File content as of revision 3:ce75ca8e2011:

// Most of the functionality of this library is based on the VL53L0X API
// provided by ST (STSW-IMG005), and some of the explanatory comments are quoted
// or paraphrased from the API source code, API user manual (UM2039), and the
// VL53L0X datasheet.

#include <VL53L0X_SH.h>
#include "mbed.h"
// Defines /////////////////////////////////////////////////////////////////////

// The Arduino two-wire interface uses a 7-bit number for the address,
// and sets the last bit correctly based on reads and writes
#define ADDRESS_DEFAULT 0b0101001

// Record the current time to check an upcoming timeout against
//#define startTimeout() (timeout_start_ms = millis())

// Check if timeout is enabled (set to nonzero value) and has expired
//#define checkTimeoutExpired() (io_timeout > 0 && ((short)millis() - timeout_start_ms) > io_timeout)

// Decode VCSEL (vertical cavity surface emitting laser) pulse period in PCLKs
// from register value
// based on VL53L0X_decode_vcsel_period()
#define decodeVcselPeriod(reg_val)      (((reg_val) + 1) << 1)

// Encode VCSEL pulse period register value from period in PCLKs
// based on VL53L0X_encode_vcsel_period()
#define encodeVcselPeriod(period_pclks) (((period_pclks) >> 1) - 1)

// Calculate macro period in *nanoseconds* from VCSEL period in PCLKs
// based on VL53L0X_calc_macro_period_ps()
// PLL_period_ps = 1655; macro_period_vclks = 2304
#define calcMacroPeriod(vcsel_period_pclks) ((((long)2304 * (vcsel_period_pclks) * 1655) + 500) / 1000)

// Constructors ////////////////////////////////////////////////////////////////
I2C         i2c(D14, D15);      //I2C reg(SDA, SCL)

VL53L0X::VL53L0X(void)
    : address(ADDRESS_DEFAULT)
    , io_timeout(0) // no timeout
    , did_timeout(false)
{
}

// Public Methods //////////////////////////////////////////////////////////////

void VL53L0X::setAddress(char new_addr)
{
    writeReg(I2C_SLAVE_DEVICE_ADDRESS, new_addr & 0x7F);
    address = new_addr;
}

// Initialize sensor using sequence based on VL53L0X_DataInit(),
// VL53L0X_StaticInit(), and VL53L0X_PerformRefCalibration().
// This function does not perform reference SPAD calibration
// (VL53L0X_PerformRefSpadManagement()), since the API user manual says that it
// is performed by ST on the bare modules; it seems like that should work well
// enough unless a cover glass is added.
// If io_2v8 (optional) is true or not given, the sensor is configured for 2V8
// mode.
bool VL53L0X::init(bool io_2v8)
{
    if (io_2v8) {
        writeReg(VHV_CONFIG_PAD_SCL_SDA__EXTSUP_HV,
                 readReg(VHV_CONFIG_PAD_SCL_SDA__EXTSUP_HV) | 0x01); // set bit 0
    }
    // "Set I2C standard mode"
    writeReg(0x88, 0x00);
    writeReg(0x80, 0x01);
    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);
    stop_variable = readReg(0x91);
    writeReg(0x00, 0x01);
    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x00);

    // disable SIGNAL_RATE_MSRC (bit 1) and SIGNAL_RATE_PRE_RANGE (bit 4) limit checks
    writeReg(MSRC_CONFIG_CONTROL, readReg(MSRC_CONFIG_CONTROL) | 0x12);

    // set final range signal rate limit to 0.25 MCPS (million counts per second)
    setSignalRateLimit(0.25);

    writeReg(SYSTEM_SEQUENCE_CONFIG, 0xFF);

    // VL53L0X_DataInit() end

    // VL53L0X_StaticInit() begin

    char spad_count;
    bool spad_type_is_aperture;
    if (!getSpadInfo(&spad_count, &spad_type_is_aperture)) {
        return false;
    }

    // The SPAD map (RefGoodSpadMap) is read by VL53L0X_get_info_from_device() in
    // the API, but the same data seems to be more easily readable from
    // GLOBAL_CONFIG_SPAD_ENABLES_REF_0 through _6, so read it from there
    char ref_spad_map[6];
    readMulti(GLOBAL_CONFIG_SPAD_ENABLES_REF_0, ref_spad_map, 6);

