[linux-dvb] Re: DVB-CA slot types

[Johannes Stezenbach <js@convergence.de>]

Andrew de Quincey wrote:
> ca.h defines the following types of CA slot device. I'm not sure what they're 
> meant to be:

One problem of this API is that it mixes two Conditional Access (CA)
things, namely Common Interface (CI) and built-in descramblers.

> CA_CI
> A "higher layer" interface. I don't know what this would correspond to... 
> maybe the EN50221 transport layer?

The original Technotrend av7110 firmware implemented a "high level"
CI protocol. You can see some (unused) leftover CI_ defines in av7110.h.

> CA_CI_LINK
> This sounds like it would correspond to the EN50221 link layer... i.e. the 
> data would consist of multiple interleaved fragmented packets.

I thought "link layer" and "transport layer" were synonymous...

> CA_CI_PHYS
> This sounds like it would be for hitting the EN50221 hardware directly (i.e. 
> twiddling the bits on the EN50021 physical interface).

AFAIK not implemented anywhere.

> CA_SC
> Simple smartcard reader.

AFAIK not implemented anywhere. IMHO it's also not useful to put
smartcard stuff into the DVB CA API.

> The linuxtv tree (not the metzler tree) also defines:
> CA_DESCR
> Which is a built in descrambler.

Implemented for av7110, but the public firmware does not support it
because some people think it makes pay tv hacking too easy...

> I can't have this quite right; the AV7110 CA driver in the metzler tree says 
> it is a CA_CI_LINK, yet it takes transport layer EN50221 packets.... from my 
> thinking (which is likely wrong) this should really have another type 
> CA_CI_TRANSPORT.
> 
> Can someone clear my confusion up please?

I hope I did.

> Also, in ca_caps, what are descr_num and descr_type meant to be? Are they only 
> meant to be set for certain types of interface, because there's certainly 
> nothing they correspond to at the level I'm looking at.

"total number of descrambler slots (keys)" means: You have one
descrambler, but it can descramble differnt PIDs with different keys.
And the descrambler can support different algorithms (ECD, NDS, DSS, ...).
In Europe it's usually ECD (European common descrambler, aka CSA Common
scrambling algorithm).

HTH,
Johannes


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