[linux-dvb] Re: Proposal for new frontend architecture

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Wednesday 22 Sep 2004 21:36, Wolfgang Wegner wrote:
> On Wed, Sep 22, 2004 at 07:09:11PM +0200, Holger Waechtler wrote:
> > it's useful for other cards, too: usually the PLL/Synthesizer bandswitch
> > and Chargepump settings are completely board-dependent and by no mean
> > portable. Keeping them in the generic frontend code makes not much sense.
>
> i would not say so.
> IMHO, a "frontend" is a combination of Demod + PLL (nowadays together
> in a single tin box). There is nothing configurable by the board vendor
> except the I2C address.
>
> In my eyes (and that is how i saw it in a company's proprietary code,
> where it perfectly worked), a "frontend" consists of a demodulator driver,
> a PLL driver, some "glue" (or call it configuration - how the demod/AGC
> work together, crystal frequency, etc.) and wrapper to hold them together.
>
> I really see no reason why this needs to depend on (and thus pollute)
> a special i2c driver.

Have you looked at stv0299.c? It supports about 5 different tinboxes/boards, 
each of which uses the stv0299 chip. They all require different PLLs and have 
different settings. The code is spaghetti because of this.

The design is to share the implementation of demodulator drivers and not to 
have a seperate implementation for each board/tinbox - hence we need a way to 
allow it to be customised for each specific board/tinbox.

Anyway - there may not even be tin boxes in the long run - there's already a 
card on the market using that Philips single chip tuner (everything that used 
to be in the tin box on one piece of silicon). The demodulator is a seperate 
chip however.