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

Andreas Oberritter obi at linuxtv.org
Thu Sep 11 00:59:31 CEST 2008

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).


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