[linux-dvb] RE : linux-dvb and Dektec [was: DVB API update]

Andrea Venturi a.venturi at cineca.it
Thu Oct 4 15:43:31 CEST 2007


ehi, what a thorough explanation..

maybe things are not all this black and white..

i wrote my first answer a bit quickly but now i'd like to give two more 
bits for added value!

Thierry Lelegard wrote:


> Also, as you pointed out, Dektec products can be either input, output
> or both. Their output products also include very nice modulators on
> PCI boards. I presently use a DTA-110T, a DVB-T modulator.
> Since linux-dvb is an input-only framework, it would address only
> part of Dektec products (and even part of a device in the case of
> a DTA-140).

indeed, the fact of the linux-dvb driver to be actually an input only 
framework for MPEG (TS/PS) stream it's beginning to fall a little short.

IMHO there are already a number of stuff and environment, old and newer, 
that need to be addressed, on linux, with an outgoing path for native 
MPEG streams.

historically there were two devices with such a capability:

- the Fully Fledged (nexus) cards with their MPEG2 decoder on board
- the ancient REALmagic Hollywood Plus

- actually there is also the MPEG2 decoder inside the iTVC15 / CX23415 
chip in the PVR350 card.. (ivtv driver not coping with it, i think..)

then, there's the big mess of video decoding of MPEG2 PES stream (SD/HD) 
and some acceleration for H264 stream inside the core of the recent GPUs 
(avivo and purehd marketing vaporware.. something from via and intel too..)

are we going to leave this feature available as a sub-set of the X 
driver or there's a place for a MPEG driver without the X?

i think for example to use-cases like the media center like myth-tv 
running with DirecFB..

in a bit different scenario, the embedded one, there are also devices 
natively decoding MPEG2 TS streams like:

- the PowerPc SoC inside some DVB SET TOP BOX as Dreambox and the 
DGStation CubeCafe (Vulcan and Pallas)
they do have actually a linux kernel running on the powerpc core but the 
decoding API are a bit "home made" and binary too (maybe thing are 

BTW we are a bit involved in a design of an open source java based 
middleware running on such HW so we are really using it and would prefer 
linux-dvb drivers for MPEG decoding..

- i really don't know how are coping with DVB decoding inside the other 
big player of the linux-based STB market, the Sigma Designs EM863x.

- and then there is the third player, STM ST710x who's running linux too 
with some DVB hack for decoding purposes..

IMHO plenty of situations where a linux dvb API for decoding stuff 
should/could be useful for the masses, because this generation of STBs 
are flooding our houses today or tomorrow, so we need and should have a 
way to hack them..

[..skipping lot of things about userland against kernel stuff..]

> Anyway, coming back to linux-dvb and Dektec, kernel drivers exist
> for both, just write userland code to access the one you want.

then i'd like to add some bits about the professional market using DVB 
ASI interfaces.

as someone already have told, there are plenty of DVB card producers; i 
can say out of my mind these: dektec, videopropulsion, optibase, 
dveo/computermodules, alitronika, bluetop (and other too..)

all these cards are of course running on linux today, but each with is 
own driver API..

i think only dektec is the one with open source driver openly available 
on the site and i know that some chinese are providing drivers with 
wrapper to mimic the dektec API.

that's how i see this market.

I don't know IF there's interest for the linux community at large to 
promote a unified driver for this technology..

in theory, the professional customers of such cards should be interested 
to get a single unified compatibility layer to escape the vendor lock 
in, BUT, if they are fine as they stay today, why the linux community 
should give them an hand?

i don't think we would get back something useful in the short term, but 
i'm open to hear other opinions too..


andrea venturi

> -Thierry 
> -----Message d'origine-----
> De : linux-dvb-bounces at linuxtv.org [mailto:linux-dvb-bounces at linuxtv.org] De la part de Andrea Venturi
> Envoyé : mercredi 3 octobre 2007 15:10
> À : linux-dvb
> Objet : Re: [linux-dvb] DVB API update
> Manu Abraham wrote:
>> Hi,
>> Simon Hailstone wrote:
>>> Hi All,
>>> If it sheds any light on the nature of DVB-ASI, there are Linux drivers
>>> available ( with source ) for the DekTec ASI adapters here :
>>> http://www.dektec.com/Products/LinuxSDK/Downloads/LinuxSDK.zip
>> If someone has the hardware, we can take a go at it.
> hi,
> here in Cineca, we are running an open source project called JustDvb-It,
> it's a DVB DSMCC carousel server for interactive television, you could
> grab it here:
>    http://www.cineca.tv/labs/mhplab/JustDVb-It%202.0.html
> as we need to interface broadcaster stuff like multiplexer (with DVB ASI
> interfaces), we use plenty of these Dektec card like DTA140 and so on..
> but for that purpose we found sufficient the driver provided by Dektec.
> it's a simple character device with some IOCTL..
> it should be not a tough task to implement a simple LinuxDvb driver, at
> least for the inbound card (but there's an outgoing path too..),
> but is this feature valuable? the best usage i can think of, is the
> dvbsnoop utility for analysis purposes..
> anyway i surely can test this driver, if it will spring out!
> bye
> andrea venturi

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