ardupilot/ArduCopter/ekf_check.pde

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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/**
*
* ekf_check.pde - detects failures of the ekf or inertial nav system
* triggers an alert to the pilot and helps take countermeasures
*
*/
#ifndef EKF_CHECK_ITERATIONS_MAX
# define EKF_CHECK_ITERATIONS_MAX 10 // 1 second (ie. 10 iterations at 10hz) of bad variances signals a failure
#endif
#ifndef EKF_CHECK_WARNING_TIME
# define EKF_CHECK_WARNING_TIME (30*1000) // warning text messages are sent to ground no more than every 30 seconds
#endif
// Enumerator for types of check
enum EKFCheckType {
CHECK_NONE = 0,
CHECK_DCM = 1,
CHECK_EKF = 2
};
////////////////////////////////////////////////////////////////////////////////
// EKF_check strucutre
////////////////////////////////////////////////////////////////////////////////
static struct {
uint8_t fail_count_compass; // number of iterations ekf or dcm have been out of tolerances
uint8_t bad_compass : 1; // true if dcm or ekf should be considered untrusted (fail_count_compass has exceeded EKF_CHECK_ITERATIONS_MAX)
uint32_t last_warn_time; // system time of last warning in milliseconds. Used to throttle text warnings sent to GCS
} ekf_check_state;
// ekf_dcm_check - detects if ekf variances or dcm yaw errors that are out of tolerance and triggers failsafe
// should be called at 10hz
void ekf_dcm_check()
{
EKFCheckType check_type = CHECK_NONE;
// decide if we should check ekf or dcm
if (ahrs.have_inertial_nav() && g.ekfcheck_thresh > 0.0f) {
check_type = CHECK_EKF;
} else if (g.dcmcheck_thresh > 0.0f) {
check_type = CHECK_DCM;
}
// return immediately if motors are not armed, ekf check is disabled, not using ekf or usb is connected
if (!motors.armed() || ap.usb_connected || check_type == CHECK_NONE) {
ekf_check_state.fail_count_compass = 0;
ekf_check_state.bad_compass = false;
AP_Notify::flags.ekf_bad = ekf_check_state.bad_compass;
failsafe_ekf_off_event(); // clear failsafe
return;
}
// compare compass and velocity variance vs threshold
if ((check_type == CHECK_EKF && ekf_over_threshold()) || (check_type == CHECK_DCM && dcm_over_threshold())) {
// if compass is not yet flagged as bad
if (!ekf_check_state.bad_compass) {
// increase counter
ekf_check_state.fail_count_compass++;
// if counter above max then trigger failsafe
if (ekf_check_state.fail_count_compass >= EKF_CHECK_ITERATIONS_MAX) {
// limit count from climbing too high
ekf_check_state.fail_count_compass = EKF_CHECK_ITERATIONS_MAX;
ekf_check_state.bad_compass = true;
// log an error in the dataflash
Log_Write_Error(ERROR_SUBSYSTEM_EKFINAV_CHECK, ERROR_CODE_EKFINAV_CHECK_BAD_VARIANCE);
// send message to gcs
if ((hal.scheduler->millis() - ekf_check_state.last_warn_time) > EKF_CHECK_WARNING_TIME) {
if (check_type == CHECK_EKF) {
gcs_send_text_P(SEVERITY_HIGH,PSTR("EKF variance"));
} else {
gcs_send_text_P(SEVERITY_HIGH,PSTR("DCM bad heading"));
}
ekf_check_state.last_warn_time = hal.scheduler->millis();
}
failsafe_ekf_event();
}
}
} else {
// reduce counter
if (ekf_check_state.fail_count_compass > 0) {
ekf_check_state.fail_count_compass--;
// if compass is flagged as bad and the counter reaches zero then clear flag
if (ekf_check_state.bad_compass && ekf_check_state.fail_count_compass == 0) {
ekf_check_state.bad_compass = false;
// log recovery in the dataflash
Log_Write_Error(ERROR_SUBSYSTEM_EKFINAV_CHECK, ERROR_CODE_EKFINAV_CHECK_VARIANCE_CLEARED);
// clear failsafe
failsafe_ekf_off_event();
}
}
}
// set AP_Notify flags
AP_Notify::flags.ekf_bad = ekf_check_state.bad_compass;
// To-Do: add ekf variances to extended status
}
// dcm_over_threshold - returns true if the dcm yaw error is over the tolerance
static bool dcm_over_threshold()
{
// return true if yaw error is over the threshold
return (g.dcmcheck_thresh > 0.0f && ahrs.get_error_yaw() > g.dcmcheck_thresh);
}
// ekf_over_threshold - returns true if the ekf's variance are over the tolerance
static bool ekf_over_threshold()
{
#if AP_AHRS_NAVEKF_AVAILABLE
// return false immediately if disabled
if (g.ekfcheck_thresh <= 0.0f) {
return false;
}
// use EKF to get variance
float posVar, hgtVar, tasVar;
Vector3f magVar;
Vector2f offset;
float compass_variance;
float vel_variance;
ahrs.get_NavEKF().getVariances(vel_variance, posVar, hgtVar, magVar, tasVar, offset);
compass_variance = magVar.length();
// return true if compass and velocity variance over the threshold
return (compass_variance >= g.ekfcheck_thresh && vel_variance >= g.ekfcheck_thresh);
#else
return false;
#endif
}
// failsafe_ekf_event - perform ekf failsafe
static void failsafe_ekf_event()
{
// return immediately if ekf failsafe already triggered
if (failsafe.ekf) {
return;
}
// do nothing if motors disarmed or not in flight mode that requires GPS
if (!motors.armed() || !mode_requires_GPS(control_mode)) {
return;
}
// EKF failsafe event has occurred
failsafe.ekf = true;
Log_Write_Error(ERROR_SUBSYSTEM_FAILSAFE_EKFINAV, ERROR_CODE_FAILSAFE_OCCURRED);
// take action based on flight mode
if (mode_requires_GPS(control_mode)) {
set_mode_land_with_pause();
}
// if flight mode is LAND ensure it's not the GPS controlled LAND
if (control_mode == LAND) {
land_do_not_use_GPS();
}
}
// failsafe_ekf_off_event - actions to take when EKF failsafe is cleared
static void failsafe_ekf_off_event(void)
{
// return immediately if not in ekf failsafe
if (!failsafe.ekf) {
return;
}
// clear flag and log recovery
failsafe.ekf = false;
Log_Write_Error(ERROR_SUBSYSTEM_FAILSAFE_EKFINAV, ERROR_CODE_FAILSAFE_RESOLVED);
}