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

[Antti Palosaari <crope@iki.fi>]

On 13.12.2013 18:08, Hans Verkuil wrote:
> On 12/13/2013 04:42 PM, Antti Palosaari wrote:
>> On 13.12.2013 16:05, Hans Verkuil wrote:
>>> On 12/12/2013 06:22 PM, Antti Palosaari wrote:

>> I really appreciate that as simply has no enough knowledge from V4L2 API
>> and API changes are needed. I will try to list here shortly some SDR
>> devices in general level enough.
>>
>> ant = antenna
>> host = host computer, PC (SW modulator/demodulator)
>> ADC = analog to digital converter
>> DAC = digital to analog converter
>> amp = amplifier
>> mixer = "TX tuner"
>>
>> receiver:
>> ant <> RF tuner <> ADC <> bridge <> host
>> ant <>ADC <> bridge <> host
>> ant <> up-converter <> RF tuner <> ADC <> bridge <> host
>>
>> transmitter:
>> ant <> amp <> mixer <> DAC <> bridge <> host
>> ant <> mixer <> DAC <> bridge <> host
>> ant <> DAC <> bridge <> host
>>
>> Those are the used building blocks in some general view. ADC (DAC) is
>> most important hardware block, but RF tuner is also critical in practice.
>>
>> So what I understood, V4L2 API "tuner" is kinda logical entity that
>> represent single radio device, containing RF tuner, demodulator and so.
>> That same logical entity in DVB API side is frontend, which is mostly
>> implemented by demodulator with a help of RF tuner.
>>
>> So what is needed is to make V4L2 API entity (tuner I guess) that could
>> represent both ADC and RF tuner.
>
> Well, a V4L2 tuner represents the hardware that requires a frequency.
> Which for typical radio and TV devices means the RF tuner + demodulator
> combo. So externally you see only one tuner, but internally there are
> often two devices (tuner and modulator) that have to be controlled.
>
> For SDR you have an RF Tuner with a frequency and an ADC with a frequency,
> and the two frequencies can be set independently. So representing that
> as two tuners seems like a sensible mapping to me.

Correct. Both RF tuner and ADC are independent each others and both must 
be possible to adjust runtime.

Shortly, all-in-all, I will implement those as a tuner#0 is ADC and 
tuner#1 is RF tuner. Patches with corrections follow soon.

regards
Antti

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