Replace old lowpass with BiQuad for Vbat and Servo

Makefile

@@ -291,7 +291,6 @@ COMMON_SRC = build_config.c \
 		   flight/pid.c \
 		   flight/imu.c \
 		   flight/mixer.c \
-		   flight/lowpass.c \
 		   drivers/bus_i2c_soft.c \
 		   drivers/serial.c \
 		   drivers/sound_beeper.c \

src/main/config/config.c

@@ -334,7 +334,7 @@ void resetMixerConfig(mixerConfig_t *mixerConfig) {
     mixerConfig->yaw_jump_prevention_limit = 200;
 #ifdef USE_SERVOS
     mixerConfig->tri_unarmed_servo = 1;
-    mixerConfig->servo_lowpass_freq = 400;
+    mixerConfig->servo_lowpass_freq = 400.0f;
     mixerConfig->servo_lowpass_enable = 0;
 #endif
 }

src/main/flight/lowpass.c

@@ -1,118 +0,0 @@
-/*
- * This file is part of Cleanflight.
- *
- * Cleanflight is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Cleanflight is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include <stdbool.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <math.h>
-
-#include "common/maths.h"
-#include "flight/lowpass.h"
-
-//#define DEBUG_LOWPASS
-
-void generateLowpassCoeffs2(int16_t freq, lowpass_t *filter)
-{
-    float fixedScaler;
-    int i;
-
-    // generates coefficients for a 2nd-order butterworth low-pass filter
-    float freqf = (float)freq*0.001f;
-    float omega = tan_approx((float)M_PI*freqf/2.0f);
-    float scaling = 1.0f / (omega*omega + 1.4142136f*omega + 1.0f);
-
-
-#if defined(UNIT_TEST) && defined(DEBUG_LOWPASS)
-    printf("lowpass cutoff: %f, omega: %f\n", freqf, omega);
-#endif
-   
-    filter->bf[0] = scaling * omega*omega;
-    filter->bf[1] = 2.0f * filter->bf[0];
-    filter->bf[2] = filter->bf[0];
-
-    filter->af[0] = 1.0f;
-    filter->af[1] = scaling * (2.0f * omega*omega - 2.0f);
-    filter->af[2] = scaling * (omega*omega - 1.4142136f * omega + 1.0f);
-
-    // Scale for fixed-point
-    filter->input_bias = 1500; // Typical servo range is 1500 +/- 500
-    filter->input_shift = 16;
-    filter->coeff_shift = 24; 
-    fixedScaler = (float)(1ULL << filter->coeff_shift);
-    for (i = 0; i < LOWPASS_NUM_COEF; i++) {
-        filter->a[i] = LPF_ROUND(filter->af[i] * fixedScaler);
-        filter->b[i] = LPF_ROUND(filter->bf[i] * fixedScaler);
-#if defined(UNIT_TEST) && defined(DEBUG_LOWPASS)
-        printf("(%d) bf: %f af: %f b: %ld a: %ld\n", i, 
-                filter->bf[i], filter->af[i], filter->b[i], filter->a[i]);
-#endif
-    }
-
-    filter->freq = freq;
-}
-
-int32_t lowpassFixed(lowpass_t *filter, int32_t in, int16_t freq)
-{
-    int16_t coefIdx;
-    int64_t out;
-    int32_t in_s;
-  
-    // Check to see if cutoff frequency changed
-    if (freq != filter->freq) {
-        filter->init = false;
-    }
-
-    // Initialize if needed
-    if (!filter->init) {
-        generateLowpassCoeffs2(freq, filter);
-        for (coefIdx = 0; coefIdx < LOWPASS_NUM_COEF; coefIdx++) {
-            filter->x[coefIdx] = (in - filter->input_bias) << filter->input_shift;
-            filter->y[coefIdx] = (in - filter->input_bias) << filter->input_shift;
-        }
-        filter->init = true;
-    }
-
-    // Unbias input and scale
-    in_s = (in - filter->input_bias) << filter->input_shift;
-
-    // Delays
-    for (coefIdx = LOWPASS_NUM_COEF-1; coefIdx > 0; coefIdx--) {
-        filter->x[coefIdx] = filter->x[coefIdx-1];
-        filter->y[coefIdx] = filter->y[coefIdx-1];
-    }
-    filter->x[0] = in_s;
-
-    // Accumulate result
-    out = filter->x[0] * filter->b[0];
-    for (coefIdx = 1; coefIdx < LOWPASS_NUM_COEF; coefIdx++) {
-        out -= filter->y[coefIdx] * filter->a[coefIdx];
-        out += filter->x[coefIdx] * filter->b[coefIdx];
-    }
-
-    // Scale output by coefficient shift
-    out >>= filter->coeff_shift;
-    filter->y[0] = (int32_t)out;
-
-    // Scale output by input shift and round
-    out = (out + (1 << (filter->input_shift-1))) >> filter->input_shift;
-    
-    // Reapply bias
-    out += filter->input_bias;
-
-    return (int32_t)out;
-}
-

