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Commit b4600d70 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
Browse files

[media] dib8000: estimate strength in dBm 



Better to have Signal strength in dB.
This takes a very rough estimation for the signal strength,
that was calibrated using a Dektec DTA-2111 Gold RF generator
and a Pixelview dib8076 stick.

It estimates the signal strength using a linear equation where:
	- the max is -22.5 dBm, with returns 55953
	- the min is -35.0 dBm, with returns 50110

With -22dBm, the signal strengh is returned as 65535.
Unfortunately, the min strength generated with DTA-2111 is
-35dBm.

It should be noticed that approximating it by a linear equation
is not right. I should probably be splitting it into 0.5 dB
linear segments, in order to get a higher precision, just like
it is done on mb86a20s, but that would force me to add some
attenuators, in order to get dB levels below -35dBm, which is,
btw, strong enough to get signal lock.

Signed-off-by: default avatarMauro Carvalho Chehab <m.chehab@samsung.com>
Acked-by: default avatarPatrick Boettcher <pboettcher@kernellabs.com>
parent 6ef06e78

drivers/media/dvb-frontends/dib8000.c

+21 −2
Original line number Original line Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/slab.h>

#include <linux/slab.h>

#include <linux/i2c.h>

#include <linux/i2c.h>

#include <linux/mutex.h>

#include <linux/mutex.h>

#include <asm/div64.h>





#include "dvb_math.h"

#include "dvb_math.h"
@@ -1002,7 +1003,7 @@ static void dib8000_reset_stats(struct dvb_frontend *fe) 
	c->post_bit_error.len = 1;

	c->post_bit_error.len = 1;

	c->post_bit_count.len = 1;

	c->post_bit_count.len = 1;





	c->strength.stat[0].scale = FE_SCALE_RELATIVE;

	c->strength.stat[0].scale = FE_SCALE_DECIBEL;

	c->strength.stat[0].uvalue = 0;

	c->strength.stat[0].uvalue = 0;





	c->cnr.stat[0].scale = FE_SCALE_NOT_AVAILABLE;

	c->cnr.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
@@ -3847,12 +3848,30 @@ static int dib8000_get_stats(struct dvb_frontend *fe, fe_status_t stat) 
	struct dib8000_state *state = fe->demodulator_priv;

	struct dib8000_state *state = fe->demodulator_priv;

	struct dtv_frontend_properties *c = &state->fe[0]->dtv_property_cache;

	struct dtv_frontend_properties *c = &state->fe[0]->dtv_property_cache;

	int i, lock;

	int i, lock;

	u64 tmp;

	u32 snr, val;

	u32 snr, val;

	u16 strength;

	u16 strength;





	/* Get Signal strength */

	/* Get Signal strength */

	dib8000_read_signal_strength(fe, &strength);

	dib8000_read_signal_strength(fe, &strength);

	c->strength.stat[0].uvalue = strength;



	/*

	 * Estimate it in dBm

	 * This calculus was empirically determinated by measuring the signal

	 * strength generated by a DTA-2111 RF generator directly connected into

	 * a dib8076 device. The real value can actually be different on other

	 * devices, depending if LNA is enabled or not, if diversity is enabled,

	 * etc.

	 */

	if (strength == 65535) {

		c->strength.stat[0].svalue = -22000;

	} else {

		tmp = strength * 25000L;

		do_div(tmp, 11646);

		c->strength.stat[0].svalue = tmp - 142569;

		if (c->strength.stat[0].svalue > -22000)

			c->strength.stat[0].svalue = -22000;

	}





	/* Check if 1 second was elapsed */

	/* Check if 1 second was elapsed */

	if (!time_after(jiffies, state->get_stats_time))

	if (!time_after(jiffies, state->get_stats_time))