hal/lib/Athena/Accelerometer.cpp

#include "HAL/Accelerometer.hpp"

#include "ChipObject.h"
#include <stdint.h>
#include <stdio.h>
#include <assert.h>

// The 7-bit I2C address with a 0 "send" bit
static const uint8_t kSendAddress = (0x1c << 1) | 0;

// The 7-bit I2C address with a 1 "receive" bit
static const uint8_t kReceiveAddress = (0x1c << 1) | 1;

static const uint8_t kControlTxRx = 1;
static const uint8_t kControlStart = 2;
static const uint8_t kControlStop = 4;

static tAccel *accel = 0;
static AccelerometerRange accelerometerRange;

// Register addresses
enum Register {
	kReg_Status = 0x00,
	kReg_OutXMSB = 0x01,
	kReg_OutXLSB = 0x02,
	kReg_OutYMSB = 0x03,
	kReg_OutYLSB = 0x04,
	kReg_OutZMSB = 0x05,
	kReg_OutZLSB = 0x06,
	kReg_Sysmod = 0x0B,
	kReg_IntSource = 0x0C,
	kReg_WhoAmI = 0x0D,
	kReg_XYZDataCfg = 0x0E,
	kReg_HPFilterCutoff = 0x0F,
	kReg_PLStatus = 0x10,
	kReg_PLCfg = 0x11,
	kReg_PLCount = 0x12,
	kReg_PLBfZcomp = 0x13,
	kReg_PLThsReg = 0x14,
	kReg_FFMtCfg = 0x15,
	kReg_FFMtSrc = 0x16,
	kReg_FFMtThs = 0x17,
	kReg_FFMtCount = 0x18,
	kReg_TransientCfg = 0x1D,
	kReg_TransientSrc = 0x1E,
	kReg_TransientThs = 0x1F,
	kReg_TransientCount = 0x20,
	kReg_PulseCfg = 0x21,
	kReg_PulseSrc = 0x22,
	kReg_PulseThsx = 0x23,
	kReg_PulseThsy = 0x24,
	kReg_PulseThsz = 0x25,
	kReg_PulseTmlt = 0x26,
	kReg_PulseLtcy = 0x27,
	kReg_PulseWind = 0x28,
	kReg_ASlpCount = 0x29,
	kReg_CtrlReg1 = 0x2A,
	kReg_CtrlReg2 = 0x2B,
	kReg_CtrlReg3 = 0x2C,
	kReg_CtrlReg4 = 0x2D,
	kReg_CtrlReg5 = 0x2E,
	kReg_OffX = 0x2F,
	kReg_OffY = 0x30,
	kReg_OffZ = 0x31
};

extern "C" uint32_t getFPGATime(int32_t *status);

static void writeRegister(Register reg, uint8_t data);
static uint8_t readRegister(Register reg);

/**
 * Initialize the accelerometer.
 */
static void initializeAccelerometer() {
	int32_t status;

	if(!accel) {
		accel = tAccel::create(&status);

		// Enable I2C
		accel->writeCNFG(1, &status);

		// Set the counter to 100 kbps
		accel->writeCNTR(213, &status);

		// The device identification number should be 0x2a
		assert(readRegister(kReg_WhoAmI) == 0x2a);
	}
}

static void writeRegister(Register reg, uint8_t data) {
	int32_t status = 0;
	uint32_t initialTime;

	accel->writeADDR(kSendAddress, &status);

	// Send a start transmit/receive message with the register address
	accel->writeCNTL(kControlStart | kControlTxRx, &status);
	accel->writeDATO(reg, &status);
	accel->strobeGO(&status);

	// Execute and wait until it's done (up to a millisecond)
	initialTime = getFPGATime(&status);
	while(accel->readSTAT(&status) & 1) {
		if(getFPGATime(&status) > initialTime + 1000) break;
	}

	// Send a stop transmit/receive message with the data
	accel->writeCNTL(kControlStop | kControlTxRx, &status);
	accel->writeDATO(data, &status);
	accel->strobeGO(&status);

