or51211: Changed SNR and signal strength calculations

From: Rusty Scott <rustys@ieee.org>

Removes embedded log functions and makes use of the DVB math functions to
provide SNR in dB.  The changes are modeled after recent changes made to
the LGDT330x frontends in lgdt330x.c

Signed-off-by: Rusty Scott <rustys@ieee.org>
Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>

1 files changed, 50 insertions, 74 deletions

diff --git a/linux/drivers/media/dvb/frontends/or51211.c b/linux/drivers/media/dvb/frontends/or51211.c
index 2bf124b53..048d7cfe1 100644
--- a/linux/drivers/media/dvb/frontends/or51211.c
+++ b/linux/drivers/media/dvb/frontends/or51211.c
@@ -39,6 +39,7 @@
 #include <linux/slab.h>
 #include <asm/byteorder.h>
 
+#include "dvb_math.h"
 #include "dvb_frontend.h"
 #include "or51211.h"
 
@@ -63,6 +64,7 @@ struct or51211_state {
 
 	/* Demodulator private data */
 	u8 initialized:1;
+	u32 snr; /* Result of last SNR claculation */
 
 	/* Tuner private data */
 	u32 current_frequency;
@@ -292,107 +294,81 @@ static int or51211_read_status(struct dvb_frontend* fe, fe_status_t* status)
 	return 0;
 }
 
-/* log10-1 table at .5 increments from 1 to 100.5 */
-static unsigned int i100x20log10[] = {
-		0,  352,  602,  795,  954, 1088, 1204, 1306, 1397, 1480,
-	 1556, 1625, 1690, 1750, 1806, 1858, 1908, 1955, 2000, 2042,
-	 2082, 2121, 2158, 2193, 2227, 2260, 2292, 2322, 2352, 2380,
-	 2408, 2434, 2460, 2486, 2510, 2534, 2557, 2580, 2602, 2623,
-	 2644, 2664, 2684, 2704, 2723, 2742, 2760, 2778, 2795, 2813,
-	 2829, 2846, 2862, 2878, 2894, 2909, 2924, 2939, 2954, 2968,
-	 2982, 2996, 3010, 3023, 3037, 3050, 3062, 3075, 3088, 3100,
-	 3112, 3124, 3136, 3148, 3159, 3170, 3182, 3193, 3204, 3214,
-	 3225, 3236, 3246, 3256, 3266, 3276, 3286, 3296, 3306, 3316,
-	 3325, 3334, 3344, 3353, 3362, 3371, 3380, 3389, 3397, 3406,
-	 3415, 3423, 3432, 3440, 3448, 3456, 3464, 3472, 3480, 3488,
-	 3496, 3504, 3511, 3519, 3526, 3534, 3541, 3549, 3556, 3563,
-	 3570, 3577, 3584, 3591, 3598, 3605, 3612, 3619, 3625, 3632,
-	 3639, 3645, 3652, 3658, 3665, 3671, 3677, 3683, 3690, 3696,
-	 3702, 3708, 3714, 3720, 3726, 3732, 3738, 3744, 3750, 3755,
-	 3761, 3767, 3772, 3778, 3784, 3789, 3795, 3800, 3806, 3811,
-	 3816, 3822, 3827, 3832, 3838, 3843, 3848, 3853, 3858, 3863,
-	 3868, 3874, 3879, 3884, 3888, 3893, 3898, 3903, 3908, 3913,
-	 3918, 3922, 3927, 3932, 3936, 3941, 3946, 3950, 3955, 3960,
-	 3964, 3969, 3973, 3978, 3982, 3986, 3991, 3995, 4000, 4004,
-};
-
-static unsigned int denom[] = {1,1,100,1000,10000,100000,1000000,10000000,100000000};
+/* Calculate SNR estimation (scaled by 2^24)
 
-static unsigned int i20Log10(unsigned short val)
-{
-	unsigned int rntval = 100;
-	unsigned int tmp = val;
-	unsigned int exp = 1;
+   8-VSB SNR equation from Oren datasheets
 
-	while(tmp > 100) {tmp /= 100; exp++;}
+   For 8-VSB:
+     SNR[dB] = 10 * log10(219037.9454 / MSE^2 )
 
