[mythtv] diseqc

[Yeasah Pell]

>DiSEqC 2.0 supports bidirectional commands, and the spec defines 
>everything you'd need to know what the motor is doing. Unfortunately I 
>don't know of any motor that supports this, and even if they existed, 
>the linux dvb api doesn't support 2.0 (although many cards do.) However, 
>for my setup I have the diseqc class calculate how long it will take to 
>do the move based on the last known location, and the motor manufacturer 
>specifications for the angular speed at 13V and 18V. It works fairly 
>well, though it's obviously not as good as having real motor feedback.
>  
>
This reminds me -- back when I was first doing the angular rate 
calculations I encountered a problem where the EIT scanner seemed to use 
a diseqc object with a different angular position than the actual last 
position that the recorder used. I forgot all about this, but now that I 
think about it I wonder if this is a bug that is responsible for the 
occasional lost recording I get, under this kind of scenario:

[recorder runs at position 1, finishes]
[active eit scanner begins at position 1, motor moves to 1 -- doesn't 
realize it was already at 1]
[active eit scanner moves to position 2, motor moves to 2]
[recorder runs at position 1, but the recorder's diseqc object still 
reflects position 1, so it doesn't move]

This was on 19-fixes, I haven't tried to see if it's a problem in one of 
the more recent branches, or even if it's still a problem in 19-fixes. 
I'll check it out when I get a chance.