Uses 4-th order low-pass for extracting gravity.
Most accelerometers have 8-bits accuracy so we beed to
reject 48dB in thestop-band, which requires a 4-th order
filter at the cut-off frequency we're using.
Change-Id: Ic00421d38d751641f86b1f3ad7663e6b44a91198
diff --git a/services/sensorservice/GravitySensor.cpp b/services/sensorservice/GravitySensor.cpp
index 18bd359..da72f9c 100644
--- a/services/sensorservice/GravitySensor.cpp
+++ b/services/sensorservice/GravitySensor.cpp
@@ -30,7 +30,7 @@
GravitySensor::GravitySensor(sensor_t const* list, size_t count)
: mSensorDevice(SensorDevice::getInstance()),
mEnabled(false), mAccTime(0),
- mLowPass(M_SQRT1_2, 1),
+ mLowPass(M_SQRT1_2, 1.5f),
mX(mLowPass), mY(mLowPass), mZ(mLowPass)
{
diff --git a/services/sensorservice/GravitySensor.h b/services/sensorservice/GravitySensor.h
index f9850b7..ff3bea7 100644
--- a/services/sensorservice/GravitySensor.h
+++ b/services/sensorservice/GravitySensor.h
@@ -37,7 +37,7 @@
double mAccTime;
SecondOrderLowPassFilter mLowPass;
- BiquadFilter mX, mY, mZ;
+ CascadedBiquadFilter mX, mY, mZ;
public:
GravitySensor(sensor_t const* list, size_t count);
diff --git a/services/sensorservice/SecondOrderLowPassFilter.cpp b/services/sensorservice/SecondOrderLowPassFilter.cpp
index e13e136..eeb6d1e 100644
--- a/services/sensorservice/SecondOrderLowPassFilter.cpp
+++ b/services/sensorservice/SecondOrderLowPassFilter.cpp
@@ -67,4 +67,23 @@
}
// ---------------------------------------------------------------------------
+
+CascadedBiquadFilter::CascadedBiquadFilter(const SecondOrderLowPassFilter& s)
+ : mA(s), mB(s)
+{
+}
+
+float CascadedBiquadFilter::init(float x)
+{
+ mA.init(x);
+ mB.init(x);
+ return x;
+}
+
+float CascadedBiquadFilter::operator()(float x)
+{
+ return mB(mA(x));
+}
+
+// ---------------------------------------------------------------------------
}; // namespace android
diff --git a/services/sensorservice/SecondOrderLowPassFilter.h b/services/sensorservice/SecondOrderLowPassFilter.h
index 998ca35..85698ca 100644
--- a/services/sensorservice/SecondOrderLowPassFilter.h
+++ b/services/sensorservice/SecondOrderLowPassFilter.h
@@ -54,6 +54,18 @@
float operator()(float in);
};
+/*
+ * Two cascaded biquad IIR filters
+ * (4-poles IIR)
+ */
+class CascadedBiquadFilter {
+ BiquadFilter mA;
+ BiquadFilter mB;
+public:
+ CascadedBiquadFilter(const SecondOrderLowPassFilter& s);
+ float init(float in);
+ float operator()(float in);
+};
// ---------------------------------------------------------------------------
}; // namespace android