    // -- VL53L0X_set_reference_spads() begin (assume NVM values are valid)

    writeReg(0xFF, 0x01);
    writeReg(DYNAMIC_SPAD_REF_EN_START_OFFSET, 0x00);
    writeReg(DYNAMIC_SPAD_NUM_REQUESTED_REF_SPAD, 0x2C);
    writeReg(0xFF, 0x00);
    writeReg(GLOBAL_CONFIG_REF_EN_START_SELECT, 0xB4);

    char first_spad_to_enable = spad_type_is_aperture ? 12 : 0; // 12 is the first aperture spad
    char spads_enabled = 0;

    for (char i = 0; i < 48; i++) {
        if (i < first_spad_to_enable || spads_enabled == spad_count) {
            // This bit is lower than the first one that should be enabled, or
            // (reference_spad_count) bits have already been enabled, so zero this bit
            ref_spad_map[i / 8] &= ~(1 << (i % 8));
        } else if ((ref_spad_map[i / 8] >> (i % 8)) & 0x1) {
            spads_enabled++;
        }
    }

    writeMulti(GLOBAL_CONFIG_SPAD_ENABLES_REF_0, ref_spad_map, 6);

    // -- VL53L0X_set_reference_spads() end

    // -- VL53L0X_load_tuning_settings() begin
    // DefaultTuningSettings from vl53l0x_tuning.h

    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);

    writeReg(0xFF, 0x00);
    writeReg(0x09, 0x00);
    writeReg(0x10, 0x00);
    writeReg(0x11, 0x00);

    writeReg(0x24, 0x01);
    writeReg(0x25, 0xFF);
    writeReg(0x75, 0x00);

    writeReg(0xFF, 0x01);
    writeReg(0x4E, 0x2C);
    writeReg(0x48, 0x00);
    writeReg(0x30, 0x20);

    writeReg(0xFF, 0x00);
    writeReg(0x30, 0x09);
    writeReg(0x54, 0x00);
    writeReg(0x31, 0x04);
    writeReg(0x32, 0x03);
    writeReg(0x40, 0x83);
    writeReg(0x46, 0x25);
    writeReg(0x60, 0x00);
    writeReg(0x27, 0x00);
    writeReg(0x50, 0x06);
    writeReg(0x51, 0x00);
    writeReg(0x52, 0x96);
    writeReg(0x56, 0x08);
    writeReg(0x57, 0x30);
    writeReg(0x61, 0x00);
    writeReg(0x62, 0x00);
    writeReg(0x64, 0x00);
    writeReg(0x65, 0x00);
    writeReg(0x66, 0xA0);

    writeReg(0xFF, 0x01);
    writeReg(0x22, 0x32);
    writeReg(0x47, 0x14);
    writeReg(0x49, 0xFF);
    writeReg(0x4A, 0x00);

    writeReg(0xFF, 0x00);
    writeReg(0x7A, 0x0A);
    writeReg(0x7B, 0x00);
    writeReg(0x78, 0x21);

    writeReg(0xFF, 0x01);
    writeReg(0x23, 0x34);
    writeReg(0x42, 0x00);
    writeReg(0x44, 0xFF);
    writeReg(0x45, 0x26);
    writeReg(0x46, 0x05);
    writeReg(0x40, 0x40);
    writeReg(0x0E, 0x06);
    writeReg(0x20, 0x1A);
    writeReg(0x43, 0x40);

    writeReg(0xFF, 0x00);
    writeReg(0x34, 0x03);
    writeReg(0x35, 0x44);

    writeReg(0xFF, 0x01);
    writeReg(0x31, 0x04);
    writeReg(0x4B, 0x09);
    writeReg(0x4C, 0x05);
    writeReg(0x4D, 0x04);

    writeReg(0xFF, 0x00);
    writeReg(0x44, 0x00);
    writeReg(0x45, 0x20);
    writeReg(0x47, 0x08);
    writeReg(0x48, 0x28);
    writeReg(0x67, 0x00);
    writeReg(0x70, 0x04);
    writeReg(0x71, 0x01);
    writeReg(0x72, 0xFE);
    writeReg(0x76, 0x00);
    writeReg(0x77, 0x00);

    writeReg(0xFF, 0x01);
    writeReg(0x0D, 0x01);

