Re: DVB core enhancements - comments please?

[Patrick Boettcher <pboettcher@kernellabs.com>]

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.

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.

regards,
--
Patrick.

Kernel Labs Inc.
http://www.kernellabs.com/