On 07/05/2012 11:10 PM, Mauro Carvalho Chehab wrote:
Em 05-07-2012 14:37, Bert Massop escreveu:
On Thu, Jul 5, 2012 at 5:05 PM, Antti Palosaari <crope@xxxxxx> 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.
We has already .get_frequency() which returns same information. It is
not currently used though few drivers implements it (wrongly). So I
don't see why this new callback should be added.
u32 actual_freq;
int afc;
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
ret = .get_frequency(fe, &actual_freq);
afc = c->frequency - actual_freq;
regards
Antti
--
http://palosaari.fi/
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