    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x01);
    writeReg(0x01, 0xF8);

    writeReg(0xFF, 0x01);
    writeReg(0x8E, 0x01);
    writeReg(0x00, 0x01);
    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x00);

    // -- VL53L0X_load_tuning_settings() end

    // "Set interrupt config to new sample ready"
    // -- VL53L0X_SetGpioConfig() begin

    writeReg(SYSTEM_INTERRUPT_CONFIG_GPIO, 0x04);
    writeReg(GPIO_HV_MUX_ACTIVE_HIGH, readReg(GPIO_HV_MUX_ACTIVE_HIGH) & ~0x10); // active low
    writeReg(SYSTEM_INTERRUPT_CLEAR, 0x01);

    // -- VL53L0X_SetGpioConfig() end

    measurement_timing_budget_us = getMeasurementTimingBudget();

    // "Disable MSRC and TCC by default"
    // MSRC = Minimum Signal Rate Check
    // TCC = Target CentreCheck
    // -- VL53L0X_SetSequenceStepEnable() begin

    writeReg(SYSTEM_SEQUENCE_CONFIG, 0xE8);

    // -- VL53L0X_SetSequenceStepEnable() end

    // "Recalculate timing budget"
    setMeasurementTimingBudget(measurement_timing_budget_us);

    // VL53L0X_StaticInit() end

    // VL53L0X_PerformRefCalibration() begin (VL53L0X_perform_ref_calibration())

    // -- VL53L0X_perform_vhv_calibration() begin

    writeReg(SYSTEM_SEQUENCE_CONFIG, 0x01);
    if (!performSingleRefCalibration(0x40)) {
        return false;
    }

    // -- VL53L0X_perform_vhv_calibration() end

    // -- VL53L0X_perform_phase_calibration() begin

    writeReg(SYSTEM_SEQUENCE_CONFIG, 0x02);
    if (!performSingleRefCalibration(0x00)) {
        return false;
    }

    // -- VL53L0X_perform_phase_calibration() end

    // "restore the previous Sequence Config"
    writeReg(SYSTEM_SEQUENCE_CONFIG, 0xE8);

    // VL53L0X_PerformRefCalibration() end

    return true;
}

// Write an 8-bit register
void VL53L0X::writeReg(char reg, char value)
{
    data_w_2[0] = reg;
    data_w_2[1] = value;
    i2c.write( address<<1 | 0x00, data_w_2, 2, 0);
}

// Write a 16-bit register
void VL53L0X::writeReg16Bit(char reg, short value)
{
    data_w_3[0] = reg;
    data_w_3[1] = (value >> 8) & 0xFF;
    data_w_3[2] = (value     ) & 0xFF;
    i2c.write( address<<1 | 0x00, data_w_3, 3, 0);
}

// Write a 32-bit register
void VL53L0X::writeReg32Bit(char reg, long value)
{
    data_w_5[0] = reg;
    data_w_5[1] = (value >> 24) & 0xFF;
    data_w_5[2] = (value >> 16) & 0xFF;
    data_w_5[3] = (value >>  8) & 0xFF;
    data_w_5[4] = (value      ) & 0xFF;
    i2c.write( address<<1 | 0x00, data_w_5, 5, 0);
}

// Read an 8-bit register
char VL53L0X::readReg(char reg)
{
    char value[1];
    data_r_1[0] = reg;
    i2c.write( address<<1 | 0x00, data_r_1, 1, 0);
    i2c.read ( address<<1 | 0x01, value, 1, 0);
    return value[0];
}

// Read a 16-bit register
short VL53L0X::readReg16Bit(char reg)
{
    short value;
    data_r_1[0] = reg;
    i2c.write( address<<1 | 0x00, data_r_1, 1, 0);
    i2c.read ( address<<1 | 0x01, data_r_2, 2, 0);
    value = data_r_2[0] << 8 | data_r_2[1];
    return value;
}

// Read a 32-bit register
long VL53L0X::readReg32Bit(char reg)
{
    long value;
    data_r_1[0] = reg;
    i2c.write( address<<1 | 0x00, data_r_1, 1, 0);
    i2c.read ( address<<1 | 0x01, data_r_4, 4, 0);
    value  = data_r_4[0] << 24;
    value |= data_r_4[1] << 16;
    value |= data_r_4[2] <<  8;
    value |= data_r_4[3]      ;
    return value;
}

