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

Manu Abraham abraham.manu at gmail.com
Wed Feb 15 13:00:55 CET 2006


Johannes Stezenbach wrote:
> 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?
>   

Yes..
> 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.
>   

Yeah, it looks good.


Manu





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