Library for driving the MMA8452 accelerometer over I2C

Dependents:   MMA8452_Test MMA8452_Demo Dualing_Tanks IMU-Controlled_MP3_Player ... more

Here is a simple example:

#include "mbed.h"
#include "MMA8452.h"

int main() {
   Serial pc(USBTX,USBRX);
   pc.baud(115200);
   double x = 0, y = 0, z = 0;

   MMA8452 acc(p28, p27, 40000);
   acc.setBitDepth(MMA8452::BIT_DEPTH_12);
   acc.setDynamicRange(MMA8452::DYNAMIC_RANGE_4G);
   acc.setDataRate(MMA8452::RATE_100);
   
   while(1) {
      if(!acc.isXYZReady()) {
         wait(0.01);
         continue;
      }
      acc.readXYZGravity(&x,&y,&z);
      pc.printf("Gravities: %lf %lf %lf\r\n",x,y,z);
   }
}

An easy way to test that this actually works is to run the loop above and hold the MMA8452 parallel to the ground along the respective axis (and upsidedown in each axis). You will see 1G on the respective axis and 0G on the others.

MMA8452.cpp

Committer:
ashleymills
Date:
2014-03-07
Revision:
20:d55e9d7eb17e
Parent:
19:4d6cd7140a71
Child:
21:a92a632a0cc7

File content as of revision 20:d55e9d7eb17e:

// Authors: Ashley Mills, Nicholas Herriot
/* Copyright (c) 2013 Vodafone, MIT License
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include "MMA8452.h"
#include "mbed.h"

#ifdef MMA8452_DEBUG
// you need to define Serial pc(USBTX,USBRX) somewhere for the below line to make sense
extern Serial pc;
#define MMA8452_DBG(...) pc.printf(__VA_ARGS__); pc.printf("\r\n");
#else
#define MMA8452_DBG(...)
#endif

// Connect module at I2C address using I2C port pins sda and scl
MMA8452::MMA8452(PinName sda, PinName scl, int frequency) : _i2c(sda, scl) , _frequency(frequency) {
   MMA8452_DBG("Creating MMA8452");
   
   // set I2C frequency
   _i2c.frequency(_frequency);
   
   // setup read and write addresses for convenience
   _readAddress   = MMA8452_ADDRESS | 0x01;
   _writeAddress  = MMA8452_ADDRESS & 0xFE;
   
   // set some defaults
   _bitDepth = BIT_DEPTH_UNKNOWN;
   setBitDepth(BIT_DEPTH_12);
   _dynamicRange = DYNAMIC_RANGE_UNKNOWN;
   setDynamicRange(DYNAMIC_RANGE_2G);
   
   MMA8452_DBG("Done");
}


// Destroys instance
MMA8452::~MMA8452() {}

// Setting the control register bit 1 to true to activate the MMA8452
int MMA8452::activate() {
    // perform write and return error code
    return logicalORRegister(MMA8452_CTRL_REG_1,MMA8452_ACTIVE_MASK);
}

// Setting the control register bit 1 to 0 to standby the MMA8452
int MMA8452::standby() {
    // perform write and return error code
    return logicalANDRegister(MMA8452_CTRL_REG_1,MMA8452_STANDBY_MASK);
}

// this reads a register, applies a bitmask with logical AND, sets a value with logical OR,
// and optionally goes into and out of standby at the beginning and end of the function respectively
int MMA8452::maskAndApplyRegister(char reg, char mask, char value, int toggleActivation) {
   if(toggleActivation) {
       if(standby()) {
          return 1;
       }
   }
   
   // read from register
   char oldValue = 0;
   if(readRegister(reg,&oldValue)) {
      return 1;
   }
   
   // apply bitmask
   oldValue &= mask;
   
   // set value
   oldValue |= value;
   
   // write back to register
   if(writeRegister(reg,oldValue)) {
      return 1;
   }
   
   if(toggleActivation) {
       if(activate()) {
          return 1;
       }
   }
   return 0;
}

int MMA8452::setDynamicRange(DynamicRange range, int toggleActivation) {
   _dynamicRange = range;
   return maskAndApplyRegister(
      MMA8452_XYZ_DATA_CFG,
      MMA8452_DYNAMIC_RANGE_MASK,
      range,
      toggleActivation
   );
}

int MMA8452::setDataRate(DataRateHz dataRate, int toggleActivation) {
   return maskAndApplyRegister(
       MMA8452_CTRL_REG_1,
       MMA8452_DATA_RATE_MASK,
       dataRate<<MMA8452_DATA_RATE_MASK_SHIFT,
       toggleActivation
   );
}