// Write an arbitrary number of bytes from the given array to the sensor,
// starting at the given register
void VL53L0X::writeMulti(char reg, char const * src, char count)
{
    char data_w_n[count];
    data_w_n[0] = reg;
    for(int i=0; i<count; i++) {
        data_w_n[i+1] = *(src+i);
    }
    i2c.write( address<<1 | 0x00, data_w_n, count, 0);
}

// Read an arbitrary number of bytes from the sensor, starting at the given
// register, into the given array
void VL53L0X::readMulti(char reg, char * dst, char count)
{
    char data_r_n[count];
    data_r_1[0] = reg;
    i2c.write( address<<1 | 0x00, data_r_1, 1, 0);
    i2c.read ( address<<1 | 0x01, data_r_n, count, 0);
    for(int i=0; i<count; i++) {
        *(dst+i) = data_r_n[i];
    }
}

// Set the return signal rate limit check value in units of MCPS (mega counts
// per second). "This represents the amplitude of the signal reflected from the
// target and detected by the device"; setting this limit presumably determines
// the minimum measurement necessary for the sensor to report a valid reading.
// Setting a lower limit increases the potential range of the sensor but also
// seems to increase the likelihood of getting an inaccurate reading because of
// unwanted reflections from objects other than the intended target.
// Defaults to 0.25 MCPS as initialized by the ST API and this library.
bool VL53L0X::setSignalRateLimit(float limit_Mcps)
{
    if (limit_Mcps < 0 || limit_Mcps > 511.99f) {
        return false;
    }

    // Q9.7 fixed point format (9 integer bits, 7 fractional bits)
    writeReg16Bit(FINAL_RANGE_CONFIG_MIN_COUNT_RATE_RTN_LIMIT, limit_Mcps * (1 << 7));
    return true;
}

// Get the return signal rate limit check value in MCPS
float VL53L0X::getSignalRateLimit(void)
{
    return (float)readReg16Bit(FINAL_RANGE_CONFIG_MIN_COUNT_RATE_RTN_LIMIT) / (1 << 7);
}

// Set the measurement timing budget in microseconds, which is the time allowed
// for one measurement; the ST API and this library take care of splitting the
// timing budget among the sub-steps in the ranging sequence. A longer timing
// budget allows for more accurate measurements. Increasing the budget by a
// factor of N decreases the range measurement standard deviation by a factor of
// sqrt(N). Defaults to about 33 milliseconds; the minimum is 20 ms.
// based on VL53L0X_set_measurement_timing_budget_micro_seconds()
bool VL53L0X::setMeasurementTimingBudget(long budget_us)
{
    SequenceStepEnables enables;
    SequenceStepTimeouts timeouts;

    short const StartOverhead      = 1320; // note that this is different than the value in get_
    short const EndOverhead        = 960;
    short const MsrcOverhead       = 660;
    short const TccOverhead        = 590;
    short const DssOverhead        = 690;
    short const PreRangeOverhead   = 660;
    short const FinalRangeOverhead = 550;

    long const MinTimingBudget = 20000;

    if (budget_us < MinTimingBudget) {
        return false;
    }

    long used_budget_us = StartOverhead + EndOverhead;

    getSequenceStepEnables(&enables);
    getSequenceStepTimeouts(&enables, &timeouts);

    if (enables.tcc) {
        used_budget_us += (timeouts.msrc_dss_tcc_us + TccOverhead);
    }

    if (enables.dss) {
        used_budget_us += 2 * (timeouts.msrc_dss_tcc_us + DssOverhead);
    } else if (enables.msrc) {
        used_budget_us += (timeouts.msrc_dss_tcc_us + MsrcOverhead);
    }

    if (enables.pre_range) {
        used_budget_us += (timeouts.pre_range_us + PreRangeOverhead);
    }

    if (enables.final_range) {
        used_budget_us += FinalRangeOverhead;

        // "Note that the final range timeout is determined by the timing
        // budget and the sum of all other timeouts within the sequence.
        // If there is no room for the final range timeout, then an error
        // will be set. Otherwise the remaining time will be applied to
        // the final range."

        if (used_budget_us > budget_us) {
            // "Requested timeout too big."
            return false;
        }

        long final_range_timeout_us = budget_us - used_budget_us;

