know" statistic, getting
> hold of the AFC frequency shift does as far as I know not have any
> practical uses related to properly operating the tuner.

AFC might be useful on a few situations. For example, my CATV operator
still broadcasts some channels in both analog and digital. The analog
equipment there doesn't seem to be well-maintained, as some channels have
frequency shifts or have some other artifacts. Still, analog broadcast
is useful for me to test drivers ;)

Anyway, adjusting the channel tables to consider that offset shift help
to tune them a little faster and/or get a better quality by letting the
PLL to work closer to the pilot carrier.

Regards,
Mauro