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Commit d12b791e authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
Browse files

[media] cxd2841er: adjust the dB scale for DVB-C 



Instead of using a relative frequency range, calibrate it to
show the results in dB. The callibration was done getting
samples with a signal generated from -50dBm to -12dBm,
incremented in steps of 0.5 dB, using 3 frequencies:
175 MHz, 410 MHz and 800 MHz. The modulated signal was
using QAM64, and it was used a linear interpolation of all
the results.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 988bd281

drivers/media/dvb-frontends/cxd2841er.c

+7 −2
Original line number Diff line number Diff line
@@ -1768,8 +1768,13 @@ static void cxd2841er_read_signal_strength(struct dvb_frontend *fe) 
	case SYS_DVBC_ANNEX_A:

		strength = cxd2841er_read_agc_gain_t_t2(priv,

							p->delivery_system);

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

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

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

		/*

		 * Formula was empirically determinated via linear regression,

		 * using frequencies: 175 MHz, 410 MHz and 800 MHz, and a

		 * stream modulated with QAM64

		 */

		p->strength.stat[0].uvalue = ((s32)strength) * 4045 / 1000 - 85224;

		break;

	case SYS_ISDBT:

		strength = 65535 - cxd2841er_read_agc_gain_i(