        // set_sequence_step_timeout() begin
        // (SequenceStepId == VL53L0X_SEQUENCESTEP_FINAL_RANGE)

        // "For the final range timeout, the pre-range timeout
        //  must be added. To do this both final and pre-range
        //  timeouts must be expressed in macro periods MClks
        //  because they have different vcsel periods."

        short final_range_timeout_mclks =
            timeoutMicrosecondsToMclks(final_range_timeout_us,
                                       timeouts.final_range_vcsel_period_pclks);

        if (enables.pre_range) {
            final_range_timeout_mclks += timeouts.pre_range_mclks;
        }

        writeReg16Bit(FINAL_RANGE_CONFIG_TIMEOUT_MACROP_HI,
                      encodeTimeout(final_range_timeout_mclks));

        // set_sequence_step_timeout() end

        measurement_timing_budget_us = budget_us; // store for internal reuse
    }
    return true;
}

// Get the measurement timing budget in microseconds
// based on VL53L0X_get_measurement_timing_budget_micro_seconds()
// in us
long VL53L0X::getMeasurementTimingBudget(void)
{
    SequenceStepEnables enables;
    SequenceStepTimeouts timeouts;

    short const StartOverhead     = 1910; // note that this is different than the value in set_
    short const EndOverhead        = 960;
    short const MsrcOverhead       = 660;
    short const TccOverhead        = 590;
    short const DssOverhead        = 690;
    short const PreRangeOverhead   = 660;
    short const FinalRangeOverhead = 550;

    // "Start and end overhead times always present"
    long budget_us = StartOverhead + EndOverhead;

    getSequenceStepEnables(&enables);
    getSequenceStepTimeouts(&enables, &timeouts);

    if (enables.tcc) {
        budget_us += (timeouts.msrc_dss_tcc_us + TccOverhead);
    }

    if (enables.dss) {
        budget_us += 2 * (timeouts.msrc_dss_tcc_us + DssOverhead);
    } else if (enables.msrc) {
        budget_us += (timeouts.msrc_dss_tcc_us + MsrcOverhead);
    }

    if (enables.pre_range) {
        budget_us += (timeouts.pre_range_us + PreRangeOverhead);
    }

    if (enables.final_range) {
        budget_us += (timeouts.final_range_us + FinalRangeOverhead);
    }

    measurement_timing_budget_us = budget_us; // store for internal reuse
    return budget_us;
}

// Set the VCSEL (vertical cavity surface emitting laser) pulse period for the
// given period type (pre-range or final range) to the given value in PCLKs.
// Longer periods seem to increase the potential range of the sensor.
// Valid values are (even numbers only):
//  pre:  12 to 18 (initialized default: 14)
//  final: 8 to 14 (initialized default: 10)
// based on VL53L0X_set_vcsel_pulse_period()
bool VL53L0X::setVcselPulsePeriod(vcselPeriodType type, char period_pclks)
{
    char vcsel_period_reg = encodeVcselPeriod(period_pclks);

    SequenceStepEnables enables;
    SequenceStepTimeouts timeouts;

    getSequenceStepEnables(&enables);
    getSequenceStepTimeouts(&enables, &timeouts);

    // "Apply specific settings for the requested clock period"
    // "Re-calculate and apply timeouts, in macro periods"

    // "When the VCSEL period for the pre or final range is changed,
    // the corresponding timeout must be read from the device using
    // the current VCSEL period, then the new VCSEL period can be
    // applied. The timeout then must be written back to the device
    // using the new VCSEL period.
    //
    // For the MSRC timeout, the same applies - this timeout being
    // dependant on the pre-range vcsel period."


    if (type == VcselPeriodPreRange) {
        // "Set phase check limits"
        switch (period_pclks) {
            case 12:
                writeReg(PRE_RANGE_CONFIG_VALID_PHASE_HIGH, 0x18);
                break;

            case 14:
                writeReg(PRE_RANGE_CONFIG_VALID_PHASE_HIGH, 0x30);
                break;

            case 16:
                writeReg(PRE_RANGE_CONFIG_VALID_PHASE_HIGH, 0x40);
                break;

            case 18:
                writeReg(PRE_RANGE_CONFIG_VALID_PHASE_HIGH, 0x50);
                break;

            default:
                // invalid period
                return false;
        }
        writeReg(PRE_RANGE_CONFIG_VALID_PHASE_LOW, 0x08);

