[linux-dvb] Re: diseqc in DVB/apps/szap/szap.c

[Oliver Endriss <o.endriss@gmx.de>]

Andreas Oberritter wrote:
> On Wed, 2003-04-23 at 22:20, Franck Arnaud wrote:
> > In function diseqc of DVB/apps/szap/szap.c we have:
> >
> >  (sat_no / 4) % 2 ? SEC_MINI_B : SEC_MINI_A);

This does not make much sense (if you want to implement something like 
Figure 3 in section 5.3 of the spec).

> > if sat_no is the satellite number we always get the same result for
> > the typical 1-4. I think the "/ 4" should not be there:
> >
> >  sat_no % 2 ? SEC_MINI_B : SEC_MINI_A);

Ack.

> > (this should have no impact on modern diseqc switches which I think
> > listen to proper commands rather than this, but I have a dumb one.)

Ack.

> The upper one may be valid if you have up to 8 single diseqc lnbs
> connected to a 8/1 diseqc switch. but i think szap wouldn't work then
> anyway because it does not repeat diseqc messages.
>
> The lower one seems more typical, e.g. having one toneburst switch to
> switch between two quattro lnbs.

Typically, none of them will work in a *cascaded* setup because the 
second switch needs up to 100ms for initialization (according to the 
spec).

> OT:
> I wonder why the diseqc specification says, that toneburst has to be
> sent after the diseqc message. Think of having one toneburst A/B
> switch, two Diseqc 4/1 switches and eight diseqc lnbs.

I think you misunderstood the spec. Section 5.3 defines how DiSEqC and 
backward compatible signals can be *combined* to perform the same task 
without having to worry whether the switch understands
- Mini DiSEqC (aka tone burst) or
- Full DiSEqC
This section does *not* address cascaded setups which will typically 
need two or more messages.

> If one would like to switch from lnb 0 to lnb 4, then the diseqc
> message will reach switch A and toneburst will then switch from A
> (range 0..3) to B (range 4..7), so lnb 4 will never hear the message,
> which is bad, because:
> 1.) the diseqc switch B does then not know which input should be
> used. 2.) the diseqc lnbs rely on these message to change
> polarization and band.

In this case you have to use something like
	<ToneBurst>  <100ms delay>  <Full DiSEqC msg>
The spec doesn't forbid this.

Oliver


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