[linux-dvb] Re: CI implementation question

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

On Friday 23 January 2004 16:16, Ralph Metzler wrote:
> Andrew de Quincey writes:
>  > CENELEC EN50221 implies that you can't write data to the CAM if it has
>  > data waiting to be read by the host. What have other people's
>  > implementations done if a user app attempts to write() data when it is
>  > not possible?
>  >
>  > I could cache the data to be written... I don't like this... the app
>  > might never read().
>
> Actually, driver and app have to read. The driver has to regularly poll for
> incoming data (usually no interrupt support) and the app has to answer
> to requests in time (or the connection with the CAM is lost) . So, the
> app has to read and write regularly.
> You will have to cache "read data" in any case.
> You can get around caching "write data" by blocking until no more
> reads are required if you want to.
>
> dvb_ca.c (based on the upper levels of the av7110 CA code) caches
> both. But in this case it had to because all data had to be moved
> through DEBI/AV7110. Still, you can use it for any link layer
> implementation which is driven by polling the CAM states.

Ahh cool, I didn't know about _that_ dvb_ca.c 'cos it isn't in the linuxtv 
linux-dvb tree. As you say, it looks like I can use that.

The dvb_ca.c :) that I've written luckily just contains all the generic bits I 
need that your dvb_ca.c doesn't (CAM initialisation, attribute parsing etc). 
I hadn't got on to writing the higher level link layer stuff yet.

It sounds like I should merge the two together. I assume you won't mind 
dvb_ca.c from your tree being added to the linuxtv tree, as long as licenses, 
copyrights etc are preserved?

Out of interest, if a CI module has two slots, and you're using read()/write() 
to communicate, how do you know which slot to talk to?

The ca.h in the linuxtv dvb-kernel implies that there is ONE ca device for 
each CI module, and you select the slot you want when you send the IOCTLS.... 
whereas if you're using read/write it would be more natural to create a 
seperate ca devive for each slot..?


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