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authorMauro Carvalho Chehab <m.chehab@samsung.com>2013-12-16 20:00:34 -0300
committerMauro Carvalho Chehab <m.chehab@samsung.com>2013-12-19 08:17:45 -0200
commitb4600d70c0927a9f61b26093c0f01db69f607a6f (patch)
treea0443f2b68a8b33d99170747ab02828e1882be0a /drivers/media/dvb-frontends/dib8000.c
parent6ef06e78c74cc4b2f45ea2e9adbe6d52cd246a6b (diff)
[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: Mauro Carvalho Chehab <m.chehab@samsung.com> Acked-by: Patrick Boettcher <pboettcher@kernellabs.com>
Diffstat (limited to 'drivers/media/dvb-frontends/dib8000.c')
-rw-r--r--drivers/media/dvb-frontends/dib8000.c23
1 files changed, 21 insertions, 2 deletions
diff --git a/drivers/media/dvb-frontends/dib8000.c b/drivers/media/dvb-frontends/dib8000.c
index 2dbf89365a97..faf469d1d437 100644
--- a/drivers/media/dvb-frontends/dib8000.c
+++ b/drivers/media/dvb-frontends/dib8000.c
@@ -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))