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EKF: Minimise data buffer lengths

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Saves RAM and reduces output predictor errors by using the smallest data buffer length that meets time delay and update rate requirements.
This commit is contained in:
Paul Riseborough
2016-11-07 09:06:45 +11:00
parent 750a8874c1
commit d5b398ddb1
3 changed files with 35 additions and 2 deletions
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EKF/estimator_interface.h
+15 -2
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@@ -273,8 +273,21 @@ protected:
parameters _params; // filter parameters
static const uint8_t OBS_BUFFER_LENGTH = 10; // defines how many measurement samples we can buffer
static const uint8_t IMU_BUFFER_LENGTH = 30; // defines how many imu samples we can buffer
/*
OBS_BUFFER_LENGTH defines how many observations (non-IMU measurements) we can buffer
which sets the maximum frequency at which we can process non-IMU measurements. Measurements that
arrive too soon after the previous measurement will not be processed.
max freq (Hz) = (OBS_BUFFER_LENGTH - 1) / (IMU_BUFFER_LENGTH * FILTER_UPDATE_PERIOD_MS * 0.001)
This can be adjusted to match the max sensor data rate plus some margin for jitter.
*/
uint8_t OBS_BUFFER_LENGTH;
/*
IMU_BUFFER_LENGTH defines how many IMU samples we buffer which sets the time delay from current time to the
EKF fusion time horizon and therefore the maximum sensor time offset relative to the IMU that we can compensate for.
max sensor time offet (msec) = IMU_BUFFER_LENGTH * FILTER_UPDATE_PERIOD_MS
This can be adjusted to a value that is FILTER_UPDATE_PERIOD_MS longer than the maximum observation time delay.
*/
uint8_t IMU_BUFFER_LENGTH;
static const unsigned FILTER_UPDATE_PERIOD_MS = 10; // ekf prediction period in milliseconds
unsigned _min_obs_interval_us; // minimum time interval between observations that will guarantee data is not lost (usec)