Re: [PATCH RFC 4/4] v4l: 1 Hz resolution flag for tuners

[Antti Palosaari <crope@iki.fi>]

Hi Hans!

On 12.12.2013 09:55, Hans Verkuil wrote:
> On 12/12/2013 12:54 AM, Antti Palosaari wrote:
>> Add V4L2_TUNER_CAP_1HZ for 1 Hz resolution.
>>
>> Signed-off-by: Antti Palosaari <crope@iki.fi>
>> ---
>>   include/uapi/linux/videodev2.h | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>> index 6c6a601..1bac6c4 100644
>> --- a/include/uapi/linux/videodev2.h
>> +++ b/include/uapi/linux/videodev2.h
>> @@ -1349,6 +1349,7 @@ struct v4l2_modulator {
>>   #define V4L2_TUNER_CAP_RDS_CONTROLS	0x0200
>>   #define V4L2_TUNER_CAP_FREQ_BANDS	0x0400
>>   #define V4L2_TUNER_CAP_HWSEEK_PROG_LIM	0x0800
>> +#define V4L2_TUNER_CAP_1HZ		0x1000
>>
>>   /*  Flags for the 'rxsubchans' field */
>>   #define V4L2_TUNER_SUB_MONO		0x0001
>>
>
> I was wondering, do the band modulation systems (V4L2_BAND_MODULATION_VSB etc.) cover SDR?

There is no such modulations defined for SDR hardware level. SDR 
demodulation is done by software called DSP (digital signal processing) 
in host computer.

In ideal case, SDR receiver has only 1 property: ADC (analog to digital 
converter) sampling rate.

But as digital signal processing is very CPU intensive when sampling 
rates are increased, there is very often RF tuner used to down-convert 
actual radio frequency to low-IF / BB. Then ADC is used to sample that 
baseband / low-IF signal and only small sampling rate is needed => 
stream is smaller => DSP does not need so much CPU.

> Anyway, I'm happy with this patch series. As far as I am concerned, the next step would
> be to add documention and I would also recommend updating v4l2-compliance. Writing docs
> and adding compliance tests has proven useful in the past to discover ambiguous API specs.

I will do these at finally when I drivers and applications are tested to 
be working.

regards
Antti

-- 
http://palosaari.fi/