Re: DVB core enhancements - comments please?

[Antti Palosaari <crope@iki.fi>]

On 06/29/2012 02:24 PM, Patrick Boettcher wrote:
> On Friday 29 June 2012 08:03:16 Antti Palosaari wrote:
>> On 06/29/2012 07:32 AM, Mauro Carvalho Chehab wrote:
>>> Em 27-06-2012 21:33, Antti Palosaari escreveu:
>>>> SDR - Softaware Defined Radio support DVB API
>>>> --------------------------------------------------
>>>> *
>>>> http://comments.gmane.org/gmane.linux.drivers.video-input-infrastructu
>>>> re/44461 * there is existing devices that are SDR (RTL2832U "rtl-sdr")
>>>> * SDR is quite near what is digital TV streaming
>>>> * study what is needed
>>>> * new delivery system for frontend API called SDR?
>>>> * some core changes needed, like status (is locked etc)
>>>> * how about demuxer?
>>>> * stream conversion, inside Kernel?
>>>> * what are new parameters needed for DVB API?
>>>
>>> Let's not mix APIs: the radio control should use the V4L2 API, as this
>>> is not DVB. The V4L2 API has already everything needed for radio. The
>>> only missing part ther is the audio stream. However, there are a few
>>> drivers that provide audio via the radio device node, using
>>> read()/poll() syscalls, like pvrusb. On this specific driver, audio
>>> comes through a MPEG stream. As SDR provides audio on a different
>>> format, it could make sense to use VIDIOC_S_STD/VIDIOC_G_STD to
>>> set/retrieve the type of audio stream, for SDR, but maybe it better to
>>> just add capabilities flag at VIDIOC_QUERYCTL or VIDIOC_G_TUNER to
>>> indicate that the audio will come though the radio node and if the
>>> format is MPEG or SDR.
>> SDR is not a radio in mean of V4L2 analog audio radios. SDR can receive
>> all kind of signals, analog audio, analog television, digital radio,
>> digital television, cellular phones, etc. You can even receive DVB-T,
>> but hardware I have is not capable to receive such wide stream.
>>
>> That chip supports natively DVB-T TS but change be switched to SDR mode.
>> Is it even possible to switch from DVB API (DVB-T delivery system) to
>> V4L2 API at runtime?
>
> It could be possible that neither the DVB-API nor the V4L2 API is the right
> user-interface for such devices. The output of such devices is the
> acquisition of raw (digitalized) data of a signal and here signal is meant
> in the sense of anything which can be digitalized (e.g.: sensors, tuners,
> ADCs).
>
> Such device will surely be have a device-specific (user-space?) library to
> do the post/pre-processing before putting this data into a generic format.

Generic format for SDR is Complex. I had some plans to do that 
conversion inside Kernel.

> That said, IMO, the rtl-sdr driver should sit on the DVB-API. Maybe V4L2
> provides a device-specific control path (to configure the hardware) if not
> somewhere else, or something new needs to be created.

For me DVB API sounds very easy to implement. At the minimum only new 
delivery system and conversion to Complex. If you skip stream conversion 
and add only new delivery system, it is just single line of code to DVB 
frontend (at the most simplest case).

V4L2 sounds hard for me since I have never done anything with it. But 
surely I can implement it as V4L2 too if it is correct way and there is 
someone who could give some tips how to proceed.

regards
Antti

-- 
http://palosaari.fi/