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/
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