src/main/flight/lowpass.h

@@ -1,41 +0,0 @@
-/*
- * This file is part of Cleanflight.
- *
- * Cleanflight is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Cleanflight is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#pragma once
-
-
-#define LOWPASS_NUM_COEF 3
-#define LPF_ROUND(x) (x < 0 ? (x - 0.5f) : (x + 0.5f))
-
-typedef struct lowpass_s {
-    bool init;
-    int16_t freq;                           // Normalized freq in 1/1000ths
-    float bf[LOWPASS_NUM_COEF];
-    float af[LOWPASS_NUM_COEF];
-    int64_t b[LOWPASS_NUM_COEF];
-    int64_t a[LOWPASS_NUM_COEF];
-    int16_t coeff_shift;
-    int16_t input_shift;
-    int32_t input_bias;
-    float xf[LOWPASS_NUM_COEF];
-    float yf[LOWPASS_NUM_COEF];
-    int32_t x[LOWPASS_NUM_COEF];
-    int32_t y[LOWPASS_NUM_COEF];
-} lowpass_t;
-
-void generateLowpassCoeffs2(int16_t freq, lowpass_t *filter);
-int32_t lowpassFixed(lowpass_t *filter, int32_t in, int16_t freq);

src/main/flight/mixer.c

@@ -19,6 +19,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 
 #include "platform.h"
 #include "debug.h"
@@ -27,6 +28,7 @@
 
 #include "common/axis.h"
 #include "common/maths.h"
+#include "common/filter.h"
 
 #include "drivers/system.h"
 #include "drivers/pwm_output.h"
@@ -34,6 +36,7 @@
 #include "drivers/sensor.h"
 #include "drivers/accgyro.h"
 #include "drivers/system.h"
+#include "drivers/gyro_sync.h"
 
 #include "rx/rx.h"
 
@@ -48,7 +51,6 @@
 #include "flight/failsafe.h"
 #include "flight/pid.h"
 #include "flight/imu.h"
-#include "flight/lowpass.h"
 
 #include "config/runtime_config.h"
 #include "config/config.h"
@@ -77,7 +79,6 @@ int16_t servo[MAX_SUPPORTED_SERVOS];
 static int useServo;
 STATIC_UNIT_TESTED uint8_t servoCount;
 static servoParam_t *servoConf;
-static lowpass_t lowpassFilters[MAX_SUPPORTED_SERVOS];
 #endif
 
 static const motorMixer_t mixerQuadX[] = {
@@ -924,6 +925,8 @@ void filterServos(void)
 {
 #ifdef USE_SERVOS
     int16_t servoIdx;
+    static bool servoFilterIsSet;
+    biquad_t servoFitlerState[MAX_SUPPORTED_SERVOS];
 
