[linux-dvb] [RFC] associating pcr with vcxo

Andreas Oberritter obi at linuxtv.org
Tue Jul 26 14:05:51 CEST 2005


Hi Johannes,

On Tue, 2005-07-26 at 11:23 +0200, Johannes Stezenbach wrote:
> Andreas Oberritter wrote:
> > if you have multiple displays and/or Picture-In-Picture decoding, then
> > you have to define one PCR per display as master for vcxo control.
> > 
> > Therefore I propose the following simple interface:
> > 
> > struct dmx_stc_mapping {
> > 	unsigned int clock_num;
> > 	unsigned int pcr_num;
> > }
> > 
> > #define DMX_SET_STC_MAPPING _IOWR('o', 51, struct dmx_stc_mapping)
> 
> I think the naming is a bit misleading, because in your first
> sentence you say that this is about setting the "master for
> vcxo control". I.e. (if I get it right) you have one 27MHz
> crystal, but two PCR/STC. Obviously the vcxo can be synced to
> only one of them, so you have to choose (for PiP usually the
> one with the bigger picture).
> 
> How about:
> 
> struct dmx_vcxo_control {
> 	unsigned int vcxo_num;	// in case you have more than one vcxo
>  	unsigned int pcr_num;	// which PCR to sync the vcxo to
> };
> 
> #define DMX_VCXO_CONTROL _IOWR('o', 51, struct dmx_vcxo_control)
> 
> or maybe DMX_SET_VCXO_SYNC_SOURCE?

You are right, "stc" was quite confusing.

I've been told that using a VCXO is not the only way to synchronize the
transmitter and receiver clock, so how about your proposal with "vcxo"
replaced by the more generic "clock"?

Regards,
Andreas





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