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      1 /*
      2  * Author: Brendan Le Foll <brendan.le.foll (at) intel.com>
      3  * Copyright (c) 2014 Intel Corporation.
      4  *
      5  * Permission is hereby granted, free of charge, to any person obtaining
      6  * a copy of this software and associated documentation files (the
      7  * "Software"), to deal in the Software without restriction, including
      8  * without limitation the rights to use, copy, modify, merge, publish,
      9  * distribute, sublicense, and/or sell copies of the Software, and to
     10  * permit persons to whom the Software is furnished to do so, subject to
     11  * the following conditions:
     12  *
     13  * The above copyright notice and this permission notice shall be
     14  * included in all copies or substantial portions of the Software.
     15  *
     16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     17  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     18  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     19  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
     20  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
     21  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
     22  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     23  */
     24 
     25 #include "mraa.h"
     26 #include "math.h"
     27 
     28 #define MAX_BUFFER_LENGTH 6
     29 #define HMC5883L_I2C_ADDR 0x1E
     30 
     31 // configuration registers
     32 #define HMC5883L_CONF_REG_A 0x00
     33 #define HMC5883L_CONF_REG_B 0x01
     34 
     35 // mode register
     36 #define HMC5883L_MODE_REG 0x02
     37 
     38 // data register
     39 #define HMC5883L_X_MSB_REG 0
     40 #define HMC5883L_X_LSB_REG 1
     41 #define HMC5883L_Z_MSB_REG 2
     42 #define HMC5883L_Z_LSB_REG 3
     43 #define HMC5883L_Y_MSB_REG 4
     44 #define HMC5883L_Y_LSB_REG 5
     45 #define DATA_REG_SIZE 6
     46 
     47 // status register
     48 #define HMC5883L_STATUS_REG 0x09
     49 
     50 // ID registers
     51 #define HMC5883L_ID_A_REG 0x0A
     52 #define HMC5883L_ID_B_REG 0x0B
     53 #define HMC5883L_ID_C_REG 0x0C
     54 
     55 #define HMC5883L_CONT_MODE 0x00
     56 #define HMC5883L_DATA_REG 0x03
     57 
     58 // scales
     59 #define GA_0_88_REG 0x00 << 5
     60 #define GA_1_3_REG 0x01 << 5
     61 #define GA_1_9_REG 0x02 << 5
     62 #define GA_2_5_REG 0x03 << 5
     63 #define GA_4_0_REG 0x04 << 5
     64 #define GA_4_7_REG 0x05 << 5
     65 #define GA_5_6_REG 0x06 << 5
     66 #define GA_8_1_REG 0x07 << 5
     67 
     68 // digital resolutions
     69 #define SCALE_0_73_MG 0.73
     70 #define SCALE_0_92_MG 0.92
     71 #define SCALE_1_22_MG 1.22
     72 #define SCALE_1_52_MG 1.52
     73 #define SCALE_2_27_MG 2.27
     74 #define SCALE_2_56_MG 2.56
     75 #define SCALE_3_03_MG 3.03
     76 #define SCALE_4_35_MG 4.35
     77 
     78 int
     79 main(int argc, char** argv)
     80 {
     81     mraa_init();
     82     float direction = 0;
     83     int16_t x = 0, y = 0, z = 0;
     84     uint8_t rx_tx_buf[MAX_BUFFER_LENGTH];
     85 
     86     //! [Interesting]
     87     mraa_i2c_context i2c;
     88     i2c = mraa_i2c_init(0);
     89 
     90     mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
     91     rx_tx_buf[0] = HMC5883L_CONF_REG_B;
     92     rx_tx_buf[1] = GA_1_3_REG;
     93     mraa_i2c_write(i2c, rx_tx_buf, 2);
     94     //! [Interesting]
     95 
     96     mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
     97     rx_tx_buf[0] = HMC5883L_MODE_REG;
     98     rx_tx_buf[1] = HMC5883L_CONT_MODE;
     99     mraa_i2c_write(i2c, rx_tx_buf, 2);
    100 
    101     for (;;) {
    102 #if 0
    103         int i = 0;
    104         //alternative, equivalent method which helps to understand exactly what
    105         //the below does
    106         mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    107         for (i = 0; i < DATA_REG_SIZE; i++) {
    108             mraa_i2c_read_byte_data(i2c, HMC5883L_DATA_REG+i);
    109         }
    110 #endif
    111         // first 'select' the register we want to read from
    112         mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    113         mraa_i2c_write_byte(i2c, HMC5883L_DATA_REG);
    114 
    115         // then we read from that register incrementing with every read the
    116         // chosen register
    117         mraa_i2c_address(i2c, HMC5883L_I2C_ADDR);
    118         // this call behaves very similarly to the Wire receive() call
    119         mraa_i2c_read(i2c, rx_tx_buf, DATA_REG_SIZE);
    120 
    121         x = (rx_tx_buf[HMC5883L_X_MSB_REG] << 8) | rx_tx_buf[HMC5883L_X_LSB_REG];
    122         z = (rx_tx_buf[HMC5883L_Z_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Z_LSB_REG];
    123         y = (rx_tx_buf[HMC5883L_Y_MSB_REG] << 8) | rx_tx_buf[HMC5883L_Y_LSB_REG];
    124 
    125         // scale and calculate direction
    126         direction = atan2(y * SCALE_0_92_MG, x * SCALE_0_92_MG);
    127 
    128         // check if the signs are reversed
    129         if (direction < 0)
    130             direction += 2 * M_PI;
    131 
    132         printf("Compass scaled data x : %f, y : %f, z : %f\n", x * SCALE_0_92_MG, y * SCALE_0_92_MG,
    133                z * SCALE_0_92_MG);
    134         printf("Heading : %f\n", direction * 180 / M_PI);
    135     }
    136 }
    137