common: Implement accelerometer calibration

This change implements the hybrid accelerometer calibration
algorithm described in
https://drive.google.com/corp/drive/u/0/folders/13k8AWvVkCg8KUr1HhD2qv6_ob1ixgCbE

1. Waits until the device is still
2. Adds a still sample to an orientation accumulator
   - If the new sample is close to an existing one, they're
   merged.
   - If the new sample is unique, it is added to the list of
   orientations in a FIFO manner (may be evicting an older
   sample).
   - Once enough orientations have been gathered, run the
   kasa algorithm.
   - The kasa algorithm should yield a radius that's near 1g,
   since all the samples were added when still. If this isn't
   the case, we fall back on newton's method (which takes
   longer).

BUG=b:138303429,chromium:1023858
BRANCH=None
TEST=buildall with new unit tests

Change-Id: I98bb0d365017d8a916b008c7c0c263345a9cddac
Signed-off-by: Yuval Peress <peress@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1879716
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>

1 files changed, 51 insertions, 0 deletions

diff --git a/include/accel_cal.h b/include/accel_cal.h
new file mode 100644
index 0000000000..cfba5b915d
--- /dev/null
+++ b/include/accel_cal.h
@@ -0,0 +1,51 @@
+/* Copyright 2020 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Online accelerometer calibration */
+
+#ifndef __CROS_EC_ACCEL_CAL_H
+#define __CROS_EC_ACCEL_CAL_H
+
+#include "kasa.h"
+#include "newton_fit.h"
+#include "stdbool.h"
+#include "stillness_detector.h"
+
+struct accel_cal_algo {
+	struct kasa_fit kasa_fit;
+	struct newton_fit newton_fit;
+};
+
+struct accel_cal {
+	struct still_det still_det;
+	struct accel_cal_algo *algos;
+	uint8_t num_temp_windows;
+	fpv3_t bias;
+};
+
+/**
+ * Reset the accelerometer calibration object. This should only be called
+ * once. The struct will reset automatically in accel_cal_accumulate when
+ * a new calibration is computed.
+ *
+ * @param cal Pointer to the accel_cal struct to reset.
+ */
+void accel_cal_reset(struct accel_cal *cal);
+
+/**
+ * Add new reading to the accelerometer calibration.
+ *
+ * @param cal Pointer to the accel_cal struct to update.
+ * @param sample_time The timestamp when the sample was taken.
+ * @param x X component of the new reading.
+ * @param y Y component of the new reading.
+ * @param z Z component of the new reading.
+ * @param temp The sensor's internal temperature in degrees C.
+ * @return True if a new bias is available.
+ */
+bool accel_cal_accumulate(struct accel_cal *cal, uint32_t sample_time, fp_t x,
+			  fp_t y, fp_t z, fp_t temp);
+
+#endif /* __CROS_EC_ACCEL_CAL_H */