Diff: MMA8452Q.cpp

Revision:

0:b3305e3c9e73

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MMA8452Q.cpp	Thu Oct 19 12:53:02 2017 +0000
@@ -0,0 +1,175 @@
+// Library for our MMA8452Q 3-axis accelerometer
+// Based on the MMA8452Q Arduino Library by Jim Lindblom (SparkFun Electronics)
+
+#include "mbed.h"
+#include "MMA8452Q.h"
+
+// Constructor
+MMA8452Q::MMA8452Q(PinName sda, PinName scl, int addr) : m_i2c(sda, scl), m_addr(addr)
+{
+    // Initialize members
+    scale = DEFAULT_FSR;    
+}
+
+// Destructor
+MMA8452Q::~MMA8452Q()
+{
+
+}
+
+// Initialization
+bool MMA8452Q::init()
+{
+    // Check to make sure the chip's ID matches the factory ID
+    uint8_t c = readRegister(REG_WHO_AM_I);
+    if( c != FACTORY_ID ) {
+        return false;
+    }
+
+    // Set default scale and data rate
+    standby();
+    setScale(DEFAULT_FSR);
+    setODR(DEFAULT_ODR);
+    active();
+
+    return true;
+}
+
+// Set the full-scale range for x, y, and z data
+void MMA8452Q::setScale(uint8_t fsr)
+{
+    uint8_t config = readRegister(REG_XYZ_DATA_CFG);
+    scale = fsr;
+    config &= 0xFC;                     // Mask out FSR bits
+    fsr = fsr >> 2;                     // Trick to translate scale to FSR bits
+    fsr &= 0x03;                        // Mask out acceptable FSRs
+    config |= fsr;                      // Write FSR bits to config byte
+    writeRegister(REG_XYZ_DATA_CFG, config);              // Write config back to register
+}
+
+// Set the Output Data Rate
+void MMA8452Q::setODR(uint8_t odr)
+{
+    uint8_t ctrl = readRegister(REG_CTRL_REG1);
+    ctrl &= 0xCF;                       // Mask out data rate bits
+    odr &= 0x07;                        // Mask out acceptable ODRs
+    ctrl |= (odr << 3);                 // Write ODR bits to control byte
+    writeRegister(REG_CTRL_REG1, ctrl); // Write control back to register
+}
+
+// Set accelerometer into standby mode
+void MMA8452Q::standby()
+{
+    uint8_t c = readRegister(REG_CTRL_REG1);
+    c &= ~(0x01);                       // Clear bit 0 to go into standby
+    writeRegister(REG_CTRL_REG1, c);    // Write back to CONTROL register
+}
+
+// Set accelerometer into active mode
+void MMA8452Q::active()
+{
+    uint8_t c = readRegister(REG_CTRL_REG1);
+    c |= 0x01;                          // Set bit 0 to go into active mode
+    writeRegister(REG_CTRL_REG1, c);    // Write back to CONTROL register
+}
+
+// Read X registers
+float MMA8452Q::readX()
+{
+    int16_t x = 0;
+    float cx = 0;
+
+    // Read MSB and LSB from X registers
+    x = readRegister(OUT_X_MSB);
+    x = x << 8;
+    x |= readRegister(OUT_X_LSB);
+    x = x >> 4;
+
+    // Calculate human readable X
+    cx = (float)x / (float)2048 * (float)(scale);
+
+    return cx;
+}
+
+// Read Y registers
+float MMA8452Q::readY()
+{
+    int16_t y = 0;
+    float cy = 0;
+
+    // Read MSB and LSB from Y registers
+    y = readRegister(OUT_Y_MSB);
+    y = y << 8;
+    y |= readRegister(OUT_Y_LSB);
+    y = y >> 4;
+
+    // Calculate human readable Y
+    cy = (float)y / (float)2048 * (float)(scale);
+
+    return cy;
+}
+
+// Read Z registers
+float MMA8452Q::readZ()
+{
+    int16_t z = 0;
+    float cz = 0;
+
+    // Read MSB and LSB from Z registers
+    z = readRegister(OUT_Z_MSB);
+    z = z << 8;
+    z |= readRegister(OUT_Z_LSB);
+    z = z >> 4;
+
+    // Calculate human readable Z
+    cz = (float)z / (float)2048 * (float)(scale);
+
+    return cz;
+}
+
+// Raw read register over I2C
+uint8_t MMA8452Q::readRegister(uint8_t reg)
+{
+    uint8_t dev_addr;
+    uint8_t data;
+
+    // I2C address are bits [6..1] in the transmitted byte, so we shift by 1
+    dev_addr = m_addr << 1;
+
+    // Write device address with a trailing 'write' bit
+    m_i2c.start();
+    m_i2c.write(dev_addr & 0xFE);
+
+    // Write register address
+    m_i2c.write(reg);
+
+    // Write a start bit and device address with a trailing 'read' bit
+    m_i2c.start();
+    m_i2c.write(dev_addr | 0x01);
+
+    // Read single byte from I2C device
+    data = m_i2c.read(0);
+    m_i2c.stop();
+
+    return data;
+}
+
+// Raw write data to a register over I2C    
+void MMA8452Q::writeRegister(uint8_t reg, uint8_t data)
+{
+    uint8_t dev_addr;
+
+    // I2C address are bits [6..1] in the transmitted byte, so we shift by 1
+    dev_addr = m_addr << 1;
+
+    // Write device address with a trailing 'write' bit
+    m_i2c.start();
+    m_i2c.write(dev_addr & 0xFE);
+
+    // Write register address
+    m_i2c.write(reg);
+
+    // Write the data to the register
+    m_i2c.write(data);
+    m_i2c.stop();
+}
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