int MMA8452::setBitDepth(BitDepth depth,int toggleActivation) {
   _bitDepth = depth;
   return maskAndApplyRegister(
      MMA8452_CTRL_REG_1,
      MMA8452_BIT_DEPTH_MASK,
      depth<<MMA8452_BIT_DEPTH_MASK_SHIFT,
      toggleActivation
   );
}

char MMA8452::getMaskedRegister(int reg, char mask) {
   char rval = 0;
   if(readRegister(reg,&rval)) {
      return 0;
   }
   return (rval&mask);
}

int MMA8452::isXYZReady() {
   return getMaskedRegister(MMA8452_STATUS,MMA8452_STATUS_ZYXDR_MASK)>0;
}

int MMA8452::isXReady() {
   return getMaskedRegister(MMA8452_STATUS,MMA8452_STATUS_XDR_MASK)>0;
}

int MMA8452::isYReady() {
   return getMaskedRegister(MMA8452_STATUS,MMA8452_STATUS_YDR_MASK)>0;
}

int MMA8452::isZReady() {
   return getMaskedRegister(MMA8452_STATUS,MMA8452_STATUS_ZDR_MASK)>0;
}


int MMA8452::getDeviceID(char *dst) {
   return readRegister(MMA8452_WHO_AM_I,dst);
}

int MMA8452::getStatus(char* dst) {
   return readRegister(MMA8452_STATUS,dst);
}

MMA8452::DynamicRange MMA8452::getDynamicRange() {
   char rval = 0;
   if(readRegister(MMA8452_XYZ_DATA_CFG,&rval)) {
      return MMA8452::DYNAMIC_RANGE_UNKNOWN;
   }
   rval &= (MMA8452_DYNAMIC_RANGE_MASK^0xFF);
   return (MMA8452::DynamicRange)rval;
}

MMA8452::DataRateHz MMA8452::getDataRate() {
   char rval = 0;
   if(readRegister(MMA8452_CTRL_REG_1,&rval)) {
      return MMA8452::RATE_UNKNOWN;
   }
   // logical AND with inverse of mask
   rval = rval&(MMA8452_DATA_RATE_MASK^0xFF);
   // shift back into position
   rval >>= MMA8452_DATA_RATE_MASK_SHIFT;
   return (MMA8452::DataRateHz)rval;
}

// Reads xyz
int MMA8452::readXYZRaw(char *dst) {
   if(_bitDepth==BIT_DEPTH_UNKNOWN) {
      return 1;
   }
   int readLen = 3;
   if(_bitDepth==BIT_DEPTH_12) {
      readLen = 6;
   }
   return readRegister(MMA8452_OUT_X_MSB,dst,readLen);
}

int MMA8452::readXRaw(char *dst) {
   if(_bitDepth==BIT_DEPTH_UNKNOWN) {
      return 1;
   }
   int readLen = 1;
   if(_bitDepth==BIT_DEPTH_12) {
      readLen = 2;
   }
   return readRegister(MMA8452_OUT_X_MSB,dst,readLen);
}

int MMA8452::readYRaw(char *dst) {
   if(_bitDepth==BIT_DEPTH_UNKNOWN) {
      return 1;
   }
   int readLen = 1;
   if(_bitDepth==BIT_DEPTH_12) {
      readLen = 2;
   }
   return readRegister(MMA8452_OUT_Y_MSB,dst,readLen);
}

int MMA8452::readZRaw(char *dst) {
   if(_bitDepth==BIT_DEPTH_UNKNOWN) {
      return 1;
   }
   int readLen = 1;
   if(_bitDepth==BIT_DEPTH_12) {
      readLen = 2;
   }
   return readRegister(MMA8452_OUT_Z_MSB,dst,readLen);
}

int MMA8452::readXYZCounts(int *x, int *y, int *z) {
   char buf[6];
   if(readXYZRaw((char*)&buf)) {
       return 1;
   }
   if(_bitDepth==BIT_DEPTH_12) {
     *x = twelveBitToSigned(&buf[0]);
     *y = twelveBitToSigned(&buf[2]);
     *z = twelveBitToSigned(&buf[4]);
   } else {
     *x = eightBitToSigned(&buf[0]);
     *y = eightBitToSigned(&buf[1]);
     *z = eightBitToSigned(&buf[2]);
   }
   
   return 0;
}

int MMA8452::readXCount(int *x) {
   char buf[2];
   if(readXRaw((char*)&buf)) {
       return 1;
   }
   if(_bitDepth==BIT_DEPTH_12) {
     *x = twelveBitToSigned(&buf[0]);
   } else {
     *x = eightBitToSigned(&buf[0]);
   }
   return 0;
}

