Diff: main.cpp

Revision:

0:7489bca92308

Child:

1:7f3b2be90495

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Tue Jan 31 19:07:30 2017 +0000
@@ -0,0 +1,229 @@
+/* K64F Accelerometer & Magnetometer
+
+Sample code for reading data from on-board FXOS8700CQ sensor
+
+Craig A. Evans
+Jan 2017
+
+*/
+
+#include "mbed.h"
+
+///////////// defines //////////////////////////////////
+
+// mbed API uses 8-bit addresses so need to left-shift 7-bit addresses by 1
+#define FXOS8700CQ_ADDR   (0x1D << 1)    // for K64F board
+// values from 13.2 datasheet
+#define FXOS8700CQ_STATUS 0x00
+#define FXOS8700CQ_WHO_AM_I 0x0D
+#define FXOS8700CQ_XYZ_DATA_CFG 0x0E
+#define FXOS8700CQ_CTRL_REG1 0x2A
+#define FXOS8700CQ_M_CTRL_REG1 0x5B
+#define FXOS8700CQ_M_CTRL_REG2 0x5C
+#define FXOS8700CQ_WHO_AM_I_VAL 0xC7
+#define FXOS8700CQ_READ_LEN 13
+
+// struct to hold 6 DOF values
+struct Data {
+    float ax;
+    float ay;
+    float az;
+    float mx;
+    float my;
+    float mz;
+};
+
+////////// mbed API objects ////////////////////////////
+
+// I2C connection for FXOS8700CQ accelerometer/magnetometer
+I2C fxos8700cq(I2C_SDA,I2C_SCL);  // PTE25/PTE24
+
+//////// function prototypes ///////////////////////////
+// setup accelerometer/magnetometer
+void init_fxos8700cq();
+// i2c primitive functions
+void send_byte_to_reg(char byte,char reg);
+char read_byte_from_reg(char reg);
+void read_bytes_from_reg(char reg,int number_of_bytes,char bytes[]);
+// FXOS8700CQ values
+Data get_values();
+
+///////// functions ////////////////////////////////////
+
+int main()
+{
+    printf("K64F FXOS8700CQ Example Code\n\n");
+    init_fxos8700cq();
+
+    while(1) {
+        
+        Data values = get_values();
+        
+        float mag_h = sqrt(values.mx*values.mx+
+                           values.my*values.my+
+                           values.mz*values.mz);
+                           
+        printf("Mag = %f\n",mag_h);
+        
+        //printf("ax = %f ay = %f az = %f | mx = %f my = %f mz = %f\n"
+        //       ,values.ax, values.ay, values.az
+        //      ,values.mx, values.my, values.mz);
+        
+        wait(1.0);
+    }
+
+}
+
+// gets the status, acceleration and magnetometer data
+Data get_values()
+{
+    printf("Reading values...");
+    // 13 bytes - status plus 6 channels (2 bytes each)
+    // x,y,z for accelerometer and magnetometer
+    char data[FXOS8700CQ_READ_LEN];
+    read_bytes_from_reg(FXOS8700CQ_STATUS,FXOS8700CQ_READ_LEN,data);
+
+    // copy the 14 bit accelerometer byte data into 16 bit words
+    int acc_x = (int16_t)(((data[1] << 8) | data[2]))>> 2;
+    int acc_y = (int16_t)(((data[3] << 8) | data[4]))>> 2;
+    int acc_z = (int16_t)(((data[5] << 8) | data[6]))>> 2;
+
+    // copy the magnetometer byte data into 16 bit words
+    int mag_x = (int16_t) (data[7] << 8) | data[8];
+    int mag_y = (int16_t) (data[9] << 8) | data[10];
+    int mag_z = (int16_t) (data[11] << 8) | data[12];
+
+    Data values;  // struct to hold values
+
+    // 0.488 mg/LSB in 4 g mode (8.1 data sheet)
+    values.ax = 0.488e-3*acc_x;
+    values.ay = 0.488e-3*acc_y;
+    values.az = 0.488e-3*acc_z;
+
+    // the magnetometer sensitivity is fixed at 0.1 μT/LSB
+    values.mx = 0.1e-6*mag_x;
+    values.my = 0.1e-6*mag_y;
+    values.mz = 0.1e-6*mag_z;
+
+    printf("Done.\n");
+
+    return values;
+}
+
+/// primitive i2c functions ////
+
+// sends a byte to a specific register
+void send_byte_to_reg(char byte,char reg)
+{
+    char data[2];
+    data[0] = reg;
+    data[1] = byte;
+    // send the register address, followed by the data
+    int nack = fxos8700cq.write(FXOS8700CQ_ADDR,data,2);
+    if (nack)
+        error("No ACK");  // if we don't receive acknowledgement, flash error message
+}
+
+// reads a byte from a specific register
+char read_byte_from_reg(char reg)
+{
+    int nack = fxos8700cq.write(FXOS8700CQ_ADDR,&reg,1,true);  // send the register address to the slave
