microbit-dal/source/MicroBitAccelerometer.cpp

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/**
* Class definition for MicroBit Accelerometer.
*
* Represents an implementation of the Freescale MMA8653 3 axis accelerometer
* Also includes basic data caching and on demand activation.
*/
#include "MicroBit.h"
/**
* Configures the accelerometer for G range and sample rate defined
* in this object. The nearest values are chosen to those defined
* that are supported by the hardware. The instance variables are then
* updated to reflect reality.
*/
void MicroBitAccelerometer::configure()
{
const MMA8653SampleRangeConfig *actualSampleRange;
const MMA8653SampleRateConfig *actualSampleRate;
// First find the nearest sample rate to that specified.
actualSampleRate = &MMA8653SampleRate[MMA8653_SAMPLE_RATES-1];
for (int i=MMA8653_SAMPLE_RATES-1; i>=0; i--)
{
if(MMA8653SampleRate[i].sample_period < this->samplePeriod * 1000)
break;
actualSampleRate = &MMA8653SampleRate[i];
}
// Now find the nearest sample range to that specified.
actualSampleRange = &MMA8653SampleRange[MMA8653_SAMPLE_RANGES-1];
for (int i=MMA8653_SAMPLE_RANGES-1; i>=0; i--)
{
if(MMA8653SampleRange[i].sample_range < this->sampleRange)
break;
actualSampleRange = &MMA8653SampleRange[i];
}
// OK, we have the correct data. Update our local state.
this->samplePeriod = actualSampleRate->sample_period / 1000;
this->sampleRange = actualSampleRange->sample_range;
// Now configure the accelerometer accordingly.
// First place the device into standby mode, so it can be configured.
writeCommand(MMA8653_CTRL_REG1, 0x00);
// Enable high precisiosn mode. This consumes a bit more power, but still only 184 uA!
writeCommand(MMA8653_CTRL_REG2, 0x10);
// Enable the INT1 interrupt pin.
writeCommand(MMA8653_CTRL_REG4, 0x01);
// Select the DATA_READY event source to be routed to INT1
writeCommand(MMA8653_CTRL_REG5, 0x01);
// Configure for the selected g range.
writeCommand(MMA8653_XYZ_DATA_CFG, actualSampleRange->xyz_data_cfg);
// Bring the device back online, with 10bit wide samples at the requested frequency.
writeCommand(MMA8653_CTRL_REG1, actualSampleRate->ctrl_reg1 | 0x01);
}
/**
* Issues a standard, 2 byte I2C command write to the accelerometer.
* Blocks the calling thread until complete.
*
* @param reg The address of the register to write to.
* @param value The value to write.
*/
void MicroBitAccelerometer::writeCommand(uint8_t reg, uint8_t value)
{
uint8_t command[2];
command[0] = reg;
command[1] = value;
uBit.i2c.write(address, (const char *)command, 2);
}
/**
* Issues a read command into the specified buffer.
* Blocks the calling thread until complete.
*
* @param reg The address of the register to access.
* @param buffer Memory area to read the data into.
* @param length The number of bytes to read.
*/
void MicroBitAccelerometer::readCommand(uint8_t reg, uint8_t* buffer, int length)
{
uBit.i2c.write(address, (const char *)&reg, 1, true);
uBit.i2c.read(address, (char *)buffer, length);
}
/**
* Constructor.
* Create an accelerometer representation with the given ID.
* @param id the ID of the new object.
* @param address the default base address of the accelerometer.
*
* Example:
* @code
* accelerometer(MICROBIT_ID_ACCELEROMETER, MMA8653_DEFAULT_ADDR)
* @endcode
*/
MicroBitAccelerometer::MicroBitAccelerometer(uint16_t id, uint16_t address) : sample(), int1(MICROBIT_PIN_ACCEL_DATA_READY)
{
// Store our identifiers.
this->id = id;
this->address = address;
// Update our internal state for 50Hz at +/- 2g (50Hz has a period af 20ms).
this->samplePeriod = 20;
this->sampleRange = 2;
// Configure and enable the accelerometer.
this->configure();
// indicate that we're ready to receive tick callbacks.
uBit.flags |= MICROBIT_FLAG_ACCELEROMETER_RUNNING;
}
/**
* Attempts to determine the 8 bit ID from the accelerometer.
