Ashley Mills / MMA8452

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.

Diff: MMA8452.cpp

Revision:
8:89272163f395
Parent:
7:8aa5123d403f
Parent:
6:f6bde04bf8be
Child:
9:dfb0f6a7a455
--- a/MMA8452.cpp	Thu Oct 17 09:40:10 2013 +0000
+++ b/MMA8452.cpp	Thu Oct 17 10:08:51 2013 +0000
@@ -19,20 +19,19 @@
 
 # include "MMA8452.h"
 
-
-
-
-
-
 // Connect module at I2C address using I2C port pins sda and scl
 Accelerometer_MMA8452::Accelerometer_MMA8452(PinName sda, PinName scl,int frequency) : m_i2c(sda, scl) , m_frequency(frequency)
 {
     //m_i2c.frequency(m_frequency);
+    
+    // setup read and write addresses to avoid duplication
+   _readAddress   = (MMA8452_ADDRESS<<1) | 0x01;
+   _writeAddress  = (MMA8452_ADDRESS<<1) & 0xFE;
 }
 
 
 // Destroys instance
-Accelerometer_MMA8452::~Accelerometer_MMA8452()
+Accelerometer_MMA8452::~Accelerometer_MMA8452() 
 {
 
 }
@@ -40,75 +39,46 @@
 // Setting the control register bit 1 to true to activate the MMA8452
 int Accelerometer_MMA8452::activate()
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
-    char init[2];
-    init[0] = CTRL_REG_1;                 // control register 1
-    init[1] = ACTIVE;                     // set to active
+    // set control register 1 to active
+    char init[2] = {CTRL_REG_1,ACTIVE};
     
-    if(m_i2c.write(mcu_address,init,2) == 0)
-    {
-         return 0;  // return 0 to indicate success
-    }
-    else
-    {
-        return 1;   // crumbs it failed!!!
-    }
-         
+    // perform write and return error code
+    return m_i2c.write(_writeAddress,init,2);
 }
 
 
 // Get 'Fast Read Mode' called F_READ. If bit 1 is set '1' then F_READ is active. Fast read will skip LSB when reading xyz
 // resisters from 0x01 to 0x06. When F_READ is '0' then all 6 registers will be read.
 
-int Accelerometer_MMA8452::get_CTRL_Reg1(int& CTRL_Reg)
-{
+int Accelerometer_MMA8452::get_CTRL_Reg1(int* CTRL_Reg)
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
     m_i2c.start();
-    if( m_i2c.write( mcu_address & 0xFE) == 0)          // just good practice to force bit 1 to a '0' by ANDing with 0xFE
+    if( m_i2c.write(_writeAddress) == 0)
     {
-        return 1;                                       // we failed to write the mcu address on the bus to initiate dialogue 
+        return 1;                                   // we failed to write the mcu address on the bus to initiate dialogue 
     }
     if( m_i2c.write( CTRL_REG_1) == 0) 
     {
         return 1;                                       // we failed to write 'status' to the chip
     }
     m_i2c.start();
-    if( m_i2c.write( mcu_address | 0x01) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
+    if( m_i2c.write(_readAddress) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
     {
         return 1;                                       // we failed to request a read from that mcu - this really is just writing the mcu vaule on the bus
     }
-    CTRL_Reg  = m_i2c.read(0);
+    *CTRL_Reg  = m_i2c.read(0);
     m_i2c.stop();
     return 0;
-    
-
-}
-
-
-
-
 }
 
 // Setting the control register bit 1 to true to activate the MMA8452
 int Accelerometer_MMA8452::standby()
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
-    char init[2];
-    init[0] = CTRL_REG_1;                 // control register 1
-    init[1] = STANDBY;                    // set to standby
+    // set control register 1 to standby
+    char init[2] = {CTRL_REG_1,STANDBY};
     
-    if(m_i2c.write(mcu_address,init,2) == 0)
-    {
-         // pc.printf("The initialisation worked");
-         return 0;  // return 0 to indicate success
-    }
-    else
-    {
-        // pc.printf("The initialisation failed");
-        return 1;   // crumbs it failed!!!
-    }
-         
+    // write to the register and return the error code
+    return m_i2c.write(_writeAddress,init,2);
 }
 
