ardupilot/libraries/AP_NavEKF2/AP_NavEKF2_Buffer.h

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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
// EKF Buffer models
// this buffer model is to be used for observation buffers,
// the data is pushed into buffer like any standard ring buffer
// return is based on the sample time provided
template <typename element_type>
class obs_ring_buffer_t
{
public:
struct element_t{
element_type element;
} *buffer;
// initialise buffer, returns false when allocation has failed
bool init(uint32_t size)
{
buffer = new element_t[size];
if(buffer == NULL)
{
return false;
}
memset(buffer,0,size*sizeof(element_t));
_size = size;
_head = 0;
_tail = 0;
_new_data = false;
return true;
}
/*
* Searches through a ring buffer and return the newest data that is older than the
* time specified by sample_time_ms
* Zeros old data so it cannot not be used again
* Returns false if no data can be found that is less than 100msec old
*/
bool recall(element_type &element,uint32_t sample_time)
{
if(!_new_data) {
return false;
}
bool success = false;
uint8_t tail = _tail, bestIndex;
if(_head == tail) {
if (buffer[tail].element.time_ms != 0 && buffer[tail].element.time_ms <= sample_time) {
// if head is equal to tail just check if the data is unused and within time horizon window
if (((sample_time - buffer[tail].element.time_ms) < 100)) {
bestIndex = tail;
success = true;
_new_data = false;
}
}
} else {
while(_head != tail) {
// find a measurement older than the fusion time horizon that we haven't checked before
if (buffer[tail].element.time_ms != 0 && buffer[tail].element.time_ms <= sample_time) {
// Find the most recent non-stale measurement that meets the time horizon criteria
if (((sample_time - buffer[tail].element.time_ms) < 100)) {
bestIndex = tail;
success = true;
}
} else if(buffer[tail].element.time_ms > sample_time){
break;
}
tail = (tail+1)%_size;
}
}
if (success) {
element = buffer[bestIndex].element;
_tail = (bestIndex+1)%_size;
//make time zero to stop using it again,
//resolves corner case of reusing the element when head == tail
buffer[bestIndex].element.time_ms = 0;
return true;
} else {
return false;
}
}
/*
* Writes data and timestamp to a Ring buffer and advances indices that
* define the location of the newest and oldest data
*/
inline void push(element_type element)
{
// Advance head to next available index
_head = (_head+1)%_size;
// New data is written at the head
buffer[_head].element = element;
_new_data = true;
}
// writes the same data to all elements in the ring buffer
inline void reset_history(element_type element, uint32_t sample_time) {
for (uint8_t index=0; index<_size; index++) {
buffer[index].element = element;
}
}
// zeroes all data in the ring buffer
inline void reset() {
_head = 0;
_tail = 0;
_new_data = false;
memset(buffer,0,_size*sizeof(element_t));
}
private:
uint8_t _size,_head,_tail,_new_data;
};
// Folowing buffer model is for IMU data,
// it achieves a distance of sample size
// between youngest and oldest
template <typename element_type>
class imu_ring_buffer_t
{
public:
struct element_t{
element_type element;
} *buffer;
// initialise buffer, returns false when allocation has failed
bool init(uint32_t size)
{
buffer = new element_t[size];
if(buffer == NULL)
{
return false;
}
memset(buffer,0,size*sizeof(element_t));
_size = size;
_youngest = 0;
_oldest = 0;
return true;
}
/*
* Writes data to a Ring buffer and advances indices that
* define the location of the newest and oldest data
*/
inline void push_youngest_element(element_type element)
{
// push youngest to the buffer
_youngest = (_youngest+1)%_size;
buffer[_youngest].element = element;
// set oldest data index
_oldest = (_youngest+1)%_size;
}
// retrieve the oldest data from the ring buffer tail
inline element_type pop_oldest_element() {
element_type ret = buffer[_oldest].element;
return ret;
}
// writes the same data to all elements in the ring buffer
inline void reset_history(element_type element) {
for (uint8_t index=0; index<_size; index++) {
buffer[index].element = element;
}
}
// zeroes all data in the ring buffer
inline void reset() {
_youngest = 0;
_oldest = 0;
memset(buffer,0,_size*sizeof(element_t));
}
// retrieves data from the ring buffer at a specified index
inline element_type& operator[](uint32_t index) {
return buffer[index].element;
}
// returns the index for the ring buffer oldest data
inline uint8_t get_oldest_index(){
return _oldest;
}
// returns the index for the ring buffer youngest data
inline uint8_t get_youngest_index(){
return _youngest;
}
private:
uint8_t _size,_oldest,_youngest;
};