* @return the 8 bit ID returned by the accelerometer
*
* Example:
* @code
* uBit.accelerometer.whoAmI();
* @endcode
*/
int MicroBitAccelerometer::whoAmI()
{
uint8_t data;
readCommand(MMA8653_WHOAMI, &data, 1);
return (int)data;
}
/**
* Reads the acceleration data from the accelerometer, and stores it in our buffer.
* This is called by the tick() member function, if the interrupt is set!
*/
void MicroBitAccelerometer::update()
{
int8_t data[6];
static int count=0;
readCommand(MMA8653_OUT_X_MSB, (uint8_t *)data, 6);
// read MSB values...
sample.x = data[0];
sample.y = data[2];
sample.z = data[4];
// Normalize the data in the 0..1024 range.
sample.x *= 8;
sample.y *= 8;
sample.z *= 8;
// Invert the x and y axes, so that the reference frame aligns with micro:bit expectations
sample.x = -sample.x;
sample.y = -sample.y;
#if CONFIG_ENABLED(USE_ACCEL_LSB)
// Add in LSB values.
sample.x += (data[1] / 64);
sample.y += (data[3] / 64);
sample.z += (data[5] / 64);
#endif
// Scale into millig (approx!)
sample.x *= this->sampleRange;
sample.y *= this->sampleRange;
sample.z *= this->sampleRange;
//TODO: Issue an event.
};
/**
* Attempts to set the sample rate of the accelerometer to the specified value (in ms).
* n.b. the requested rate may not be possible on the hardware. In this case, the
* nearest lower rate is chosen.
* @param period the requested time between samples, in milliseconds.
*/
void MicroBitAccelerometer::setPeriod(int period)
{
this->samplePeriod = period;
this->configure();
}
/**
* Reads the currently configured sample rate of the accelerometer.
* @return The time between samples, in milliseconds.
*/
int MicroBitAccelerometer::getPeriod()
{
return (int)samplePeriod;
}
/**
* Attempts to set the sample range of the accelerometer to the specified value (in g).
* n.b. the requested range may not be possible on the hardware. In this case, the
* nearest lower rate is chosen.
* @param range The requested sample range of samples, in g.
*/
void MicroBitAccelerometer::setRange(int range)
{
this->sampleRange = range;
this->configure();
}
/**
* Reads the currently configured sample range of the accelerometer.
* @return The sample range, in g.
*/
int MicroBitAccelerometer::getRange()
{
return (int)sampleRange;
}
/**
* Reads the X axis value of the latest update from the accelerometer.
* Currently limited to +/- 2g
* @return The force measured in the X axis, in milli-g.
*
* Example:
* @code
* uBit.accelerometer.getX();
* @endcode
*/
int MicroBitAccelerometer::getX()
{
return sample.x;
}
/**
* Reads the Y axis value of the latest update from the accelerometer.
* Currently limited to +/- 2g
* @return The force measured in the Y axis, in milli-g.
*
* Example:
* @code
* uBit.accelerometer.getY();
* @endcode
*/
int MicroBitAccelerometer::getY()
{
return sample.y;
}
/**
* Reads the Z axis value of the latest update from the accelerometer.
* Currently limited to +/- 2g
* @return The force measured in the Z axis, in milli-g.
*
* Example:
* @code
* uBit.accelerometer.getZ();
* @endcode
*/
int MicroBitAccelerometer::getZ()
{
return sample.z;
}
/**
* periodic callback from MicroBit clock.
* Check if any data is ready for reading by checking the interrupt flag on the accelerometer
*/
void MicroBitAccelerometer::idleTick()
{
// Poll interrupt line from accelerometer.
// n.b. Default is Active LO. Interrupt is cleared in data read.
//
if(!int1)
update();
}
/**
* Returns 0 or 1. 1 indicates data is waiting to be read, zero means data is not ready to be read.
*/
int MicroBitAccelerometer::isIdleCallbackNeeded()
{
return !int1;
}
const MMA8653SampleRangeConfig MMA8653SampleRange[MMA8653_SAMPLE_RANGES] = {
{2, 0},
{4, 1},
{8, 2}
};
const MMA8653SampleRateConfig MMA8653SampleRate[MMA8653_SAMPLE_RATES] = {
{1250, 0x00},
{2500, 0x08},
{5000, 0x10},
{10000, 0x18},
{20000, 0x20},
{80000, 0x28},
{160000, 0x30},
{640000, 0x38}
};