 #if defined(MIXER_DEBUG)
     uint32_t startTime = micros();
@@ -931,7 +934,11 @@ void filterServos(void)
 
     if (mixerConfig->servo_lowpass_enable) {
         for (servoIdx = 0; servoIdx < MAX_SUPPORTED_SERVOS; servoIdx++) {
-            servo[servoIdx] = (int16_t)lowpassFixed(&lowpassFilters[servoIdx], servo[servoIdx], mixerConfig->servo_lowpass_freq);
+            if (!servoFilterIsSet) {
+                BiQuadNewLpf(mixerConfig->servo_lowpass_freq, &servoFitlerState[servoIdx], targetLooptime);
+                servoFilterIsSet = true;
+            }
+            servo[servoIdx] = lrintf(applyBiQuadFilter((float) servo[servoIdx], &servoFitlerState[servoIdx]));
 
             // Sanity check
             servo[servoIdx] = constrain(servo[servoIdx], servoConf[servoIdx].min, servoConf[servoIdx].max);

src/main/io/serial_cli.c

@@ -620,7 +620,7 @@ const clivalue_t valueTable[] = {
     { "yaw_jump_prevention_limit",  VAR_UINT16 | MASTER_VALUE, &masterConfig.mixerConfig.yaw_jump_prevention_limit, .config.minmax = { YAW_JUMP_PREVENTION_LIMIT_LOW,  YAW_JUMP_PREVENTION_LIMIT_HIGH } },
 #ifdef USE_SERVOS
     { "tri_unarmed_servo",          VAR_INT8   | MASTER_VALUE | MODE_LOOKUP, &masterConfig.mixerConfig.tri_unarmed_servo, .config.lookup = { TABLE_OFF_ON } },
-    { "servo_lowpass_freq",         VAR_INT16  | MASTER_VALUE, &masterConfig.mixerConfig.servo_lowpass_freq, .config.minmax = { 10,  400} },
+    { "servo_lowpass_freq",         VAR_FLOAT  | MASTER_VALUE, &masterConfig.mixerConfig.servo_lowpass_freq, .config.minmax = { 10,  400} },
     { "servo_lowpass_enable",       VAR_INT8   | MASTER_VALUE | MODE_LOOKUP, &masterConfig.mixerConfig.servo_lowpass_enable, .config.lookup = { TABLE_OFF_ON } },
 #endif
 

src/main/sensors/battery.c

@@ -17,10 +17,12 @@
 
 #include "stdbool.h"
 #include "stdint.h"
+#include <math.h>
 
 #include "platform.h"
 
 #include "common/maths.h"
+#include "common/filter.h"
 
 #include "drivers/adc.h"
 #include "drivers/system.h"
@@ -33,7 +35,6 @@
 #include "rx/rx.h"
 
 #include "io/rc_controls.h"
-#include "flight/lowpass.h"
 #include "io/beeper.h"
 
 #define VBATT_PRESENT_THRESHOLD_MV    10
@@ -54,7 +55,6 @@ int32_t mAhDrawn = 0;               // milliampere hours drawn from the battery
 batteryConfig_t *batteryConfig;
 
 static batteryState_e batteryState;
-static lowpass_t lowpassFilter;
 
 uint16_t batteryAdcToVoltage(uint16_t src)
 {
@@ -66,12 +66,18 @@ uint16_t batteryAdcToVoltage(uint16_t src)
 static void updateBatteryVoltage(void)
 {
     uint16_t vbatSample;
-    uint16_t vbatFiltered;
+    biquad_t vbatFilterState;
+    static bool vbatFilterIsSet;
+
+    if (!vbatFilterIsSet) {
+        BiQuadNewLpf(0.5f, &vbatFilterState, 20000);
+        vbatFilterIsSet = true;
+    }
 
     // store the battery voltage with some other recent battery voltage readings
     vbatSample = vbatLatestADC = adcGetChannel(ADC_BATTERY);
-    vbatFiltered = (uint16_t)lowpassFixed(&lowpassFilter, vbatSample, VBATT_LPF_FREQ);
+    vbatSample = lrintf(applyBiQuadFilter((float) vbatSample, &vbatFilterState));
-    vbat = batteryAdcToVoltage(vbatFiltered);
+    vbat = batteryAdcToVoltage(vbatSample);
 }
 
 #define VBATTERY_STABLE_DELAY 40