[linux-dvb] [PATCH] lgdt330x: SNR and signal strength reporting

Patrick Boettcher patrick.boettcher at desy.de
Mon Oct 30 08:41:34 CET 2006


Hi,

On Sun, 29 Oct 2006, Michael Krufky wrote:
> I'm posting this to the list for final review before requesting merge into master.

You get what you've asked for:

> 
> lgdt330x: SNR and signal strength reporting
> 
> Update the SNR calculations to use the new dvb_math log function, and add
> SNR calculations for all supported modulations for both lg dt3302 and dt3303.
> The QAM equations don't appear in the dt3302 datasheet, so the ones from the
> dt3303 datasheet were used.
> 
> SNR returned is the actual value in dB as 8.8 fixed point.
> 
> Reporting of real signal strength isn't supported, so rather than return 0,
> which confuses some software and users, a re-scaled SNR value is returned.
> 
> Code originally by Rusty Scott.
> 
> Signed-off-by: Trent Piepho <xyzzy at speakeasy.org>
> Signed-off-by: Rusty Scott <rustys at ieee.org>
> Signed-off-by: Michael Krufky <mkrufky at linuxtv.org>
> 
> diff -r a80a23f896b2 -r 7d0f07be41e8 linux/drivers/media/dvb/frontends/lgdt330x.c
> --- a/linux/drivers/media/dvb/frontends/lgdt330x.c	Sun Oct 29 11:12:27 2006 -0300
> +++ b/linux/drivers/media/dvb/frontends/lgdt330x.c	Sun Oct 29 11:35:39 2006 -0500
> @@ -31,9 +31,6 @@
>   *   Air2PC/AirStar 2 ATSC 3rd generation (HD5000)
>   *   pcHDTV HD5500
>   *
> - * TODO:
> - * signal strength always returns 0.
> - *
>   */
>  
>  #include <linux/kernel.h>
> @@ -46,8 +43,12 @@
>  #include <asm/byteorder.h>
>  
>  #include "dvb_frontend.h"
> +#include "dvb_math.h"
>  #include "lgdt330x_priv.h"
>  #include "lgdt330x.h"
> +
> +/* Use Equalizer Mean Sqaured Error instead of Phaser Tracker MSE */
                         ^^^^^^^

Squared?

> +		/* Negative SNR, which is possible, but realisticly the
> +		demod will lose lock before the signal gets this bad.  The
> +		API only allows for unsigned values, so just return 0 */

In DVB-T QPSK FEC 1/2 it is possible to receive while having a negative 
SNR.

best regards,
Patrick.

--
  Mail: patrick.boettcher at desy.de
  WWW:  http://www.wi-bw.tfh-wildau.de/~pboettch/



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