	// Execute and wait until it's done (up to a millisecond)
	initialTime = getFPGATime(&status);
	while(accel->readSTAT(&status) & 1) {
		if(getFPGATime(&status) > initialTime + 1000) break;
	}

	fflush(stdout);
}

static uint8_t readRegister(Register reg) {
	int32_t status = 0;
	uint32_t initialTime;

	// Send a start transmit/receive message with the register address
	accel->writeADDR(kSendAddress, &status);
	accel->writeCNTL(kControlStart | kControlTxRx, &status);
	accel->writeDATO(reg, &status);
	accel->strobeGO(&status);

	// Execute and wait until it's done (up to a millisecond)
	initialTime = getFPGATime(&status);
	while(accel->readSTAT(&status) & 1) {
		if(getFPGATime(&status) > initialTime + 1000) break;
	}

	// Receive a message with the data and stop
	accel->writeADDR(kReceiveAddress, &status);
	accel->writeCNTL(kControlStart | kControlStop | kControlTxRx, &status);
	accel->strobeGO(&status);

	// Execute and wait until it's done (up to a millisecond)
	initialTime = getFPGATime(&status);
	while(accel->readSTAT(&status) & 1) {
		if(getFPGATime(&status) > initialTime + 1000) break;
	}

	fflush(stdout);

	return accel->readDATI(&status);
}

/**
 * Convert a 12-bit raw acceleration value into a scaled double in units of
 * 1 g-force, taking into account the accelerometer range.
 */
static double unpackAxis(int16_t raw) {
	// The raw value is actually 12 bits, not 16, so we need to propogate the
	// 2's complement sign bit to the unused 4 bits for this to work with
	// negative numbers.
	raw <<= 4;
	raw >>= 4;

	switch(accelerometerRange) {
	case kRange_2G: return raw / 1024.0;
	case kRange_4G: return raw / 512.0;
	case kRange_8G: return raw / 256.0;
	default: return 0.0;
	}
}

/**
 * Set the accelerometer to active or standby mode.  It must be in standby
 * mode to change any configuration.
 */
void setAccelerometerActive(bool active) {
	initializeAccelerometer();

	uint8_t ctrlReg1 = readRegister(kReg_CtrlReg1);
	ctrlReg1 &= ~1; // Clear the existing active bit
	writeRegister(kReg_CtrlReg1, ctrlReg1 | (active? 1 : 0));
}

/**
 * Set the range of values that can be measured (either 2, 4, or 8 g-forces).
 * The accelerometer should be in standby mode when this is called.
 */
void setAccelerometerRange(AccelerometerRange range) {
	initializeAccelerometer();

	accelerometerRange = range;

	uint8_t xyzDataCfg = readRegister(kReg_XYZDataCfg);
	xyzDataCfg &= ~3; // Clear the existing two range bits
	writeRegister(kReg_XYZDataCfg, xyzDataCfg | range);
}

/**
 * Get the x-axis acceleration
 *
 * This is a floating point value in units of 1 g-force
 */
double getAccelerometerX() {
	initializeAccelerometer();

	int raw = (readRegister(kReg_OutXMSB) << 4) | (readRegister(kReg_OutXLSB) >> 4);
	return unpackAxis(raw);
}

/**
 * Get the y-axis acceleration
 *
 * This is a floating point value in units of 1 g-force
 */
double getAccelerometerY() {
	initializeAccelerometer();

	int raw = (readRegister(kReg_OutYMSB) << 4) | (readRegister(kReg_OutYLSB) >> 4);
	return unpackAxis(raw);
}

/**
 * Get the z-axis acceleration
 *
 * This is a floating point value in units of 1 g-force
 */
double getAccelerometerZ() {
	initializeAccelerometer();

	int raw = (readRegister(kReg_OutZMSB) << 4) | (readRegister(kReg_OutZLSB) >> 4);
	return unpackAxis(raw);
}