Re: DVB core enhancements - comments please?

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

Em 29-06-2012 02:03, Antti Palosaari escreveu:
> 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-infrastructure/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.

Why not? There's nothing at V4L2 API that limits it to analog, otherwise it couldn't
be used by digital cameras.

> 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.

The V4L2 API has everything to control receivers. What it doesn't have (and it doesn't make
sense to have, as such thing would just duplicate existing features at DVB API)
are the per delivery-system specific demodulator properties and PID filtering.

> 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?

Yes. There are lots of drivers that do that. There are even a few that allow to control the
frontend and demod via DVB API and to receive streams via V4L2 mmap or read API.

Regards,
Mauro