int MMA8452::readYCount(int *y) {
   char buf[2];
   if(readYRaw((char*)&buf)) {
       return 1;
   }
   if(_bitDepth==BIT_DEPTH_12) {
     *y = twelveBitToSigned(&buf[0]);
   } else {
     *y = eightBitToSigned(&buf[0]);
   }
   return 0;
}

int MMA8452::readZCount(int *z) {
   char buf[2];
   if(readZRaw((char*)&buf)) {
       return 1;
   }
   if(_bitDepth==BIT_DEPTH_12) {
     *z = twelveBitToSigned(&buf[0]);
   } else {
     *z = eightBitToSigned(&buf[0]);
   }
   return 0;
}

double MMA8452::convertCountToGravity(int count, int countsPerG) {
   return (double)count/(double)countsPerG;
}

int MMA8452::getCountsPerG() {
 // assume starting with DYNAMIC_RANGE_2G and BIT_DEPTH_12
   int countsPerG = 1024;
   if(_bitDepth==BIT_DEPTH_8) {
      countsPerG = 64;
   }
   switch(_dynamicRange) {
      case DYNAMIC_RANGE_4G:
         countsPerG /= 2;
      break;
      case DYNAMIC_RANGE_8G:
         countsPerG /= 4;
      break;
   }
   return countsPerG;
}

int MMA8452::readXYZGravity(double *x, double *y, double *z) {
   int xCount = 0, yCount = 0, zCount = 0;
   if(readXYZCounts(&xCount,&yCount,&zCount)) {
      return 1;
   }
   int countsPerG = getCountsPerG();
   
   *x = convertCountToGravity(xCount,countsPerG);
   *y = convertCountToGravity(yCount,countsPerG);
   *z = convertCountToGravity(zCount,countsPerG);
   return 0;
}

int MMA8452::readXGravity(double *x) {
   int xCount = 0;
   if(readXCount(&xCount)) {
      return 1;
   }
   int countsPerG = getCountsPerG();
   
   *x = convertCountToGravity(xCount,countsPerG);
   return 0;
}

int MMA8452::readYGravity(double *y) {
   int yCount = 0;
   if(readYCount(&yCount)) {
      return 1;
   }
   int countsPerG = getCountsPerG();
   
   *y = convertCountToGravity(yCount,countsPerG);
   return 0;
}

int MMA8452::readZGravity(double *z) {
   int zCount = 0;
   if(readZCount(&zCount)) {
      return 1;
   }
   int countsPerG = getCountsPerG();
   
   *z = convertCountToGravity(zCount,countsPerG);
   return 0;
}

// apply an AND mask to a register. read register value, apply mask, write it back
int MMA8452::logicalANDRegister(char addr, char mask) {
   char value = 0;
   // read register value
   if(readRegister(addr,&value)) {
      return 0;
   }
   // apply mask
   value &= mask;
   return writeRegister(addr,value);
}


// apply an OR mask to a register. read register value, apply mask, write it back
int MMA8452::logicalORRegister(char addr, char mask) {
   char value = 0;
   // read register value
   if(readRegister(addr,&value)) {
      return 0;
   }
   // apply mask
   value |= mask;
   return writeRegister(addr,value);
}

// apply an OR mask to a register. read register value, apply mask, write it back
int MMA8452::logicalXORRegister(char addr, char mask) {
   char value = 0;
   // read register value
   if(readRegister(addr,&value)) {
      return 0;
   }
   // apply mask
   value ^= mask;
   return writeRegister(addr,value);
}

// Write register (The device must be placed in Standby Mode to change the value of the registers) 
int MMA8452::writeRegister(char addr, char data) {
    // what this actually does is the following
    // 1. tell I2C bus to start transaction
    // 2. tell slave we want to write (slave address & write flag)
    // 3. send the write address
    // 4. send the data to write
    // 5. tell I2C bus to end transaction

    // we can wrap this up in the I2C library write function
    char buf[2] = {0,0};
    buf[0] = addr;
    buf[1] = data;
    return _i2c.write(MMA8452_ADDRESS, buf,2);
    // note, could also do return writeRegister(addr,&data,1);
}

int MMA8452::eightBitToSigned(char *buf) {
   return (int8_t)*buf;
}

int MMA8452::twelveBitToSigned(char *buf) {
   // cheat by using the int16_t internal type
   // all we need to do is convert to little-endian format and shift right
   int16_t x = 0;
   ((char*)&x)[1] = buf[0];
   ((char*)&x)[0] = buf[1];
   // note this only works because the below is an arithmetic right shift
   return x>>4; 
}

int MMA8452::writeRegister(char addr, char *data, int nbytes) {
    // writing multiple bytes is a little bit annoying because
    // the I2C library doesn't support sending the address separately
    // so we just do it manually
    
