examples: cleanup examples directory

Following changes are done as a part of cleanup:

1. Moved the platform specific `C` examples from top level examples/
directory to platform/ subdirectory and renamed helloedison.c to
gpio_edison.c

2. C specific examples are moved to a new c/ subdirectory. As a part
of this process, examples are modified to follow same standards
and few new examples are also added.

3. Include the newly added C examples to relevant API documentation

4. Ran clang-format for all source files in c/, c++/, platform/
subdirectories

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

examples/c/i2c_mpu6050.c

@@ -0,0 +1,170 @@
+/*
+ * Author: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
+ * Copyright (c) 2018, Linaro Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * Example usage: Outputs Accelerometer and Gyroscope value from MPU6050 recursively.
+ *                Press Ctrl+C to exit.
+ *
+ */
+
+/* standard headers */
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+/* mraa header */
+#include "mraa/i2c.h"
+
+#define I2C_BUS 0
+
+/* register definitions */
+#define MPU6050_ADDR 0x68
+#define MPU6050_REG_PWR_MGMT_1 0x6b
+#define MPU6050_REG_RAW_ACCEL_X 0x3b
+#define MPU6050_REG_RAW_ACCEL_Y 0x3d
+#define MPU6050_REG_RAW_ACCEL_Z 0x3f
+#define MPU6050_REG_RAW_GYRO_X 0x43
+#define MPU6050_REG_RAW_GYRO_Y 0x45
+#define MPU6050_REG_RAW_GYRO_Z 0x47
+
+/* bit definitions */
+#define MPU6050_RESET 0x80
+#define MPU6050_SLEEP (1 << 6)
+#define MPU6050_PLL_GYRO_X (1 << 1)
+
+/* accelerometer scale factor for (+/-)2g */
+#define MPU6050_ACCEL_SCALE 16384.0
+
+/* gyroscope scale factor for (+/-)250/s */
+#define MPU6050_GYRO_SCALE 131.0
+
+volatile sig_atomic_t flag = 1;
+
+void
+sig_handler(int signum)
+{
+    if (signum == SIGINT) {
+        fprintf(stdout, "Exiting...\n");
+        flag = 0;
+    }
+}
+
+int16_t
+i2c_read_word(mraa_i2c_context dev, uint8_t command)
+{
+    return be16toh(mraa_i2c_read_word_data(dev, command));
+}
+
+int
+main(void)
+{
+    mraa_result_t status = MRAA_SUCCESS;
+    mraa_i2c_context i2c;
+    uint8_t data;
+    int16_t accel_data[3];
+    int16_t gyro_data[3];
+    int ret;
+
+    /* install signal handler */
+    signal(SIGINT, sig_handler);
+
+    /* initialize mraa for the platform (not needed most of the times) */
+    mraa_init();
+
+    //! [Interesting]
+    /* initialize I2C bus */
+    i2c = mraa_i2c_init(I2C_BUS);
+    if (i2c == NULL) {
+        fprintf(stderr, "Failed to initialize I2C\n");
+        mraa_deinit();
+        return EXIT_FAILURE;
+    }
+
+    /* set slave address */
+    status = mraa_i2c_address(i2c, MPU6050_ADDR);
+    if (status != MRAA_SUCCESS) {
+        goto err_exit;
+    }
+
+    /* reset the sensor */
+    status = mraa_i2c_write_byte_data(i2c, MPU6050_RESET, MPU6050_REG_PWR_MGMT_1);
+    if (status != MRAA_SUCCESS) {
+        goto err_exit;
+    }
+
+    sleep(5);
+
+    /* configure power management register */
+    ret = mraa_i2c_read_byte_data(i2c, MPU6050_REG_PWR_MGMT_1);
+    if (ret == -1) {
+        return EXIT_FAILURE;
+    }
+
+    data = ret;
+    data |= MPU6050_PLL_GYRO_X;
+    data &= ~(MPU6050_SLEEP);
+
+    status = mraa_i2c_write_byte_data(i2c, data, MPU6050_REG_PWR_MGMT_1);
+    if (status != MRAA_SUCCESS) {
+        goto err_exit;
+    }
+
+    sleep(5);
+
+    while (flag) {
+        /* read raw accel data */
+        accel_data[0] = i2c_read_word(i2c, MPU6050_REG_RAW_ACCEL_X) / MPU6050_ACCEL_SCALE;
+        accel_data[1] = i2c_read_word(i2c, MPU6050_REG_RAW_ACCEL_Y) / MPU6050_ACCEL_SCALE;
+        accel_data[2] = i2c_read_word(i2c, MPU6050_REG_RAW_ACCEL_Z) / MPU6050_ACCEL_SCALE;
+
+        /* read raw gyro data */
+        gyro_data[0] = i2c_read_word(i2c, MPU6050_REG_RAW_GYRO_X) / MPU6050_GYRO_SCALE;
+        gyro_data[1] = i2c_read_word(i2c, MPU6050_REG_RAW_GYRO_Y) / MPU6050_GYRO_SCALE;
+        gyro_data[2] = i2c_read_word(i2c, MPU6050_REG_RAW_GYRO_Z) / MPU6050_GYRO_SCALE;
+
+        fprintf(stdout, "accel: x:%d y:%d z:%d\n", accel_data[0], accel_data[1], accel_data[2]);
+        fprintf(stdout, "gyro: x:%d y:%d z:%d\n\n", gyro_data[0], gyro_data[1], gyro_data[2]);
+
+        sleep(2);
+    }
+
+    /* stop i2c */
+    mraa_i2c_stop(i2c);
+
+    //! [Interesting]
+    /* deinitialize mraa for the platform (not needed most of the times) */
+    mraa_deinit();
+
+    return EXIT_SUCCESS;
+
+err_exit:
+    mraa_result_print(status);
+
+    /* stop i2c */
+    mraa_i2c_stop(i2c);
+
+    /* deinitialize mraa for the platform (not needed most of the times) */
+    mraa_deinit();
+
+    return EXIT_FAILURE;
+}