[linux-dvb] DVB-T devices supporting hierarchical mode?

Johannes Stezenbach js at linuxtv.org
Wed Feb 15 12:56:12 CET 2006


On Wed, Feb 15, 2006, Patrick Boettcher wrote:
> On Tue, 14 Feb 2006, Mauro Borghi wrote:
> >Do you know about LinuxDVB-supported devices which are known to support 
> >hierarchical modulation?
> >Is it meant to be sufficient setting HIERARCHY_2 in the struct passed to 
> >the frontend device when tuning, in order to select the LOW priority 
> >stream?
> 
> Although it was most likely never tested with most of the demod-drivers in 
> linux-dvb it should be possible with all of them.
> 
> >From the tests I did with a Twinhan 7045 USB2 clone (from digicom), the 
> >device seems to always lock on the HIGH priority stream, no matter what 
> >params are passed!
> 
> The Twinhan box has a MT352 inside and the controlling is done inside the 
> FX2 USB firmware. As hierarchical transmission has significant drawbacks 
> when used and no one (not even Twinhan :) ) expected that to be used 
> anywhere, they don't have it implemented. Ie. there is no way to give this 
> information to the firmware.

It seems to me that a parameter is missing in the Linux DVB API
to select between the high/low priority stream. If I understand
it correctly the hierarchy mode just modifies the modulation scheme,
and you still need a seperate knob to select which TS (high or low)
the frontend should output. Can someone confirm this?

I so, an easy way to fix without breaking API binary compatibility
would be:

typedef enum fe_hierarchy {
        HIERARCHY_NONE,
        HIERARCHY_1,
        HIERARCHY_2,
        HIERARCHY_4,
        HIERARCHY_AUTO
        HIERARCHY_1_LP = HIERARCHY_1 | 0x100,
        HIERARCHY_2_LP,
        HIERARCHY_4_LP,
        HIERARCHY_AUTO_LP
} fe_hierarchy_t;

And of course frontend drivers would need to be fixed to handle this.


Johannes



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