Allow setting bandwidth for R820T

This improves SDR performence for nearby channel interference.
As a sideeffect also improves dynamic range becase ADC is not overloaded
by onwanted singlas.

Signed-off-by: Steve Markgraf <steve@steve-m.de>

include/tuner_r82xx.h

@@ -115,5 +115,6 @@ int r82xx_standby(struct r82xx_priv *priv);
 int r82xx_init(struct r82xx_priv *priv);
 int r82xx_set_freq(struct r82xx_priv *priv, uint32_t freq);
 int r82xx_set_gain(struct r82xx_priv *priv, int set_manual_gain, int gain);
+int r82xx_set_bandwidth(struct r82xx_priv *priv, int bandwidth,  uint32_t rate);
 
 #endif

src/librtlsdr.c

@@ -126,6 +126,7 @@ struct rtlsdr_dev {
 };
 
 void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val);
+static int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq);
 
 /* generic tuner interface functions, shall be moved to the tuner implementations */
 int e4000_init(void *dev) {
@@ -238,7 +239,20 @@ int r820t_set_freq(void *dev, uint32_t freq) {
 	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
 	return r82xx_set_freq(&devt->r82xx_p, freq);
 }
-int r820t_set_bw(void *dev, int bw) { return 0; }
+
+int r820t_set_bw(void *dev, int bw) {
+	int r;
+	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
+
+	r = r82xx_set_bandwidth(&devt->r82xx_p, bw, devt->rate);
+	if(r < 0)
+		return r;
+	r = rtlsdr_set_if_freq(devt, r);
+	if (r)
+		return r;
+	return rtlsdr_set_center_freq(devt, devt->freq);
+}
+
 int r820t_set_gain(void *dev, int gain) {
 	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
 	return r82xx_set_gain(&devt->r82xx_p, 1, gain);
@@ -670,7 +684,7 @@ int rtlsdr_deinit_baseband(rtlsdr_dev_t *dev)
 	return r;
 }
 
-int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq)
+static int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq)
 {
 	uint32_t rtl_xtal;
 	int32_t if_freq;

src/tuner_r82xx.c

@@ -1073,6 +1073,82 @@ int r82xx_set_gain(struct r82xx_priv *priv, int set_manual_gain, int gain)
 	return 0;
 }
 
+/* Bandwidth contribution by low-pass filter. */
+static const int r82xx_if_low_pass_bw_table[] = {
+	1700000, 1600000, 1550000, 1450000, 1200000, 900000, 700000, 550000, 450000, 350000
+};
+
+#define FILT_HP_BW1 350000
+#define FILT_HP_BW2 380000
+int r82xx_set_bandwidth(struct r82xx_priv *priv, int bw, uint32_t rate)
+{
+	int rc;
+	unsigned int i;
+	int real_bw = 0;
+	uint8_t reg_0a;
+	uint8_t reg_0b;
+
+	if (bw > 7000000) {
+		// BW: 8 MHz
+		reg_0a = 0x10;
+		reg_0b = 0x0b;
+		priv->int_freq = 4570000;
+	} else if (bw > 6000000) {
+		// BW: 7 MHz
+		reg_0a = 0x10;
+		reg_0b = 0x2a;
+		priv->int_freq = 4570000;
+	} else if (bw > r82xx_if_low_pass_bw_table[0] + FILT_HP_BW1 + FILT_HP_BW2) {
+		// BW: 6 MHz
+		reg_0a = 0x10;
+		reg_0b = 0x6b;
+		priv->int_freq = 3570000;
+	} else {
+		reg_0a = 0x00;
+		reg_0b = 0x80;
+		priv->int_freq = 2300000;
+
+		if (bw > r82xx_if_low_pass_bw_table[0] + FILT_HP_BW1) {
+			bw -= FILT_HP_BW2;
+			priv->int_freq += FILT_HP_BW2;
+			real_bw += FILT_HP_BW2;
+		} else {
+			reg_0b |= 0x20;
+		}
+
+		if (bw > r82xx_if_low_pass_bw_table[0]) {
+			bw -= FILT_HP_BW1;
+			priv->int_freq += FILT_HP_BW1;
+			real_bw += FILT_HP_BW1;
+		} else {
+			reg_0b |= 0x40;
+		}
+
+		// find low-pass filter
+		for(i = 0; i < ARRAY_SIZE(r82xx_if_low_pass_bw_table); ++i) {
+			if (bw > r82xx_if_low_pass_bw_table[i])
+				break;
+		}
+		--i;
+		reg_0b |= 15 - i;
+		real_bw += r82xx_if_low_pass_bw_table[i];
+
+		priv->int_freq -= real_bw / 2;
+	}
+
+	rc = r82xx_write_reg_mask(priv, 0x0a, reg_0a, 0x10);
+	if (rc < 0)
+		return rc;
+
+	rc = r82xx_write_reg_mask(priv, 0x0b, reg_0b, 0xef);
+	if (rc < 0)
+		return rc;
+
+	return priv->int_freq;
+}
+#undef FILT_HP_BW1
+#undef FILT_HP_BW2
+
 int r82xx_set_freq(struct r82xx_priv *priv, uint32_t freq)
 {
 	int rc = -1;