[mythtv] diseqc

Allan Stirling Dibblahmythml0015 at pendor.org
Wed May 24 20:26:52 UTC 2006


Daniel Kristjansson wrote:
> On Wed, 2006-05-24 at 15:33 -0400, Yeasah Pell wrote:
>> The DVB DiSEqC code in myth has some shortcomings that make it difficult 
>> to use for my hardware. I'd like to have a quick discussion about what's 
>> wrong with it, and the best way to improve the state of things.
> <snip>
>> I have already done some of this work, but I'd like some feedback as to 
>> whether this is perceived as being generally useful, and if so, whether 
>> this seems like a good approach.
Glad to see someone else looking at this!

> 
> Both the DiSEqC code and the CAM code are a mess.
> 
This I completely agree with.

Unfortunately, DiSEqC isn't as easy as it first appears.

Most of the 'cheap' devices on the market are simple 
switches - These may be either simple tone-switches or true 
DiSEqC devices. It is not possible to reliably chain similar 
devices in any way, since the first device in the chain will 
be switched, THEN will possibly pass the next command 
(assuming it's a duplicate) through to it's downstream 
devices. 100ms pauses are recommended in the specifications 
between switching operations, etc.

DiSEqC 2.0 specifies a 'back-channel' which does allow 
feedback of status. The bus master (DVB card) has to poll 
the positioner for this. However... It's optional in the spec.


Cheers,

Allan.


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