[linux-dvb] ATSC card with 2 RF inputs.

Todd Ignasiak ignasiak at gmail.com
Sat Jul 16 18:31:20 CEST 2005


On 7/16/05, Patrick Boettcher <patrick.boettcher at desy.de> wrote:
> Hi,
> 
> On Fri, 15 Jul 2005, Mac Michaels wrote:
> >> This is what came into my mind: (very schematic)
> >>
> >> in the lgdt3302-driver there will be a
> >>
> >> int lgdt3302_set_rf_input(*fe, index)
> >> {
> >>      /* set the correct rf_input-path */
> >> }
> >> EXPORT_SYMBOL(lgdt3302_set_rf_input);
> >>
> >> add a pll_set-callback to the dt3302_config. This
> >> callback is called in set_frontend.
> >>
> >> if (state->config->pll_set)
> >>      state->config->pll_set(fe,fep);
> >>
> >> in cx88-dvb.c you set the pll_set-callback for the Gold-Q
> >> card to a function which could look like this:
> >>
> >> int cx88_gold_q_pll_set(*fe,frontend_parameters)
> >> {
> >>      /* do the stuff, eg. set pll1 for 8VSB and/or pll2 for
> >> QAM or so */
> >>
> >>      lgdt3302_set_rf_input(fe,appropriate_rf_input);
> >> }
> >
> > Thank you Patrick, your suggestion makes sense. How does the
> > application learn about the multiple RF input capability?
> 
> This is a good questions. To avoid the API extension it could be enough to
> program the correct PLL against the modulation-type:
> 
> 1) in the pll_set-callback for the Gold Q card:
> 
> if (modulation == QAM64 || modulation == QAM256) {
>         set_pll1_marked_with_cable();
>         lgdt3302_set_rf_input(fe,0);
> } else {
>         set_pll2_marked_with_ant();
>         lgdt3302_set_rf_input(fe,1);
> }
> 
> I'm not sure if that is obvious enough to the user. He/she would need to
> stick to the labels of the connectors when connecting the source.

This would work for my current configuration, and is certainly better
than not having access to one input.   Although, I could see it
causing confusion when a user didn't realize the implied behavior.

A scenario where this would be a limitation, actually one I ran into
with the Fusion windows software, is where a user wants to have two
inputs of the same type.   This is probably rare with cable inputs,
but is fairly common with antenna inputs.  In my area, I have two
broadcast locations in different directions.  So, with my other HD
card (MyHD MDP-120) I hooked antennas to both RF inputs, and my
channels would be distributed between both inputs.


> > Is an additional FE_CAN_SEL_RF needed? Would this be added
> > to the documention for the DVB API somewhere.

Aren't there DVB-T cards that have two RF inputs?   I'm surprised this
hasn't been seen before.

> 2) That would be difficult to handle. You would need to extend all
> DVB/ATSC applications adding an option to choose the RF-input.
> 
> 3) I heard, that the V3 API does not support multiple frontends per
> device, otherwise this would have been an option, too. (The frontend is
> registered twice, one time for the ANT-Input-PLL and a second time for the
> CABLE-Input-PLL)
> 
> I'm for 1). ;)
> 
> Patrick.
> 
> --
>    Mail: patrick.boettcher at desy.de
>    WWW:  http://www.wi-bw.tfh-wildau.de/~pboettch/
> 
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