+    // true as need to send repeated start condition (5.10.1 datasheet)
+    // http://www.i2c-bus.org/repeated-start-condition/
+    if (nack)
+        error("No ACK");  // if we don't receive acknowledgement, flash error message
+
+    char rx;
+    nack = fxos8700cq.read(FXOS8700CQ_ADDR,&rx,1);  // read a byte from the register and store in buffer
+    if (nack)
+        error("No ACK");  // if we don't receive acknowledgement, flash error message
+
+    return rx;
+}
+
+// reads a series of bytes, starting from a specific register
+void read_bytes_from_reg(char reg,int number_of_bytes,char bytes[])
+{
+    int nack = fxos8700cq.write(FXOS8700CQ_ADDR,&reg,1,true);  // send the slave write address and the configuration register address
+    // true as need to send repeated start condition (5.10.1 datasheet)
+    // http://www.i2c-bus.org/repeated-start-condition/
+
+    if (nack)
+        error("No ACK");  // if we don't receive acknowledgement, flash error message
+
+    nack = fxos8700cq.read(FXOS8700CQ_ADDR,bytes,number_of_bytes);  // read bytes
+    if (nack)
+        error("No ACK");  // if we don't receive acknowledgement, flash error message
+
+}
+
+/// init functions /////
+
+// based on 13.4 in datasheet - 200 Hz hybrid mode (both acc and mag)
+void init_fxos8700cq()
+{
+    printf("Initialising....\n");
+
+    // i2c fast-mode - 10.1.1 data sheet
+    fxos8700cq.frequency(400000);
+
+    // the device has an ID number so we check the value to ensure the correct
+    // drive is on the i2c bus
+    char data = read_byte_from_reg(FXOS8700CQ_WHO_AM_I);
+    if (data != FXOS8700CQ_WHO_AM_I_VAL) { // if correct ID not found, hang and flash error message
+        error("Not correct ID");
+    }
+
+    printf("Read correct WHO_AM_I value: 0x%X\n",data);
+
+    // write 0000 0000 = 0x00 to accelerometer control register 1 to place
+    // FXOS8700CQ into standby
+    // [7-1] = 0000 000
+    // [0]: active=0
+    data = 0x00;
+    send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1);
+
+    // write 0001 1111 = 0x1F to magnetometer control register 1
+    // [7]: m_acal=0: auto calibration disabled
+    // [6]: m_rst=0: no one-shot magnetic reset
+    // [5]: m_ost=0: no one-shot magnetic measurement
+    // [4-2]: m_os=111=7: 8x oversampling (for 200Hz) to reduce magnetometer noise
+    // [1-0]: m_hms=11=3: select hybrid mode with accel and magnetometer active
+    data = 0x1F;
+    send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG1);
+
+    // write 0010 0000 = 0x20 to magnetometer control register 2
+    // [7]: reserved
+    // [6]: reserved
+    // [5]: hyb_autoinc_mode=1 to map the magnetometer registers to follow
+    // the accelerometer registers
+    // [4]: m_maxmin_dis=0 to retain default min/max latching even though not used
+    // [3]: m_maxmin_dis_ths=0
+    // [2]: m_maxmin_rst=0
+    // [1-0]: m_rst_cnt=00 to enable magnetic reset each cycle
+    data = 0x20;
+    send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG2);
+
+    // write 0000 0001= 0x01 to XYZ_DATA_CFG register
+    // [7]: reserved
+    // [6]: reserved
+    // [5]: reserved
+    // [4]: hpf_out=0
+    // [3]: reserved
+    // [2]: reserved
+    // [1-0]: fs=01 for accelerometer range of +/-4g range with 0.488mg/LSB
+    data = 0x01;
+    send_byte_to_reg(data,FXOS8700CQ_XYZ_DATA_CFG);
+
+    // write 0000 1101 = 0x0D to accelerometer control register 1
+    // [7-6]: aslp_rate=00
+    // [5-3]: dr=001 for 200Hz data rate (when in hybrid mode)
+    // [2]: lnoise=1 for low noise mode
+    // [1]: f_read=0 for normal 16 bit reads
+    // [0]: active=1 to take the part out of standby and enable sampling
+    data = 0x0D;
+    send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1);
+
+    printf("Initialisation complete!\n");
+
+}
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