Preliminary driver for AK8975

Will wait for the delivery of the physical chips to test.

Author: pimvanpelt

src/mgos_imu_ak8975.c

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+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "mgos.h"
+#include "mgos_i2c.h"
+#include "mgos_imu_ak8975.h"
+
+bool mgos_imu_ak8975_detect(struct mgos_imu_mag *dev) {
+  int device_id;
+
+  if (!dev) {
+    return false;
+  }
+
+  device_id = mgos_i2c_read_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_WHO_AM_I);
+  if (device_id == MGOS_AK8975_DEVID) {
+    return true;
+  }
+  LOG(LL_ERROR, ("Failed to detect AK8975 at I2C 0x%02x (device_id=0x%02x)", dev->i2caddr, device_id));
+  return false;
+}
+
+bool mgos_imu_ak8975_create(struct mgos_imu_mag *dev) {
+  if (!dev) {
+    return false;
+  }
+
+  // Reset
+  mgos_i2c_write_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_CNTL, 0x00);
+  mgos_usleep(10000);
+
+  // Fuse ROM access mode
+  mgos_i2c_write_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_CNTL, 0x0F);
+  mgos_usleep(10000);
+
+  uint8_t data[3];
+  if (!mgos_i2c_read_reg_n(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_ASAX, 3, data)) {
+    LOG(LL_ERROR, ("Could not read magnetometer adjustment registers"));
+    return false;
+  }
+  dev->bias[0] = (float)(data[0] - 128) / 256. + 1.;
+  dev->bias[1] = (float)(data[1] - 128) / 256. + 1.;
+  dev->bias[2] = (float)(data[2] - 128) / 256. + 1.;
+
+  LOG(LL_DEBUG, ("Magnetometer adjustment bias %.2f %.2f %.2f", dev->bias[0], dev->bias[1], dev->bias[2]));
+
+  // Reset
+  mgos_i2c_write_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_CNTL, 0x00);
+  mgos_usleep(10000);
+
+  dev->scale = 1229.0 / 4096.0;
+
+  return true;
+}
+
+bool mgos_imu_ak8975_read(struct mgos_imu_mag *dev) {
+  uint8_t data[6];
+  int drdy;
+
+  if (!dev) {
+    return false;
+  }
+  
+  // Set single shot measurement
+  mgos_i2c_write_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_CNTL, 0x01);
+  mgos_usleep(9500);
+
+  // Check Data Ready
+  drdy = mgos_i2c_read_reg_b(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_ST1);
+  if (drdy != 0x01)
+    return false;
+
+  if (!mgos_i2c_read_reg_n(dev->i2c, dev->i2caddr, MGOS_AK8975_REG_XOUT_L, 6, data)) {
+    return false;
+  }
+
+  dev->mx = (data[1] << 8) | (data[0]);
+  dev->my = (data[3] << 8) | (data[2]);
+  dev->mz = (data[5] << 8) | (data[4]);
+  LOG(LL_DEBUG, ("mx=%d my=%d mz=%d", dev->mx, dev->my, dev->mz));
+  return true;
+}

src/mgos_imu_ak8975.h

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+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include "mgos.h"
+#include "mgos_imu_internal.h"
+
+#define MGOS_AK8975_DEFAULT_I2CADDR    (0x0C)
+#define MGOS_AK8975_DEVID              (0x48)
+
+// AK8975 Magnetometer Registers
+#define MGOS_AK8975_REG_WHO_AM_I       (0x00)
+#define MGOS_AK8975_REG_INFO           (0x01)
+#define MGOS_AK8975_REG_ST1            (0x02)
+#define MGOS_AK8975_REG_XOUT_L         (0x03)
+#define MGOS_AK8975_REG_ST2            (0x09)
+#define MGOS_AK8975_REG_CNTL           (0x0A)
+#define MGOS_AK8975_REG_ASAX           (0x10)
+#define MGOS_AK8975_REG_ASAY           (0x11)
+#define MGOS_AK8975_REG_ASAZ           (0x12)
+
+bool mgos_imu_ak8975_detect(struct mgos_imu_mag *dev);
+bool mgos_imu_ak8975_create(struct mgos_imu_mag *dev);
+bool mgos_imu_ak8975_read(struct mgos_imu_mag *dev);