    // 1. tell I2C bus to start transaction
    _i2c.start();
    // 2. tell slave we want to write (slave address & write flag)
    if(_i2c.write(_writeAddress)!=1) {
       return 1;
    }
    // 3. send the write address
    if(_i2c.write(addr)!=1) {
       return 1;
    }
    // 4. send the data to write
    for(int i=0; i<nbytes; i++) {
       if(_i2c.write(data[i])!=1) {
          return 1;
       }
    }
    // 5. tell I2C bus to end transaction
    _i2c.stop();
    return 0;
}

int MMA8452::readRegister(char addr, char *dst, int nbytes) {
    // this is a bit odd, but basically proceeds like this
    // 1. Send a start command
    // 2. Tell the slave we want to write (slave address & write flag)
    // 3. Send the address of the register (addr)
    // 4. Send another start command to delineate read portion
    // 5. Tell the slave we want to read (slave address & read flag)
    // 6. Read the register value bytes
    // 7. Send a stop command
    
    // we can wrap this process in the I2C library read and write commands
    if(_i2c.write(MMA8452_ADDRESS,&addr,1,true)) {
       return 1;
    }
    return _i2c.read(MMA8452_ADDRESS,dst,nbytes);
}

// most registers are 1 byte, so here is a convenience function
int MMA8452::readRegister(char addr, char *dst) {
    return readRegister(addr,dst,1);
}

MMA8452::BitDepth MMA8452::getBitDepth() {
   return _bitDepth;
}

#ifdef MMA8452_DEBUG
void MMA8452::debugRegister(char reg) {
   // get register value
   char v = 0;
   if(readRegister(reg,&v)) {
      MMA8452_DBG("Error reading specified register");
      return;
   }
   // print out details
   switch(reg) {
      case MMA8452_CTRL_REG_1:
         MMA8452_DBG("CTRL_REG_1 has value: 0x%x",v);
         MMA8452_DBG(" 7  ALSP_RATE_1: %d",(v&0x80)>>7);
         MMA8452_DBG(" 6  ALSP_RATE_0: %d",(v&0x40)>>6);
         MMA8452_DBG(" 5  DR2: %d",        (v&0x20)>>5);
         MMA8452_DBG(" 4  DR1: %d",        (v&0x10)>>4);
         MMA8452_DBG(" 3  DR0: %d",        (v&0x08)>>3);
         MMA8452_DBG(" 2  LNOISE: %d",     (v&0x04)>>2);
         MMA8452_DBG(" 1  FREAD: %d",      (v&0x02)>>1);
         MMA8452_DBG(" 0  ACTIVE: %d",     (v&0x01));
      break;
        
      case MMA8452_XYZ_DATA_CFG:
         MMA8452_DBG("XYZ_DATA_CFG has value: 0x%x",v);
         MMA8452_DBG(" 7  Unused: %d", (v&0x80)>>7);
         MMA8452_DBG(" 6  0: %d",      (v&0x40)>>6);
         MMA8452_DBG(" 5  0: %d",      (v&0x20)>>5);
         MMA8452_DBG(" 4  HPF_Out: %d",(v&0x10)>>4);
         MMA8452_DBG(" 3  0: %d",      (v&0x08)>>3);
         MMA8452_DBG(" 2  0: %d",      (v&0x04)>>2);
         MMA8452_DBG(" 1  FS1: %d",    (v&0x02)>>1);
         MMA8452_DBG(" 0  FS0: %d",    (v&0x01));
         switch(v&0x03) {
            case 0:
               MMA8452_DBG("Dynamic range: 2G");
            break;
            case 1:
               MMA8452_DBG("Dynamic range: 4G");
            break;
            case 2:
               MMA8452_DBG("Dynamic range: 8G");
            break;
            default:
               MMA8452_DBG("Unknown dynamic range");
            break;
         }
      break;
      
      case MMA8452_STATUS:
         MMA8452_DBG("STATUS has value: 0x%x",v);
         MMA8452_DBG(" 7  ZYXOW: %d",(v&0x80)>>7);
         MMA8452_DBG(" 6  ZOW: %d",  (v&0x40)>>6);
         MMA8452_DBG(" 5  YOW: %d",  (v&0x20)>>5);
         MMA8452_DBG(" 4  XOW: %d",  (v&0x10)>>4);
         MMA8452_DBG(" 3  ZYXDR: %d",(v&0x08)>>3);
         MMA8452_DBG(" 2  ZDR: %d",  (v&0x04)>>2);
         MMA8452_DBG(" 1  YDR: %d",  (v&0x02)>>1);
         MMA8452_DBG(" 0  XDR: %d",  (v&0x01));
      break;
      
      default:
         MMA8452_DBG("Unknown register address: 0x%x",reg);
      break;
   }
}
#endif