Re: [PATCH] tda18271-fe: Fix dvb-c standard selection

2013-11-02 Thread Mauro Carvalho Chehab 
Em Sat, 02 Nov 2013 23:05:14 +0200
CrazyCat crazyca...@narod.ru escreveu:

 Fix dvb-c standard selection - qam8 for ANNEX_AC
 
 Signed-off-by: Evgeny Plehov evgenyple...@ukr.net
 diff --git a/drivers/media/tuners/tda18271-fe.c 
 b/drivers/media/tuners/tda18271-fe.c
 index 4995b89..6a385c8 100644
 --- a/drivers/media/tuners/tda18271-fe.c
 +++ b/drivers/media/tuners/tda18271-fe.c
 @@ -960,16 +960,12 @@ static int tda18271_set_params(struct dvb_frontend *fe)
   break;
   case SYS_DVBC_ANNEX_B:
   bw = 600;
 - /* falltrough */
 + map = std_map-qam_6;
 + break;
   case SYS_DVBC_ANNEX_A:
   case SYS_DVBC_ANNEX_C:
 - if (bw = 600) {
 - map = std_map-qam_6;
 - } else if (bw = 700) {
 - map = std_map-qam_7;
 - } else {
 - map = std_map-qam_8;
 - }
 + bw = 800;
 + map = std_map-qam_8;

This is wrong, as it breaks for 6MHz-spaced channels, like what's used
in Brazil and Japan.

What happens here is that, if the tuner uses a too wide lowpass filter,
the interference will be higher at the demod, and it may not be able
to decode.

As the bandwidth is already estimated by the DVB frontend core, the
tuners should be adjusted to get the closest filter for a given
bandwidth.

So, the driver is correct (and it is tested under 6MHz spaced channels).

   break;
   default:
   tda_warn(modulation type not supported!\n);
 
 --
 To unsubscribe from this list: send the line unsubscribe linux-media in
 the body of a message to majord...@vger.kernel.org
 More majordomo info at  http://vger.kernel.org/majordomo-info.html


-- 

Cheers,
Mauro
--
To unsubscribe from this list: send the line unsubscribe linux-media in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] tda18271-fe: Fix dvb-c standard selection

2013-11-02 Thread Mauro Carvalho Chehab 
Em Sat, 02 Nov 2013 23:31:58 +0200
CrazyCat crazyca...@narod.ru escreveu:

 Mauro Carvalho Chehab пишет:
  This is wrong, as it breaks for 6MHz-spaced channels, like what's used
  in Brazil and Japan.
 
  What happens here is that, if the tuner uses a too wide lowpass filter,
  the interference will be higher at the demod, and it may not be able
  to decode.
 
  As the bandwidth is already estimated by the DVB frontend core, the
  tuners should be adjusted to get the closest filter for a given
  bandwidth.
 
  So, the driver is correct (and it is tested under 6MHz spaced channels).
 
 But usual applications only set cable standard (Annex A/C or B) and not set 
 bandwidth. So for annex A/C default selected 6MHz ?

Usual applications set the symbol rate, and symbol rate is easily
converted into bandwidth. The DVB core does that. see 
dtv_set_frontend():

switch (c-delivery_system) {
case SYS_ATSC:
case SYS_DVBC_ANNEX_B:
c-bandwidth_hz = 600;
break;
case SYS_DVBC_ANNEX_A:
rolloff = 115;
break;
case SYS_DVBC_ANNEX_C:
rolloff = 113;
break;
default:
break;
}
if (rolloff)
c-bandwidth_hz = (c-symbol_rate * rolloff) / 100;

-- 

Cheers,
Mauro
--
To unsubscribe from this list: send the line unsubscribe linux-media in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html