[linux-dvb] Re: V4 API Implementation Q's

[Rob.McConnell@Zarlink.Com]

                      Johannes                                                                                                   
                      Stezenbach               To:       linux-dvb@linuxtv.org                                                   
                      <js@convergence.d        cc:                                                                               
                      e>                       Subject:  [linux-dvb] Re: V4 API Implementation Q's                               
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                      12-Apr-2004 09:58                                                                                          
                      PM                                                                                                         
                                                                                                                                 
                                                                                                                                 











Hi Johannes,

> On Tue, Apr 06, 2004 at 07:27:24PM +0100, Rob.McConnell@Zarlink.Com
wrote:
> > Michael Hunold wrote:
> > > If you have a hardware that mixes all these kind of filters to one
> > > device, you'll have a hard time to calculate how many filters are
> > > actually available of each kind.
> >
> > OK, from our discussions it sounds like it will be the responsibility
of
> > the code "underneath" the API to control the resources.  We just
specify
> > the max number of *h/w* filters of each type - right?  e.g. If you
don't
> > have dedicated record h/w then you should set the
> > DVB_DMX_CAP_NUM_RECORDING_FILTERS to 0 - correct?

> Yes and no.

> IMHO recording filters are such a basic feature that they
> should be emulated in software if there is no special
> purpose hardware for them (see av7110). Unless you write
> a driver for a simple STB which won't support recording at all.

Yes I agree.

> However, the V3 API allows one to allocate+set a filter now, and
> start the filter later. I don't know how useful this is. I left
> this out in V4 because the software I know does not actually make
> use of it, it always sets filters with DMX_IMMEDIATE_START.

> It sounds useful to make the distinction between filter allocation
> and filter setting in the API. But how would this actually improve
> applications?

OK, personally I don't know how useful this is either, but there is a lot
of STB s/w out there at the moment that makes the distinction between:

1. allocating a filter/feed.
2. setting up the filter/feed spec.
3. "hitting" the go button.

This API isn't Zarlink specific but if you ever deal with a few well known
UK STB design houses you will see that this is how they operate -
strangely. ;^)  So, really I/we could do with finding out if there is a
real technical reason for performing these steps independently (rather than
in one go). So if there is anyone out there with a plausible reason, they
please feel free to contribute.

Thanks,

Rob : )




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