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[media] dib8000: estimate strength in dBm

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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: Mauro Carvalho Chehab <m.chehab@samsung.com>
Acked-by: Patrick Boettcher <pboettcher@kernellabs.com>
This commit is contained in:
Mauro Carvalho Chehab 2013-12-16 20:00:34 -03:00
parent 6ef06e78c7
commit b4600d70c0
1 changed files with 21 additions and 2 deletions
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23
drivers/media/dvb-frontends/dib8000.c
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@ -11,6 +11,7 @@
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/mutex.h>
#include <asm/div64.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_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->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 dtv_frontend_properties *c = &state->fe[0]->dtv_property_cache;
int i, lock;
u64 tmp;
u32 snr, val;
u16 strength;
/* Get Signal 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 */
if (!time_after(jiffies, state->get_stats_time))