AP_InertialSensor: keep a queue of gyro samples for use by the rate thread

decimate the gyro window locally
configure rate loop buffer based on AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
allow backends to be updated from rate thread
output debug error if rate loop buffer overruns
add support for updating filter parameters independently of propagating samples
add rate loop config abstraction that allows code to be elided on non-copter builds
must be using harmonic notch to use rate thread
mediate fast rate loop buffer using mutex and binary semaphore
ensure gyro samples are used when the rate loop buffer isn't

Co-Authored-By: Andrew Tridgell <andrew@tridgell.net>

libraries/AP_InertialSensor/AP_InertialSensor.h

@@ -9,6 +9,8 @@
 #define AP_INERTIAL_SENSOR_ACCEL_VIBE_FILT_HZ           2.0f    // accel vibration filter hz
 #define AP_INERTIAL_SENSOR_ACCEL_PEAK_DETECT_TIMEOUT_MS 500     // peak-hold detector timeout
 
+#define AP_INERTIAL_SENSOR_RATE_LOOP_BUFFER_SIZE 8     // gyro buffer size for rate loop
+
 #include <AP_HAL/AP_HAL_Boards.h>
 
 #include <stdint.h>
@@ -34,6 +36,7 @@
 class AP_InertialSensor_Backend;
 class AuxiliaryBus;
 class AP_AHRS;
+class FastRateBuffer;
 
 /*
   forward declare AP_Logger class. We can't include logger.h
@@ -51,6 +54,7 @@ class AP_Logger;
 class AP_InertialSensor : AP_AccelCal_Client
 {
     friend class AP_InertialSensor_Backend;
+    friend class FastRateBuffer;
 
 public:
     AP_InertialSensor();
@@ -161,12 +165,12 @@ public:
     const Vector3f& get_gyro_for_fft(void) const { return _gyro_for_fft[_first_usable_gyro]; }
     FloatBuffer&  get_raw_gyro_window(uint8_t instance, uint8_t axis) { return _gyro_window[instance][axis]; }
     FloatBuffer&  get_raw_gyro_window(uint8_t axis) { return get_raw_gyro_window(_first_usable_gyro, axis); }
-    uint16_t get_raw_gyro_rate_hz() const { return get_raw_gyro_rate_hz(_first_usable_gyro); }
-    uint16_t get_raw_gyro_rate_hz(uint8_t instance) const { return _gyro_raw_sample_rates[_first_usable_gyro]; }
 #if AP_INERTIALSENSOR_HARMONICNOTCH_ENABLED
     bool has_fft_notch() const;
 #endif
 #endif
+    uint16_t get_raw_gyro_rate_hz(uint8_t instance) const { return _gyro_raw_sample_rates[_first_usable_gyro]; }
+    uint16_t get_raw_gyro_rate_hz() const { return get_raw_gyro_rate_hz(_first_usable_gyro); }
     bool set_gyro_window_size(uint16_t size);
     // get accel offsets in m/s/s
     const Vector3f &get_accel_offsets(uint8_t i) const { return _accel_offset(i); }
@@ -263,6 +267,7 @@ public:
     AuxiliaryBus *get_auxiliary_bus(int16_t backend_id, uint8_t instance);
 
     void detect_backends(void);
+    void update_backends();
 
     // accel peak hold detector
     void set_accel_peak_hold(uint8_t instance, const Vector3f &accel);
@@ -798,6 +803,30 @@ private:
     bool raw_logging_option_set(RAW_LOGGING_OPTION option) const {
         return (raw_logging_options.get() & int32_t(option)) != 0;
     }
+    // if AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+    // Support for the fast rate thread in copter
+    FastRateBuffer* fast_rate_buffer;
+
+public:
+    // enable the fast rate buffer and start pushing samples to it
+    void enable_fast_rate_buffer();
+    // disable the fast rate buffer and stop pushing samples to it
+    void disable_fast_rate_buffer();
+    // get the next available gyro sample from the fast rate buffer
+    bool get_next_gyro_sample(Vector3f& gyro);
+    // get the number of available gyro samples in the fast rate buffer
+    uint32_t get_num_gyro_samples();
+    // set the rate at which samples are collected, unused samples are dropped
+    void set_rate_decimation(uint8_t rdec);
+    // are gyro samples being sourced from the rate loop buffer
+    bool use_rate_loop_gyro_samples() const;
+    // push a new gyro sample into the fast rate buffer
+    bool push_next_gyro_sample(const Vector3f& gyro);
+    // run the filter parmeter update code.
+    void update_backend_filters();
+    // are rate loop samples enabled for this instance?
+    bool is_rate_loop_gyro_enabled(uint8_t instance) const;
+    // endif AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
 };
 