-	val = (2 * val)/denom[exp];
-	if (exp > 1) rntval = 2000*exp;
+   We re-write the snr equation as:
+     SNR * 2^24 = 10*(c - 2*intlog10(MSE))
+   Where for 8-VSB, c = log10(219037.9454) * 2^24 */
 
-	rntval += i100x20log10[val];
-	return rntval;
+static u32 calculate_snr(u32 mse, u32 c)
+{
+	if (mse == 0) /* No signal */
+		return 0;
+
+	mse = 2*intlog10(mse);
+	if (mse > c) {
+		/* 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 */
+		return 0;
+	}
+	return 10*(c - mse);
 }
 
-static int or51211_read_signal_strength(struct dvb_frontend* fe, u16* strength)
+static int or51211_read_snr(struct dvb_frontend* fe, u16* snr)
 {
 	struct or51211_state* state = fe->demodulator_priv;
 	u8 rec_buf[2];
-	u8 snd_buf[4];
-	u8 snr_equ;
-	u32 signal_strength;
+	u8 snd_buf[3];
 
 	/* SNR after Equalizer */
 	snd_buf[0] = 0x04;
 	snd_buf[1] = 0x00;
 	snd_buf[2] = 0x04;
-	snd_buf[3] = 0x00;
 
 	if (i2c_writebytes(state,state->config->demod_address,snd_buf,3)) {
-		printk(KERN_WARNING "or51211: read_status write error\n");
+		printk(KERN_WARNING "%s: error writing snr reg\n",
+		       __FUNCTION__);
 		return -1;
 	}
-	msleep(3);
 	if (i2c_readbytes(state,state->config->demod_address,rec_buf,2)) {
-		printk(KERN_WARNING "or51211: read_status read error\n");
+		printk(KERN_WARNING "%s: read_status read error\n",
+		       __FUNCTION__);
 		return -1;
 	}
-	snr_equ = rec_buf[0] & 0xff;
 
-	/* The value reported back from the frontend will be FFFF=100% 0000=0% */
-	signal_strength = (((5334 - i20Log10(snr_equ))/3+5)*65535)/1000;
-	if (signal_strength > 0xffff)
-		*strength = 0xffff;
-	else
-		*strength = signal_strength;
-	dprintk("read_signal_strength %i\n",*strength);
+	state->snr = calculate_snr(rec_buf[0], 89599047);
+	*snr = (state->snr) >> 16;
+
+	dprintk("%s: noise = 0x%02x, snr = %d.%02d dB\n", __FUNCTION__, rec_buf[0],
+		state->snr >> 24, (((state->snr>>8) & 0xffff) * 100) >> 16);
 
 	return 0;
 }
 
-static int or51211_read_snr(struct dvb_frontend* fe, u16* snr)
+static int or51211_read_signal_strength(struct dvb_frontend* fe, u16* strength)
 {
-	struct or51211_state* state = fe->demodulator_priv;
-	u8 rec_buf[2];
-	u8 snd_buf[4];
-
-	/* SNR after Equalizer */
-	snd_buf[0] = 0x04;
-	snd_buf[1] = 0x00;
-	snd_buf[2] = 0x04;
-	snd_buf[3] = 0x00;
-
-	if (i2c_writebytes(state,state->config->demod_address,snd_buf,3)) {
-		printk(KERN_WARNING "or51211: read_status write error\n");
-		return -1;
-	}
-	msleep(3);
-	if (i2c_readbytes(state,state->config->demod_address,rec_buf,2)) {
-		printk(KERN_WARNING "or51211: read_status read error\n");
-		return -1;
-	}
-	*snr = rec_buf[0] & 0xff;
-
-	dprintk("read_snr %i\n",*snr);
+	/* Calculate Strength from SNR up to 35dB */
+	/* Even though the SNR can go higher than 35dB, there is some comfort */
+	/* factor in having a range of strong signals that can show at 100%   */
+	struct or51211_state* state = (struct or51211_state*)fe->demodulator_priv;
+	u16 snr;
+	int ret;
+
+	ret = fe->ops.read_snr(fe, &snr);
+	if (ret != 0)
+		return ret;
+	/* Rather than use the 8.8 value snr, use state->snr which is 8.24 */
+	/* scale the range 0 - 35*2^24 into 0 - 65535 */
+	if (state->snr >= 8960 * 0x10000)
+		*strength = 0xffff;
+	else
+		*strength = state->snr / 8960;
 
 	return 0;
 }