lsm303d/l3gd20: change filters to 50Hz analog on-chip filters

after discussion with Leonard these analog on-chip filters should be
at 50Hz

src/drivers/l3gd20/l3gd20.cpp

@@ -93,10 +93,15 @@ static const int ERROR = -1;
 /* keep lowpass low to avoid noise issues */
 #define RATE_95HZ_LP_25HZ		((0<<7) | (0<<6) | (0<<5) | (1<<4))
 #define RATE_190HZ_LP_25HZ		((0<<7) | (1<<6) | (0<<5) | (1<<4))
+#define RATE_190HZ_LP_50HZ		((0<<7) | (1<<6) | (1<<5) | (0<<4))
 #define RATE_190HZ_LP_70HZ		((0<<7) | (1<<6) | (1<<5) | (1<<4))
 #define RATE_380HZ_LP_20HZ		((1<<7) | (0<<6) | (1<<5) | (0<<4))
+#define RATE_380HZ_LP_25HZ		((1<<7) | (0<<6) | (0<<5) | (1<<4))
+#define RATE_380HZ_LP_50HZ		((1<<7) | (0<<6) | (1<<5) | (0<<4))
 #define RATE_380HZ_LP_100HZ		((1<<7) | (0<<6) | (1<<5) | (1<<4))
 #define RATE_760HZ_LP_30HZ		((1<<7) | (1<<6) | (0<<5) | (0<<4))
+#define RATE_760HZ_LP_35HZ		((1<<7) | (1<<6) | (0<<5) | (1<<4))
+#define RATE_760HZ_LP_50HZ		((1<<7) | (1<<6) | (1<<5) | (0<<4))
 #define RATE_760HZ_LP_100HZ		((1<<7) | (1<<6) | (1<<5) | (1<<4))
 
 #define ADDR_CTRL_REG2			0x21
@@ -662,15 +667,15 @@ L3GD20::set_samplerate(unsigned frequency)
 
 	} else if (frequency <= 200) {
 		_current_rate = 190;
-		bits |= RATE_190HZ_LP_70HZ;
+		bits |= RATE_190HZ_LP_50HZ;
 
 	} else if (frequency <= 400) {
 		_current_rate = 380;
-		bits |= RATE_380HZ_LP_100HZ;
+		bits |= RATE_380HZ_LP_50HZ;
 
 	} else if (frequency <= 800) {
 		_current_rate = 760;
-		bits |= RATE_760HZ_LP_100HZ;
+		bits |= RATE_760HZ_LP_50HZ;
 	} else {
 		return -EINVAL;
 	}

src/drivers/lsm303d/lsm303d.cpp

@@ -599,7 +599,12 @@ LSM303D::reset()
 	accel_set_range(LSM303D_ACCEL_DEFAULT_RANGE_G);
 	accel_set_samplerate(LSM303D_ACCEL_DEFAULT_RATE);
 	accel_set_driver_lowpass_filter((float)LSM303D_ACCEL_DEFAULT_RATE, (float)LSM303D_ACCEL_DEFAULT_DRIVER_FILTER_FREQ);
-	accel_set_onchip_lowpass_filter_bandwidth(0); // this gives 773Hz
+
+	// we setup the anti-alias on-chip filter as 50Hz. We believe
+	// this operates in the analog domain, and is critical for
+	// anti-aliasing. The 2 pole software filter is designed to
+	// operate in conjunction with this on-chip filter
+	accel_set_onchip_lowpass_filter_bandwidth(LSM303D_ACCEL_DEFAULT_ONCHIP_FILTER_FREQ);
 
 	mag_set_range(LSM303D_MAG_DEFAULT_RANGE_GA);
 	mag_set_samplerate(LSM303D_MAG_DEFAULT_RATE);