[linux-dvb] DVB-S2 / Multiproto and future modulation support

Steven Toth stoth at linuxtv.org
Thu Sep 11 04:59:26 CEST 2008

hermann pitton wrote:
> Hi,
> Am Mittwoch, den 10.09.2008, 21:00 -0400 schrieb Steven Toth:
>> Christophe Thommeret wrote:
>>> Le Thursday 11 September 2008 00:59:31 Andreas Oberritter, vous avez écrit :
>>>> Hans Werner wrote:
>>>>>> So applications could know that these 2 frontends are exclusive.
>>>>>> That would not require any API change, but would have to be a rule
>>>>>> followed by
>>>>>> all drivers.
>>>>> Yes, if we keep to that rule then only frontends which can operate truly
>>>>> simultaneously should have a different adapter number.
>>>> An adapter refers to a self-contained piece of hardware, whose parts can
>>>> not be used by a second adapter (e.g. adapter0/demux0 can not access the
>>>> data from adapter1/frontend1). In a commonly used setup it means that
>>>> adapter0 is the first initialized PCI card and adapter1 is the second.
>>>> Now, if you want a device with two tuners that can be accessed
>>>> simultaneously to create a second adapter, then you would have to
>>>> artificially divide its components so that it looks like two independant
>>>> PCI cards. This might become very complicated and limits the functions
>>>> of the hardware.
>>>> However, on a setup with multiple accessible tuners you can expect at
>>>> least the same amount of accessible demux devices on the same adapter
>>>> (and also dvr devices for that matter). There is an ioctl to connect a
>>>> frontend to a specific demux (DMX_SET_SOURCE).
>>>> So, if there are demux0, frontend0 and frontend1, then the application
>>>> knows that it can't use both frontends simultaneously. Otherwise, if 
>>>> there are demux0, demux1, frontend0 and frontend1, then it can use both
>>>> of them (by using both demux devices and connecting them to the
>>>> frontends via the ioctl mentioned above).
>>> Sounds logical. And that's why Kaffeine search for frontend/demux/dvr > 0 and 
>>> uses demux1 with frontend1. (That was just a guess since i've never seen 
>>> neither any such devices nor comments/recommendations/rules about such case).
>>> However, all dual tuners devices drivers i know expose the 2 frontends as 
>>> frontend0 in separate adapters. But all these devices seems to be USB.
>>> The fact that Kaffeine works with the experimental hvr4000 driver indicates 
>>> that this driver populates frontend1/demux1/dvr1 and then doesn't follow the 
>>> way you describe (since the tuners can't be used at once).
>>> I would like to hear from Steve on this point.
>> Correct, frontend1, demux1, dvr1 etc. All on the same adapter. The 
>> driver and multi-frontend patches manage exclusive access to the single 
>> internal resource.
> then please explain what is about the analog usage, which can always be
> first and don't tell it has to stay back, since you always sit on that
> bridge and else come nowhere ...

Hermann, I'm not sure I understand your question, but I'll try.

This has nothing to do with analog, I never suggested these patches 
effected analog.

Either you're confused, or I am :)

The multifrontend patches are related to DVB only, the analog ports on 
the cx88 remain untouched, unchanged.

- Steve

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