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:
- 2014-03-04
- Revision:
- 12:172540ff6b8b
- Parent:
- 11:dfd1e0afcb7b
- Child:
- 13:4bd8b4cd479d
File content as of revision 12:172540ff6b8b:
// Author: Nicholas Herriot, Ashley Mills /* 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" extern Serial pc; // 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 for convenience _readAddress = MMA8452_ADDRESS | 0x01; _writeAddress = MMA8452_ADDRESS & 0xFE; // set some defaults _bitDepth = BIT_DEPTH_UNKNOWN; setBitDepth(BIT_DEPTH_12); 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) { 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 ); } int MMA8452::isXYZReady() { char rval = 0; if(readRegister(MMA8452_STATUS,&rval)) { return 0; } return (rval&MMA8452_STATUS_ZYXDR_MASK); } 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::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 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::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); } void MMA8452::debugRegister(char reg) { // get register value char v = 0; if(readRegister(reg,&v)) { DBG("Error reading specified register"); return; } // print out details switch(reg) { case MMA8452_CTRL_REG_1: DBG("CTRL_REG_1 has value: 0x%x",v); DBG(" 7 ALSP_RATE_1: %d",(v&0x80)>>7); DBG(" 6 ALSP_RATE_0: %d",(v&0x40)>>6); DBG(" 5 DR2: %d", (v&0x20)>>5); DBG(" 4 DR1: %d", (v&0x10)>>4); DBG(" 3 DR0: %d", (v&0x08)>>3); DBG(" 2 LNOISE: %d", (v&0x04)>>2); DBG(" 1 FREAD: %d", (v&0x02)>>1); DBG(" 0 ACTIVE: %d", (v&0x01)); break; case MMA8452_XYZ_DATA_CFG: DBG("XYZ_DATA_CFG has value: 0x%x",v); DBG(" 7 Unused: %d", (v&0x80)>>7); DBG(" 6 0: %d", (v&0x40)>>6); DBG(" 5 0: %d", (v&0x20)>>5); DBG(" 4 HPF_Out: %d",(v&0x10)>>4); DBG(" 3 0: %d", (v&0x08)>>3); DBG(" 2 0: %d", (v&0x04)>>2); DBG(" 1 FS1: %d", (v&0x02)>>1); DBG(" 0 FS0: %d", (v&0x01)); switch(v&0x03) { case 0: DBG("Dynamic range: 2G"); break; case 1: DBG("Dynamic range: 4G"); break; case 2: DBG("Dynamic range: 8G"); break; default: DBG("Unknown dynamic range"); break; } 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; } }