 
@@ -126,9 +96,8 @@
 // Get real time status of device - it can be STANDBY, WAKE or SLEEP
 int Accelerometer_MMA8452::get_SystemMode(int& deviceSystemMode)
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
     m_i2c.start();
-    if( m_i2c.write( mcu_address & 0xFE) == 0)          // just good practice to force bit 1 to a '0' by ANDing with 0xFE
+    if( m_i2c.write(_writeAddress) == 0)        
     {
         return 1;                                       // we failed to write the mcu address on the bus to initiate dialogue 
     }
@@ -137,7 +106,7 @@
         return 1;                                       // we failed to write 'status' to the chip
     }
     m_i2c.start();
-    if( m_i2c.write( mcu_address | 0x01) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
+    if( m_i2c.write(_readAddress) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
     {
         return 1;                                       // we failed to request a read from that mcu - this really is just writing the mcu vaule on the bus
     }
@@ -153,18 +122,17 @@
 // Get real time status of device - it can be STANDBY, WAKE or SLEEP
 int Accelerometer_MMA8452::get_Status(int& deviceStatus)
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
     m_i2c.start();
-    if( m_i2c.write( mcu_address & 0xFE) == 0)          // just good practice to force bit 1 to a '0' by ANDing with 0xFE
+    if( m_i2c.write(_writeAddress) == 0) // tell the bus this is a write
     {
         return 1;                                       // we failed to write the mcu address on the bus to initiate dialogue 
     }
-    if( m_i2c.write( STATUS) == 0) 
+    if( m_i2c.write(STATUS) == 0)
     {
         return 1;                                       // we failed to write 'status' to the chip
     }
     m_i2c.start();
-    if( m_i2c.write( mcu_address | 0x01) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
+    if( m_i2c.write(_readAddress) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
     {
         return 1;                                       // we failed to request a read from that mcu - this really is just writing the mcu vaule on the bus
     }
@@ -179,9 +147,8 @@
 // Get device ID 
 int Accelerometer_MMA8452::get_DeviceID(int& deviceID)
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);
     m_i2c.start();
-    if( m_i2c.write( mcu_address & 0xFE) == 0)          // just good practice to force bit 1 to a '0' by ANDing with 0xFE
+    if( m_i2c.write(_writeAddress) == 0)          // just good practice to force bit 1 to a '0' by ANDing with 0xFE
     {
         return 1;                                       // we failed to write the mcu address on the bus to initiate dialogue 
     }
@@ -190,7 +157,7 @@
         return 1;                                       // we failed to write 'who am i' to the chip
     }
     m_i2c.start();
-    if( m_i2c.write( mcu_address | 0x01) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
+    if( m_i2c.write(_readAddress) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
     {
         return 1;                                       // we failed to request a read from that mcu - this really is just writing the mcu vaule on the bus
     }
@@ -226,6 +193,25 @@
 }
 */
 
+int Accelerometer_MMA8452::read_raw(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(m_i2c.write(_writeAddress,register_address,1,true) == 0)
+    {
+        if(m_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
@@ -233,37 +219,23 @@
 // the raw data.
 //int Accelerometer_MMA8452::read_x(int& xaxisLSB)
 int Accelerometer_MMA8452::read_x_raw(char *xaxis)
-{
-    char mcu_address = (MMA8452_ADDRESS<<1);                // this is the slave address on the bus we want data from
-    char xaxis_buffer[2];                                   // this will contain data from that register
-    char xaxis_register[1];                     
-    xaxis_register[0] = OUT_X_MSB;                          // this is the register we want to get data from
+{   
+    // this is the register we want to get data from               
+    char xaxis_register[1] = {OUT_X_MSB};
     //signed short s = 0;
     
-    if(m_i2c.write(mcu_address,xaxis_register,1,true) == 0)
+    if(m_i2c.write(_writeAddress,xaxis_register,1,true) == 0)
     {
-        if(m_i2c.read(mcu_address,xaxis_buffer,2) == 0)
+        if(m_i2c.read(_readAddress,xaxis,2)==0)
         {
-            //strcpy(xaxis, xaxis_buffer);
-            memcpy(xaxis, xaxis_buffer, 2);
-            //xaxis[0] = 0x00;                        // make sure the array is set to zero
-            //xaxis[1] = 0x00;
-            //s = *reinterpret_cast<short*>(&xaxis);
-            return 0;                               // great we got the two octets
-        }
-        else
-        {
-            xaxis[0] = 0x00;                        // make sure the array is set to zero
-            xaxis[1] = 0x00;
-            return 1;                               // failed to read the 12 bit x value
+           return 0;
         }
     }
-    else
-    {
-        xaxis[0] = 0x00;                            // make sure the array is set to zero
-        xaxis[1] = 0x00;
-        return 1;                                   // failed to write and request the OUT_X_MSB bit
-    }    
+    
+    // failure case
+    xaxis[0] = 0x00;                            // make sure the array is set to zero
+    xaxis[1] = 0x00;
+    return 1;                                   // failed to write and request the OUT_X_MSB bit    
 }
 
 
@@ -272,38 +244,8 @@
 // is set to '0'. It returns '0' success '1' fail. This method does nothing to the registers - just returns
 // the raw data.
 