 namespace AP {

libraries/AP_InertialSensor/AP_InertialSensor_Backend.cpp

@@ -2,6 +2,7 @@
 
 #include <AP_HAL/AP_HAL.h>
 #include <AP_AHRS/AP_AHRS.h>
+#include "AP_InertialSensor_rate_config.h"
 #include "AP_InertialSensor.h"
 #include "AP_InertialSensor_Backend.h"
 #include <AP_Logger/AP_Logger.h>
@@ -254,9 +255,21 @@ void AP_InertialSensor_Backend::apply_gyro_filters(const uint8_t instance, const
             notch.filter[instance].reset();
         }
 #endif
+        gyro_filtered = _imu._gyro_filtered[instance];
+    }
+
+#if AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+    if (_imu.is_rate_loop_gyro_enabled(instance)) {
+        if (_imu.push_next_gyro_sample(gyro_filtered)) {
+            // if we used the value, record it for publication to the front-end
+            _imu._gyro_filtered[instance] = gyro_filtered;
+        }
     } else {
         _imu._gyro_filtered[instance] = gyro_filtered;
     }
+#else
+    _imu._gyro_filtered[instance] = gyro_filtered;
+#endif
 }
 
 void AP_InertialSensor_Backend::_notify_new_gyro_raw_sample(uint8_t instance,
@@ -772,6 +785,7 @@ void AP_InertialSensor_Backend::update_gyro(uint8_t instance) /* front end */
     if (has_been_killed(instance)) {
         return;
     }
+
     if (_imu._new_gyro_data[instance]) {
         _publish_gyro(instance, _imu._gyro_filtered[instance]);
 #if HAL_GYROFFT_ENABLED

libraries/AP_InertialSensor/AP_InertialSensor_Backend.h

@@ -53,6 +53,15 @@ public:
      */
     virtual bool update() = 0; /* front end */
 
+    // if AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+    /*
+     * Update the filter parameters. Called by the frontend to propagate
+     * filter parameters to the frontend structure via the
+     * update_gyro_filters() and update_accel_filters() functions
+     */
+    void update_filters() __RAMFUNC__; /* front end */
+    // endif AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+
     /*
      * optional function to accumulate more samples. This is needed for drivers that don't use a timer to gather samples
      */

libraries/AP_InertialSensor/AP_InertialSensor_rate_config.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <AP_Vehicle/AP_Vehicle_Type.h>
+#include <AP_HAL/AP_HAL_Boards.h>
+#include <AP_InertialSensor/AP_InertialSensor_config.h>
+
+#ifndef AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+#define AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED (AP_INERTIALSENSOR_ENABLED && HAL_INS_RATE_LOOP && AP_INERTIALSENSOR_HARMONICNOTCH_ENABLED && APM_BUILD_TYPE(APM_BUILD_ArduCopter))
+#endif

