/*
 * Author: Brendan Le Foll <brendan.le.foll@intel.com>
 * Copyright (c) 2014 Intel Corporation.
 *
 * SPDX-License-Identifier: MIT
 *
 * Example usage: Outputs X,Y,Z co-ordinates and direction recursively using
 *                HMC5883L. Press Ctrl+C to exit.
 *
 */

/* standard headers */
#include <math.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/* mraa header */
#include "mraa/i2c.h"

#define MAX_BUFFER_LENGTH 6
#define HMC5883L_I2C_ADDR 0x1E

/* configuration registers */
#define HMC5883L_CONF_REG_A 0x00
#define HMC5883L_CONF_REG_B 0x01

/* mode register */
#define HMC5883L_MODE_REG 0x02

/* data register */
#define HMC5883L_X_MSB_REG 0
#define HMC5883L_X_LSB_REG 1
#define HMC5883L_Z_MSB_REG 2
#define HMC5883L_Z_LSB_REG 3
#define HMC5883L_Y_MSB_REG 4
#define HMC5883L_Y_LSB_REG 5
#define DATA_REG_SIZE 6

/* status register */
#define HMC5883L_STATUS_REG 0x09

/* ID registers */
#define HMC5883L_ID_A_REG 0x0A
#define HMC5883L_ID_B_REG 0x0B
#define HMC5883L_ID_C_REG 0x0C

#define HMC5883L_CONT_MODE 0x00
#define HMC5883L_DATA_REG 0x03

/* scales */
#define GA_0_88_REG 0x00 << 5
#define GA_1_3_REG 0x01 << 5
#define GA_1_9_REG 0x02 << 5
#define GA_2_5_REG 0x03 << 5
#define GA_4_0_REG 0x04 << 5
#define GA_4_7_REG 0x05 << 5
#define GA_5_6_REG 0x06 << 5
#define GA_8_1_REG 0x07 << 5

/* digital resolutions */
#define SCALE_0_73_MG 0.73
#define SCALE_0_92_MG 0.92
#define SCALE_1_22_MG 1.22
#define SCALE_1_52_MG 1.52
#define SCALE_2_27_MG 2.27
#define SCALE_2_56_MG 2.56
#define SCALE_3_03_MG 3.03
#define SCALE_4_35_MG 4.35

#define I2C_BUS 0

volatile sig_atomic_t flag = 1;

void
sig_handler(int signum)
{
    if (signum == SIGINT) {
        fprintf(stdout, "Exiting...\n");
        flag = 0;
    }
}

int
main(void)
{
    mraa_result_t status = MRAA_SUCCESS;
    mraa_i2c_context i2c;
    float direction = 0;
    int16_t x = 0, y = 0, z = 0;
    uint8_t rx_tx_buf[MAX_BUFFER_LENGTH];

    /* install signal handler */
    signal(SIGINT, sig_handler);

    /* initialize mraa for the platform (not needed most of the times) */
    mraa_init();

    //! [Interesting]
    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, HMC5883L_I2C_ADDR);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* set device gain */
    rx_tx_buf[0] = HMC5883L_CONF_REG_B;
    rx_tx_buf[1] = GA_1_3_REG;

    status = mraa_i2c_write(i2c, rx_tx_buf, 2);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    /* set continuous mode */
    rx_tx_buf[0] = HMC5883L_MODE_REG;
    rx_tx_buf[1] = HMC5883L_CONT_MODE;

    status = mraa_i2c_write(i2c, rx_tx_buf, 2);
    if (status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while (flag) {
#if 0
        int i = 0;
        /*
         * alternative, equivalent method which helps to understand exactly what
         * the below does
         */
        mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        for (i = 0; i < DATA_REG_SIZE; i++) {
            mraa_i2c_read_byte_data(i2c, HMC5883L_DATA_REG+i);
        }
#endif
        /* select data register to read */
        status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        status = mraa_i2c_write_byte(i2c, HMC5883L_DATA_REG);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        /* do a incremental read from the chosen address */
        status = mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
        if (status != MRAA_SUCCESS) {
            goto err_exit;
        }

        /* this call behaves very similarly to the Wire receive() call */
        mraa_i2c_read(i2c, rx_tx_buf, DATA_REG_SIZE);

        x = (rx_tx_buf[HMC5883L_X_MSB_REG] << 8) | rx_tx_buf[HMC5883L_X_LSB_REG];
        z = (rx_tx_buf[HMC5883L_Z_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Z_LSB_REG];
        y = (rx_tx_buf[HMC5883L_Y_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Y_LSB_REG];

        /* scale and calculate direction */
        direction = atan2(y * SCALE_0_92_MG, x * SCALE_0_92_MG);

        /* check if the signs are reversed */
        if (direction < 0) {
            direction += 2 * M_PI;
        }

        fprintf(stdout, "Compass scaled data x : %f, y : %f, z : %f\n", x * SCALE_0_92_MG,
                y * SCALE_0_92_MG, z * SCALE_0_92_MG);
        fprintf(stdout, "Heading : %f\n", direction * 180 / M_PI);

        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;
}