-int Accelerometer_MMA8452::read_y_raw(char *yaxis)
-{
-    char mcu_address = (MMA8452_ADDRESS<<1);                // this is the slave address on the bus we want data from
-    char yaxis_buffer[2];                                   // this will contain data from that register
-    char yaxis_register[1];                     
-    yaxis_register[0] = OUT_Y_MSB;                          // this is the register we want to get data from
-    //signed short s = 0;
-    
-    if(m_i2c.write(mcu_address,yaxis_register,1,true) == 0)
-    {
-        if(m_i2c.read(mcu_address,yaxis_buffer,2) == 0)
-        {
-            //strcpy(yaxis, yaxis_buffer);
-            memcpy(yaxis, yaxis_buffer, 2);
-            //yaxis[0] = 0x00;                        // make sure the array is set to zero
-            //yaxis[1] = 0x00;
-            //s = *reinterpret_cast<short*>(&xaxis);
-            return 0;                               // great we got the two octets
-        }
-        else
-        {
-            yaxis[0] = 0x00;                        // make sure the array is set to zero
-            yaxis[1] = 0x00;
-            return 1;                               // failed to read the 12 bit y value
-        }
-    }
-    else
-    {
-        yaxis[0] = 0x00;                            // make sure the array is set to zero
-        yaxis[1] = 0x00;
-        return 1;                                   // failed to write and request the OUT_Y_MSB bit
-    }    
+int Accelerometer_MMA8452::read_y_raw(char *yaxis) {
+   return read_raw(OUT_Y_MSB,yaxis,2);
 }
 
 
@@ -315,37 +257,7 @@
 
 int Accelerometer_MMA8452::read_z_raw(char *zaxis)
 {
-    char mcu_address = (MMA8452_ADDRESS<<1);                // this is the slave address on the bus we want data from
-    char zaxis_buffer[2];                                   // this will contain data from that register
-    char zaxis_register[1];                     
-    zaxis_register[0] = OUT_Z_MSB;                          // this is the register we want to get data from
-    //signed short s = 0;
-    
-    if(m_i2c.write(mcu_address,zaxis_register,1,true) == 0)
-    {
-        //if(m_i2c.read(mcu_address,zaxis_buffer,2) == 0)
-        if(m_i2c.read(mcu_address,zaxis,2) == 0)
-        {
-            //strcpy(yaxis, yaxis_buffer);
-            //memcpy(zaxis, zaxis_buffer, 2);
-            //yaxis[0] = 0x00;                        // make sure the array is set to zero
-            //yaxis[1] = 0x00;
-            //s = *reinterpret_cast<short*>(&xaxis);
-            return 0;                               // great we got the two octets
-        }
-        else
-        {
-            zaxis[0] = 0x00;                        // make sure the array is set to zero
-            zaxis[1] = 0x00;
-            return 1;                               // failed to read the 12 bit y value
-        }
-    }
-    else
-    {
-        zaxis[0] = 0x00;                            // make sure the array is set to zero
-        zaxis[1] = 0x00;
-        return 1;                                   // failed to write and request the OUT_Y_MSB bit
-    }    
+   return read_raw(OUT_Z_MSB,zaxis,2);
 }
 
 
@@ -444,13 +356,22 @@
 char Accelerometer_MMA8452::read_reg(char addr)
 {
     
-    m_i2c.start();                  // Start
-    m_i2c.write(0x98);              // A write to device 0x98
-    m_i2c.write(addr);              // Register to read
-    m_i2c.start();                  
-    m_i2c.write(0x99);              // Read from device 0x99
-    char c = m_i2c.read(0);         // Read the data
-    m_i2c.stop();                   
+    m_i2c.start();
+    if( m_i2c.write(_writeAddress) == 0)
+    {
+        return 1;                                   // we failed to write the mcu address on the bus to initiate dialogue 
+    }
+    if( m_i2c.write( addr) == 0) 
+    {
+        return 1;                                       // we failed to write 'status' to the chip
+    }
+    m_i2c.start();
+    if( m_i2c.write(_readAddress) == 0)          // this is asking to read the slave mcu address - even though it's a 'write' method!!! Crap API...
+    {
+        return 1;                                       // we failed to request a read from that mcu - this really is just writing the mcu vaule on the bus
+    }
+    char c  = m_i2c.read(0);
+    m_i2c.stop();      
  
     return c;