[linux-dvb] Re: V4 API proposal

[emard@softhome.net]

> I think you misunderstood something. One major goal is to use the dvb
> api in many set top boxes. Those do have very specialized hardware. This
> hardware e.g. allows the cpu to operate at a low frequency and therefore
> those boxes may be designed cool and silent enough to be a nice thing to
> enjoy.
I did not misunderstood. I want to simplify the things. UNIX is
univesal tool and needs simple API. Can't support every peculiar
hardware acceleration chip. It must be limited to a reduced
functionality, simple and clean to implement and stable to run. 
Good driver doesn't need to support every single feature, but what it
supports it should do right. 
Look at the video cards. Linux xfree86 X server doesn't support every
nvidia 3D acceleration feature but I don't care. Draws X fast enough
and can view budget DVB with mplayer without frame drop. 
There's vendor-specific nvidia X server supporting some 3D acceleration,
but still not everything. Who wishes to play maximum 3D can boot MS windiws. 
> Btw. as far as I am informed it is not legal (at least in most
> countries) to implement a dvb descrambler in software which makes it far
> from legal to implement it as open source software. Additionaly this
> would require to do some stuff which is typical for CAMs in software,
> which is definitely not what conditional access system manufacturers
> would like you to do.
Laws will change according to the common practice. It's just a
question of time, and that depends on us, the consumers, how long
can we stand without something. 
> See above. They are too hot and their fans are too noisy. PCs don't fit
> into a family's living room. Using DVB on little endian machines (I
> guess you only thought of typical x86 systems) is a mess. DVB suits much
> better into big endian machines.
This is true, moving parts like fans are never good to have in any
electronic equipment. Noise and prone to failures. 
> > Remember analogy with expensive early soundcards with 
> > onboard sound FX/midi/mpeg dsp chips, 
> > compared to simple dummy 16 bit wav output 'dsp' chips.
> Most people still have amplifiers, cd players, dvd players, tuners etc.
> Not every device in the world does fit into a PCI slot.
I know...However I got rid from my last CD player 2 years ago and
last year I finally trashed my 12x 2N3055 bipolar transistor amplifier.
So I don't have any of such items left. I have seen
article about upcoming 64 BIT AMD based motherboards will have
ONBOARD 3x VACUUM TUBES amplifier :)). 
> > Nowdays we all have simple dsp wav output cards while
> > mp3 decompression is done by the software.
> ...and mp3, mpeg2 audio, ac3 etc. decompression in hardware.
Linux kernel API can't support it in a well defined way.
There is software that does mp3  playing on any card, regardless if
card has onboard hardware or not. 
getting back to V4 API, special hardware like av7110 should export a
so called vendor-specific list of capabilities to the userspace application.
DVR as application is av7110 specific anyway. 
so given the capabilities list, application will know what it can expect
from the hardware and what specific hardware can't do. 
Kernel API just can't cover every particular hardware design because
some of them will surely contradict with the other. 
In the near future of PC desktop multimedia, majority of the DVB cards will
support just budget type features. 
V4 driver API should allow budget functions be expanded
with mpeg/ci external (binary?) modules and/or userspace
daemons that replace av7110. 
Thus making a driver having every feature DVB-S and even more
flexibility, while the hardware is completely abstracted from
recorded/viewer application's point of view. 
In the STB, onboard hardware mpegs and low power CPUs can
still be used with with such API where mpeg/ci software modules
is replaced by kernel driver utilizing the hardware features, maybe
it would require other adaptations of the DVB layers and of course
it must have reduced functionality compared to software mpeg/ci
due to limitations of hardware.
That's not a problem becuse STB will have single and fixed
application built-in. 
Emard 

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