Diff: IMU/Sensors/MPU9250/MPU9250.cpp

Revision:

10:14390c90c3f5

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/IMU/Sensors/MPU9250/MPU9250.cpp	Mon Aug 31 20:20:50 2015 +0000
@@ -0,0 +1,99 @@
+#include "MPU9250.h"
+
+MPU9250::MPU9250(PinName MOSI, PinName MISO, PinName SCLK, PinName CS) : spi(MOSI, MISO, SCLK), cs(CS) {
+    deselect();                         // chip must be deselected first
+    spi.format(8,0);                    // setup the spi for standard 8 bit data and SPI-Mode 0
+    spi.frequency(5e6);                 // with a 5MHz clock rate
+    
+    /*
+    last 3 Bits of|Accelerometer(Fs=1kHz) |Gyroscope 
+    MPU9250_CONFIG|Bandwidth(Hz)|Delay(ms)|Bandwidth(Hz)|Delay(ms)|Fs(kHz)
+    ------------------------------------------------------------------------- 
+    0             |260          |0        |256          |0.98     |8 
+    1             |184          |2.0      |188          |1.9      |1 
+    2             |94           |3.0      |98           |2.8      |1 
+    3             |44           |4.9      |42           |4.8      |1 
+    4             |21           |8.5      |20           |8.3      |1 
+    5             |10           |13.8     |10           |13.4     |1 
+    6             |5            |19.0     |5            |18.6     |1 
+    */
+    writeRegister8(MPU9250_CONFIG, 0x06);
+    writeRegister8(MPU9250_GYRO_CONFIG, 0x18);              // scales gyros range to +-2000dps
+    writeRegister8(MPU9250_ACCEL_CONFIG, 0x08);             // scales accelerometers range to +-4g
+}
+
+uint8_t MPU9250::getWhoami() {
+    return readRegister8(MPU9250_WHO_AM_I);
+}
+
+float MPU9250::getTemperature() {
+    int16_t data = readRegister16(MPU9250_TEMP_OUT_H);
+    return ((data - 21) / 333.87) + 21;                     // formula from register map p.33
+}
+
+void MPU9250::readGyro() {
+    int16_t rawGyro[3];
+    readRegister48(MPU9250_GYRO_XOUT_H, rawGyro);
+    
+    int16_t offsetGyro[3] = {-31, -15, -11};                // TODO: make better calibration
+    
+    for (int i = 0; i < 3; i++)
+        Gyro[i] = (rawGyro[i] - offsetGyro[i])*0.07;        // subtract offset from calibration and multiply unit factor to get degree per second (datasheet p.10)
+}
+
+void MPU9250::readAcc() {
+    int16_t rawAcc[3];
+    readRegister48(MPU9250_ACCEL_XOUT_H, rawAcc);
+    
+    int16_t offsetAcc[3] = {-120, -48, -438};                       // TODO: make better calibration
+    
+    for (int i = 0; i < 3; i++)
+        Acc[i] = (rawAcc[i] - offsetAcc[i])/8192.0;                // TODO: didn't care about units because IMU-algorithm just uses vector direction
+}
+
+// PRIVATE Methods ------------------------------------------------------------------------------------
+
+
+// SPI Interface --------------------------------------------------------------------------------------
+uint8_t MPU9250::readRegister8(uint8_t reg) {
+    uint8_t result;
+    readRegister(reg, &result, 1);
+    return result;
+}
+
+uint16_t MPU9250::readRegister16(uint8_t reg) {
+    uint8_t result[2];
+    readRegister(reg, result, 2);
+    return result[0]<<8 | result[1];                        // join 8-Bit pieces to 16-bit short integer
+}
+
+void MPU9250::readRegister48(uint8_t reg, int16_t *buffer) {
+    uint8_t result[6];
+    readRegister(reg, result, 6);
+    buffer[0] = (int16_t) (result[0] << 8 | result[1]);     // join 8-Bit pieces to 16-bit short integers
+    buffer[1] = (int16_t) (result[2] << 8 | result[3]);
+    buffer[2] = (int16_t) (result[4] << 8 | result[5]);
+}
+
+void MPU9250::writeRegister8(uint8_t reg, uint8_t buffer) {
+    writeRegister(reg, &buffer, 1);
+}
+
+void MPU9250::readRegister(uint8_t reg, uint8_t *buffer, int length) {
+    select();
+    spi.write(reg | 0x80);                                  // send the register address we want to read and the read flag
+    for(int i=0; i<length; i++)                             // get data
+        buffer[i] = spi.write(0x00);
+    deselect();
+}
+
+void MPU9250::writeRegister(uint8_t reg, uint8_t *buffer, int length) {
+    select();
+    spi.write(reg & ~0x80);                                 // send the register address we want to write and the write flag
+    for(int i=0; i<length; i++)                             // put data
+        spi.write(buffer[i]);
+    deselect();
+}
+
+void MPU9250::select() { cs = 0; }                          // set Cable Select pin low to start SPI transaction
+void MPU9250::deselect() { cs = 1; }                        // set Cable Select pin high to stop SPI transaction
\ No newline at end of file