libraries/AP_InertialSensor/FastRateBuffer.cpp

@@ -0,0 +1,124 @@
+/*
+   This program 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.
+
+   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <AP_AHRS/AP_AHRS.h>
+#include "AP_InertialSensor_rate_config.h"
+#include "AP_InertialSensor.h"
+#include "AP_InertialSensor_Backend.h"
+
+#if AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+#include "FastRateBuffer.h"
+#include <stdio.h>
+
+extern const AP_HAL::HAL& hal;
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS
+// hal.console can be accessed from bus threads on ChibiOS
+#define debug(fmt, args ...)  do {hal.console->printf("IMU: " fmt "\n", ## args); } while(0)
+#else
+#define debug(fmt, args ...)  do {printf("IMU: " fmt "\n", ## args); } while(0)
+#endif
+
+void AP_InertialSensor::enable_fast_rate_buffer()
+{
+    fast_rate_buffer = NEW_NOTHROW FastRateBuffer();
+}
+
+void AP_InertialSensor::disable_fast_rate_buffer()
+{
+    delete fast_rate_buffer;
+    fast_rate_buffer = nullptr;
+}
+
+uint32_t AP_InertialSensor::get_num_gyro_samples()
+{
+    return fast_rate_buffer->get_num_gyro_samples();
+}
+
+void AP_InertialSensor::set_rate_decimation(uint8_t rdec)
+{
+    fast_rate_buffer->set_rate_decimation(rdec);
+}
+
+// are gyro samples being sourced from the rate loop buffer
+bool AP_InertialSensor::use_rate_loop_gyro_samples() const
+{
+    return fast_rate_buffer != nullptr;
+}
+
+// whether or not to push the current gyro sample
+bool AP_InertialSensor::is_rate_loop_gyro_enabled(uint8_t instance) const
+{
+    return use_rate_loop_gyro_samples() && fast_rate_buffer->use_rate_loop_gyro_samples() && instance == AP::ahrs().get_primary_gyro_index();
+}
+
+bool AP_InertialSensor::get_next_gyro_sample(Vector3f& gyro)
+{
+    if (!use_rate_loop_gyro_samples()) {
+        return false;
+    }
+
+    return fast_rate_buffer->get_next_gyro_sample(gyro);
+}
+
+bool FastRateBuffer::get_next_gyro_sample(Vector3f& gyro)
+{
+    if (!use_rate_loop_gyro_samples()) {
+        return false;
+    }
+
+    if (_rate_loop_gyro_window.available() == 0) {
+        _notifier.wait_blocking();
+    }
+
+    WITH_SEMAPHORE(_mutex);
+
+    return _rate_loop_gyro_window.pop(gyro);
+}
+
+bool AP_InertialSensor::push_next_gyro_sample(const Vector3f& gyro)
+{
+    if (++fast_rate_buffer->rate_decimation_count < fast_rate_buffer->rate_decimation) {
+        return false;
+    }
+    /*
+        tell the rate thread we have a new sample
+    */
+    WITH_SEMAPHORE(fast_rate_buffer->_mutex);
+
+    if (!fast_rate_buffer->_rate_loop_gyro_window.push(gyro)) {
+        debug("dropped rate loop sample");
+    }
+    fast_rate_buffer->rate_decimation_count = 0;
+    fast_rate_buffer->_notifier.signal();
+    return true;
+}
+
+void AP_InertialSensor::update_backend_filters()
+{
+    for (uint8_t i=0; i<_backend_count; i++) {
+        _backends[i]->update_filters();
+    }
+}
+
+void AP_InertialSensor_Backend::update_filters()
+{
+    WITH_SEMAPHORE(_sem);
+
+    update_accel_filters(accel_instance);
+    update_gyro_filters(gyro_instance);
+}
+
+#endif // AP_INERTIALSENSOR_RATE_LOOP_WINDOW_ENABLED

libraries/AP_InertialSensor/FastRateBuffer.h

@@ -0,0 +1,50 @@
+/*
+   This program 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.
+
+   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#pragma once
+
+#include "AP_InertialSensor.h"
+
+#if AP_INERTIALSENSOR_FAST_SAMPLE_WINDOW_ENABLED
+
+#define AP_INERTIAL_SENSOR_RATE_LOOP_BUFFER_SIZE 8     // gyro buffer size for rate loop
+
+#include <AP_HAL/AP_HAL_Boards.h>
+#include <AP_HAL/utility/RingBuffer.h>
+#include <AP_Math/AP_Math.h>
+#include <AP_HAL/Semaphores.h>
+
+class FastRateBuffer
+{
+    friend class AP_InertialSensor;
+public:
+    bool get_next_gyro_sample(Vector3f& gyro);
+    uint32_t get_num_gyro_samples() { return _rate_loop_gyro_window.available(); }
+    void set_rate_decimation(uint8_t rdec) { rate_decimation = rdec; }
+    // whether or not to push the current gyro sample
+    bool use_rate_loop_gyro_samples() const { return rate_decimation > 0; }
+    bool gyro_samples_available() { return  _rate_loop_gyro_window.available() > 0; }
+
+private:
+    /*
+      binary semaphore for rate loop to use to start a rate loop when
+      we hav finished filtering the primary IMU
+     */
+    ObjectBuffer<Vector3f> _rate_loop_gyro_window{AP_INERTIAL_SENSOR_RATE_LOOP_BUFFER_SIZE};
+    uint8_t rate_decimation; // 0 means off
+    uint8_t rate_decimation_count;
+    HAL_BinarySemaphore _notifier;
+    HAL_Semaphore _mutex;
+};
+#endif