Re: [linux-dvb] [PATCH] cx24116 DVB-S modulation fix

From: Steven Toth <stoth@linuxtv.org>
To: Christophe Thommeret <hftom@free.fr>
Cc: linux-dvb@linuxtv.org
Subject: Re: [linux-dvb] [PATCH] cx24116 DVB-S modulation fix
Date: Tue, 14 Oct 2008 11:10:14 -0400	[thread overview]
Message-ID: <48F4B656.6010404@linuxtv.org> (raw)
In-Reply-To: <200810141451.02941.hftom@free.fr>

Christophe Thommeret wrote:
> Le Tuesday 14 October 2008 12:29:49 Darron Broad, vous avez écrit :
>> In message <200810141133.36559.hftom@free.fr>, Christophe Thommeret wrote:
>>
>> hi
>>
>>> Hi,
>>>
>>> This patch makes cx24116 to behave like other dvb-s frontends.
>> Unlike most DVB-S cards the those with a cx24116 use S2API
>> this makes them somewhat different.
>>
>>> This is needed especially because QAM_AUTO is used in a lot of scan files.
>> What scan files are you referring to? The
>> cx24116 only does PSK, not AM. QAM_AUTO
>> doesn't sound right. the cx24116 can't
>> auto detect anything, but that's another
>> story...
> 
> dvbscan initial tuning data files for DVB-S don't have an entry for 
> modulation. So an app like kaffeine simply set modulation to QAM_AUTO.
> Why not QPSK, you ask? Simply because DVB-S standard allows QPSK and 16QAM. 
> Maybe there is not a single 16QAM TP all over the world, but it's still a 
> valid modulation for DVB-S.
> So, we set modulation to QAM_AUTO when it's unknown/unspecified, like in 
> dvbscan files (those being also used by kaffeine). And it works pretty well, 
> just because most dvb-s can only do QPSK and so force modulation to QPSK 
> instead of returning a notsup.
> See this as software QAM_AUTO :)

I've only glanced briefly at the patch but setting the modulation type 
to QAM_AUTO, and expecting the card to support it I think is a bad idea.

I can accept the argument that the current driver will not accept 16QAM, 
but that's not the problem being discussed. (I'll address this in a 
separate patch)

Call DTV_CLEAR should also default your rolloff to 3.5.

Let's investigate a better approach.

kaffeine should be working well already, with the current code. Unless 
it was recently broken - in which case please discuss.

- Steve

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