common: Add magnetometer online calibration.

Code for hard iron calibration: Every seconds (or faster if enough
samples), find a sphere that fit the compass data.

Based on Android code.

BRANCH=smaug
BUG=chrome-os-partner:39900
TEST=Check hard-iron bias is removed. Works better outside.

Change-Id: Iab479d5113b6560b4f01b0fd87373d2eecdb9b54
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/299583
Reviewed-by: Anton Staaf <robotboy@chromium.org>

1 files changed, 85 insertions, 0 deletions

diff --git a/common/mat44.c b/common/mat44.c
new file mode 100644
index 0000000000..0f7f371461
--- /dev/null
+++ b/common/mat44.c
@@ -0,0 +1,85 @@
+/* Copyright 2015 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.
+ */
+
+#include "common.h"
+#include "mat44.h"
+#include "math.h"
+#include "util.h"
+
+#define K_EPSILON 1E-5f
+
+void mat44_decompose_lup(mat44_t LU, size4_t pivot)
+{
+	const size_t N = 4;
+	size_t i, j, k;
+
+	for (k = 0; k < N; ++k) {
+		float max = fabsf(LU[k][k]);
+		pivot[k] = k;
+		for (j = k + 1; j < N; ++j) {
+			if (max < fabsf(LU[j][k])) {
+				max = fabsf(LU[j][k]);
+				pivot[k] = j;
+			}
+		}
+
+		if (pivot[k] != k)
+			mat44_swap_rows(LU, k, pivot[k]);
+
+		if (fabsf(LU[k][k]) < K_EPSILON)
+			continue;
+
+		for (j = k + 1; j < N; ++j)
+			LU[k][j] /= LU[k][k];
+
+		for (i = k + 1; i < N; ++i)
+			for (j = k + 1; j < N; ++j)
+				LU[i][j] -= LU[i][k] * LU[k][j];
+	}
+}
+
+void mat44_swap_rows(mat44_t A, const size_t i, const size_t j)
+{
+	const size_t N = 4;
+	size_t k;
+
+	if (i == j)
+		return;
+
+	for (k = 0; k < N; ++k) {
+		float tmp = A[i][k];
+		A[i][k] = A[j][k];
+		A[j][k] = tmp;
+	}
+}
+
+void mat44_solve(mat44_t A, vec4_t x, const vec4_t b, const size4_t pivot)
+{
+	const size_t N = 4;
+	vec4_t b_copy;
+	size_t i, k;
+
+	memcpy(b_copy, b, sizeof(vec4_t));
+
+	for (k = 0; k < N; ++k) {
+		if (pivot[k] != k) {
+			float tmp = b_copy[k];
+			b_copy[k] = b_copy[pivot[k]];
+			b_copy[pivot[k]] = tmp;
+		}
+
+		x[k] = b_copy[k];
+		for (i = 0; i < k; ++i)
+			x[k] -= x[i] * A[k][i];
+		x[k] /= A[k][k];
+	}
+
+	for (k = N; k-- > 0;)
+		for (i = k + 1; i < N; ++i)
+			x[k] -= x[i] * A[k][i];
+}
+
+
+