James Heavey
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EL17JH
FINAL VERSION
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FXOS8700CQ.cpp
00001 /* FXOS8700CQ Library 00002 00003 Sample code from ELEC2645 - demonstrates how to create a library 00004 for the K64F on-board accelerometer and magnetometer 00005 00006 (c) Craig A. Evans, University of Leeds, Jan 2017 00007 00008 */ 00009 00010 #include "FXOS8700CQ.h" 00011 00012 // constructor is called when the object is created - use it to set pins and frequency 00013 FXOS8700CQ::FXOS8700CQ(PinName sda, PinName scl) 00014 { 00015 i2c = new I2C(sda,scl); // create new I2C instance and initialise 00016 } 00017 00018 // destructor is called when the object goes out of scope 00019 FXOS8700CQ::~FXOS8700CQ() 00020 { 00021 delete i2c; // free memory 00022 } 00023 00024 // based on 13.4 in datasheet - 200 Hz hybrid mode (both acc and mag) 00025 void FXOS8700CQ::init() 00026 { 00027 // i2c fast-mode - 10.1.1 data sheet 00028 i2c->frequency(400000); // I2C Fast Mode - 400kHz 00029 00030 // the device has an ID number so we check the value to ensure the correct 00031 // drive is on the i2c bus 00032 char data = read_byte_from_reg(FXOS8700CQ_WHO_AM_I); 00033 if (data != FXOS8700CQ_WHO_AM_I_VAL) { // if correct ID not found, hang and flash error message 00034 error("Incorrect ID!"); 00035 } 00036 00037 // write 0000 0000 = 0x00 to accelerometer control register 1 to place 00038 // FXOS8700CQ into standby 00039 // [7-1] = 0000 000 00040 // [0]: active=0 00041 data = 0x00; 00042 send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1); 00043 00044 // write 0001 1111 = 0x1F to magnetometer control register 1 00045 // [7]: m_acal=0: auto calibration disabled 00046 // [6]: m_rst=0: no one-shot magnetic reset 00047 // [5]: m_ost=0: no one-shot magnetic measurement 00048 // [4-2]: m_os=111=7: 8x oversampling (for 200Hz) to reduce magnetometer noise 00049 // [1-0]: m_hms=11=3: select hybrid mode with accel and magnetometer active 00050 data = 0x1F; 00051 send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG1); 00052 00053 // write 0010 0000 = 0x20 to magnetometer control register 2 00054 // [7]: reserved 00055 // [6]: reserved 00056 // [5]: hyb_autoinc_mode=1 to map the magnetometer registers to follow 00057 // the accelerometer registers 00058 // [4]: m_maxmin_dis=0 to retain default min/max latching even though not used 00059 // [3]: m_maxmin_dis_ths=0 00060 // [2]: m_maxmin_rst=0 00061 // [1-0]: m_rst_cnt=00 to enable magnetic reset each cycle 00062 data = 0x20; 00063 send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG2); 00064 00065 // write 0000 0001= 0x01 to XYZ_DATA_CFG register 00066 // [7]: reserved 00067 // [6]: reserved 00068 // [5]: reserved 00069 // [4]: hpf_out=0 00070 // [3]: reserved 00071 // [2]: reserved 00072 // [1-0]: fs=01 for accelerometer range of +/-4g range with 0.488mg/LSB 00073 data = 0x01; 00074 send_byte_to_reg(data,FXOS8700CQ_XYZ_DATA_CFG); 00075 00076 // write 0000 1101 = 0x0D to accelerometer control register 1 00077 // [7-6]: aslp_rate=00 00078 // [5-3]: dr=001 for 200Hz data rate (when in hybrid mode) 00079 // [2]: lnoise=1 for low noise mode 00080 // [1]: f_read=0 for normal 16 bit reads 00081 // [0]: active=1 to take the part out of standby and enable sampling 00082 data = 0x0D; 00083 send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1); 00084 00085 } 00086 00087 Data FXOS8700CQ::get_values() 00088 { 00089 // 13 bytes - status plus 6 channels (2 bytes each) 00090 // x,y,z for accelerometer and magnetometer 00091 char data[FXOS8700CQ_READ_LEN]; 00092 read_bytes_from_reg(FXOS8700CQ_STATUS,FXOS8700CQ_READ_LEN,data); 00093 00094 // copy the 14 bit accelerometer byte data into 16 bit words 00095 int acc_x = (int16_t)(((data[1] << 8) | data[2]))>> 2; 00096 int acc_y = (int16_t)(((data[3] << 8) | data[4]))>> 2; 00097 int acc_z = (int16_t)(((data[5] << 8) | data[6]))>> 2; 00098 00099 // copy the magnetometer byte data into 16 bit words 00100 int mag_x = (int16_t) (data[7] << 8) | data[8]; 00101 int mag_y = (int16_t) (data[9] << 8) | data[10]; 00102 int mag_z = (int16_t) (data[11] << 8) | data[12]; 00103 00104 Data values; // struct to hold values 00105 00106 // 0.488 mg/LSB in 4 g mode (8.1 data sheet) 00107 values.ax = 0.488e-3*acc_x; 00108 values.ay = 0.488e-3*acc_y; 00109 values.az = 0.488e-3*acc_z; 00110 00111 // the magnetometer sensitivity is fixed at 0.1 μT/LSB 00112 values.mx = 0.1e-6*mag_x; 00113 values.my = 0.1e-6*mag_y; 00114 values.mz = 0.1e-6*mag_z; 00115 00116 return values; 00117 } 00118 00119 void FXOS8700CQ::send_byte_to_reg(char byte,char reg) 00120 { 00121 char data[2]; 00122 data[0] = reg; 00123 data[1] = byte; 00124 // send the register address, followed by the data 00125 int nack = i2c->write(FXOS8700CQ_ADDR,data,2); 00126 if (nack) 00127 error("No acknowledgement received!"); // if we don't receive acknowledgement, send error message 00128 00129 } 00130 00131 // reads a byte from a specific register 00132 char FXOS8700CQ::read_byte_from_reg(char reg) 00133 { 00134 int nack = i2c->write(FXOS8700CQ_ADDR,®,1,true); // send the register address to the slave 00135 // true as need to send repeated start condition (5.10.1 datasheet) 00136 // http://www.i2c-bus.org/repeated-start-condition/ 00137 if (nack) 00138 error("No acknowledgement received!"); // if we don't receive acknowledgement, send error message 00139 00140 char rx; 00141 nack = i2c->read(FXOS8700CQ_ADDR,&rx,1); // read a byte from the register and store in buffer 00142 if (nack) 00143 error("No acknowledgement received!"); // if we don't receive acknowledgement, send error message 00144 00145 return rx; 00146 } 00147 00148 // reads a series of bytes, starting from a specific register 00149 void FXOS8700CQ::read_bytes_from_reg(char reg,int number_of_bytes,char bytes[]) 00150 { 00151 int nack = i2c->write(FXOS8700CQ_ADDR,®,1,true); // send the slave write address and the configuration register address 00152 // true as need to send repeated start condition (5.10.1 datasheet) 00153 // http://www.i2c-bus.org/repeated-start-condition/ 00154 00155 if (nack) 00156 error("No acknowledgement received!"); // if we don't receive acknowledgement, send error message 00157 00158 nack = i2c->read(FXOS8700CQ_ADDR,bytes,number_of_bytes); // read bytes 00159 if (nack) 00160 error("No acknowledgement received!"); // if we don't receive acknowledgement, send error message 00161 00162 } 00163 00164 float FXOS8700CQ::get_roll_angle() 00165 { 00166 Data values = get_values(); 00167 float roll_rad = atan2(values.ay,values.az); 00168 return roll_rad*(360/3.14159265); 00169 } 00170 00171 float FXOS8700CQ::get_pitch_angle() 00172 { 00173 Data values = get_values(); 00174 float pitch_rad = atan2(-values.ax,sqrt((values.ay * values.ay) + (values.az * values.az))); 00175 return pitch_rad*(360/3.14159265); 00176 }
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