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.

Revision:
12:172540ff6b8b
Parent:
11:dfd1e0afcb7b
Child:
13:4bd8b4cd479d
diff -r dfd1e0afcb7b -r 172540ff6b8b MMA8452.cpp
--- a/MMA8452.cpp	Tue Mar 04 16:23:40 2014 +0000
+++ b/MMA8452.cpp	Tue Mar 04 17:50:47 2014 +0000
@@ -25,11 +25,17 @@
 // 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) {
    DBG("Creating MMA8452");
+   
+   // set I2C frequency
    _i2c.frequency(_frequency);
    
-   // setup read and write addresses to avoid duplication
+   // 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);
    DBG("Done");
 }
 
@@ -40,13 +46,13 @@
 // Setting the control register bit 1 to true to activate the MMA8452
 int MMA8452::activate() {
     // perform write and return error code
-    return logicalORRegister(CTRL_REG_1,MMA8452_ACTIVE_MASK);
+    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(CTRL_REG_1,MMA8452_STANDBY_MASK);
+    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,
@@ -102,6 +108,7 @@
 }
 
 int MMA8452::setBitDepth(BitDepth depth,int toggleActivation) {
+   _bitDepth = depth;
    return maskAndApplyRegister(
       MMA8452_CTRL_REG_1,
       MMA8452_BIT_DEPTH_MASK,
@@ -110,105 +117,25 @@
    );
 }
 
-
-// Get device ID 
-int MMA8452::getDeviceID(char *dst)
-{
-    return readRegister(WHO_AM_I,dst);
+int MMA8452::isXYZReady() {
+   char rval = 0;
+   if(readRegister(MMA8452_STATUS,&rval)) {
+      return 0;
+   }
+   return (rval&MMA8452_STATUS_ZYXDR_MASK);
 }
-
-
-int MMA8452::readRaw(char src, char *dst, int len) {
-    // this is the register we want to get data from               
-    char register_address[1];
-    register_address[0] = src;
-    
-    if(_i2c.write(_writeAddress,register_address,1,true) == 0)
-    {
-        if(_i2c.read(_readAddress,dst,len)==0)
-        {
-           return 0;
-        }
-    }
-    
-    // failure case, zero array and return error
-    for(int i=0; i<len; i++) {
-       dst[i] = 0x00;
-    }
-    return 1;   
-}
-
-// Reads x data. This method reads two registers containing the x-axis values from the accelerometer. 
-// It takes a 2 byte char array and copies the register values into the buffer. If it fails the char array
-// is set to '0'. It returns '0' success '1' fail. This method does nothing to the registers - just returns
-// the raw data.
-//int MMA8452::read_x(int& xaxisLSB)
-int MMA8452::readRawX(char *xaxis) {   
-    return readRaw(OUT_X_MSB,xaxis,2);  
-}
-
-
-// Reads y data. This method reads two registers containing the x-axis values from the accelerometer. 
-// It takes a 2 byte char array and copies the register values into the buffer. If it fails the char array
-// is set to '0'. It returns '0' success '1' fail. This method does nothing to the registers - just returns
-// the raw data.
-
-int MMA8452::readRawY(char *yaxis) {
-   return readRaw(OUT_Y_MSB,yaxis,2);
+ 
+int MMA8452::getDeviceID(char *dst) {
+   return readRegister(MMA8452_WHO_AM_I,dst);
 }
 
-
-
-// Reads z data. This method reads two registers containing the x-axis values from the accelerometer. 
-// It takes a 2 byte char array and copies the register values into the buffer. If it fails the char array
-// is set to '0'. It returns '0' success '1' fail. This method does nothing to the registers - just returns
-// the raw data.
-
-int MMA8452::readRawZ(char *zaxis)
-{
-   return readRaw(OUT_Z_MSB,zaxis,2);
+int MMA8452::getStatus(char* dst) {
+   return readRegister(MMA8452_STATUS,dst);
 }
 
-
-
-// Reads y data
-int MMA8452::read_y()
-{
-    char mcu_address = (MMA8452_ADDRESS <<1);
-
-    _i2c.start();                  // Start
-    _i2c.write(mcu_address);              // A write to device 0x98
-    _i2c.write(OUT_Y_MSB);             // Register to read
-    _i2c.start();                  
-    _i2c.write(mcu_address);              // Read from device 0x99
-    int y = _i2c.read(0);         // Read the data
-    _i2c.stop();
-    
-    return y; 
-
-}
-
-// Reads z data
-int MMA8452::read_z()
-{
-    char mcu_address = (MMA8452_ADDRESS <<1);
-    
-    _i2c.start();                  // Start
-    _i2c.write(mcu_address);              // A write to device 0x98
-    _i2c.write(OUT_Z_MSB);             // Register to read
-    _i2c.start();                  
-    _i2c.write(mcu_address);              // Read from device 0x99
-    int z = _i2c.read(0);         // Read the data
-    _i2c.stop();
-    
-    return z;
-
-}
-
-
 MMA8452::DynamicRange MMA8452::getDynamicRange() {
    char rval = 0;
-   if(readRegister(MMA8452_CTRL_REG_1,&rval)) {
+   if(readRegister(MMA8452_XYZ_DATA_CFG,&rval)) {
       return MMA8452::DYNAMIC_RANGE_UNKNOWN;
    }
    rval &= (MMA8452_DYNAMIC_RANGE_MASK^0xFF);
@@ -228,35 +155,15 @@
 }
 
 // Reads xyz
-int MMA8452::readRawXYZ(char *x, char *y, char *z) 
-{
-    
-    
-    char mcu_address = (MMA8452_ADDRESS <<1);
-    char register_buffer[6] ={0,0,0,0,0,0};
-    const char Addr_X = OUT_X_MSB;
-    _i2c.write(mcu_address);              // A write to device 0x98
-    _i2c.write(MMA8452_ADDRESS, &Addr_X, 1);         // Pointer to the OUT_X_MSB register
-    
-    if(_i2c.write(mcu_address,&Addr_X,1) == 0)
-    {
-        if(_i2c.read(mcu_address,register_buffer,6) == 0)
-        {
-            *x = register_buffer[1];
-            *y = register_buffer[3];
-            *z = register_buffer[5];
-            return 0;           // yahoooooo
-        }
-        else
-        {
-            return 1;           // failed oh nooo!
-        }    
-    }
-    else
-    {
-        return 1;               // failed oh nooo!
-    }
-
+int MMA8452::readRawXYZ(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);
 }
 
 // apply an AND mask to a register. read register value, apply mask, write it back
@@ -284,7 +191,6 @@
    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;
@@ -367,7 +273,7 @@
    // get register value
    char v = 0;
    if(readRegister(reg,&v)) {
-      DBG("Error reading control register");
+      DBG("Error reading specified register");
       return;
    }
    // print out details
@@ -410,6 +316,18 @@
          }
       break;
       
+      case MMA8452_STATUS:
+         DBG("STATUS has value: 0x%x",v);
+         DBG(" 7  ZYXOW: %d",(v&0x80)>>7);
+         DBG(" 6  ZOW: %d",  (v&0x40)>>6);
+         DBG(" 5  YOW: %d",  (v&0x20)>>5);
+         DBG(" 4  XOW: %d",  (v&0x10)>>4);
+         DBG(" 3  ZYXDR: %d",(v&0x08)>>3);
+         DBG(" 2  ZDR: %d",  (v&0x04)>>2);
+         DBG(" 1  YDR: %d",  (v&0x02)>>1);
+         DBG(" 0  XDR: %d",  (v&0x01));
+      break;
+      
       default:
          DBG("Unknown register address: 0x%x",reg);
       break;