        // apply new VCSEL period
        writeReg(PRE_RANGE_CONFIG_VCSEL_PERIOD, vcsel_period_reg);

        // update timeouts

        // set_sequence_step_timeout() begin
        // (SequenceStepId == VL53L0X_SEQUENCESTEP_PRE_RANGE)

        short new_pre_range_timeout_mclks =
            timeoutMicrosecondsToMclks(timeouts.pre_range_us, period_pclks);

        writeReg16Bit(PRE_RANGE_CONFIG_TIMEOUT_MACROP_HI,
                      encodeTimeout(new_pre_range_timeout_mclks));

        // set_sequence_step_timeout() end

        // set_sequence_step_timeout() begin
        // (SequenceStepId == VL53L0X_SEQUENCESTEP_MSRC)

        short new_msrc_timeout_mclks =
            timeoutMicrosecondsToMclks(timeouts.msrc_dss_tcc_us, period_pclks);

        writeReg(MSRC_CONFIG_TIMEOUT_MACROP,
                 (new_msrc_timeout_mclks > 256) ? 255 : (new_msrc_timeout_mclks - 1));

        // set_sequence_step_timeout() end
    } else if (type == VcselPeriodFinalRange) {
        switch (period_pclks) {
            case 8:
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_HIGH, 0x10);
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_LOW,  0x08);
                writeReg(GLOBAL_CONFIG_VCSEL_WIDTH, 0x02);
                writeReg(ALGO_PHASECAL_CONFIG_TIMEOUT, 0x0C);
                writeReg(0xFF, 0x01);
                writeReg(ALGO_PHASECAL_LIM, 0x30);
                writeReg(0xFF, 0x00);
                break;

            case 10:
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_HIGH, 0x28);
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_LOW,  0x08);
                writeReg(GLOBAL_CONFIG_VCSEL_WIDTH, 0x03);
                writeReg(ALGO_PHASECAL_CONFIG_TIMEOUT, 0x09);
                writeReg(0xFF, 0x01);
                writeReg(ALGO_PHASECAL_LIM, 0x20);
                writeReg(0xFF, 0x00);
                break;

            case 12:
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_HIGH, 0x38);
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_LOW,  0x08);
                writeReg(GLOBAL_CONFIG_VCSEL_WIDTH, 0x03);
                writeReg(ALGO_PHASECAL_CONFIG_TIMEOUT, 0x08);
                writeReg(0xFF, 0x01);
                writeReg(ALGO_PHASECAL_LIM, 0x20);
                writeReg(0xFF, 0x00);
                break;

            case 14:
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_HIGH, 0x48);
                writeReg(FINAL_RANGE_CONFIG_VALID_PHASE_LOW,  0x08);
                writeReg(GLOBAL_CONFIG_VCSEL_WIDTH, 0x03);
                writeReg(ALGO_PHASECAL_CONFIG_TIMEOUT, 0x07);
                writeReg(0xFF, 0x01);
                writeReg(ALGO_PHASECAL_LIM, 0x20);
                writeReg(0xFF, 0x00);
                break;

            default:
                // invalid period
                return false;
        }

        // apply new VCSEL period
        writeReg(FINAL_RANGE_CONFIG_VCSEL_PERIOD, vcsel_period_reg);

        // update timeouts

        // set_sequence_step_timeout() begin
        // (SequenceStepId == VL53L0X_SEQUENCESTEP_FINAL_RANGE)

        // "For the final range timeout, the pre-range timeout
        //  must be added. To do this both final and pre-range
        //  timeouts must be expressed in macro periods MClks
        //  because they have different vcsel periods."

        short new_final_range_timeout_mclks =
            timeoutMicrosecondsToMclks(timeouts.final_range_us, period_pclks);

        if (enables.pre_range) {
            new_final_range_timeout_mclks += timeouts.pre_range_mclks;
        }

        writeReg16Bit(FINAL_RANGE_CONFIG_TIMEOUT_MACROP_HI,
                      encodeTimeout(new_final_range_timeout_mclks));

        // set_sequence_step_timeout end
    } else {
        // invalid type
        return false;
    }

    // "Finally, the timing budget must be re-applied"

    setMeasurementTimingBudget(measurement_timing_budget_us);

    // "Perform the phase calibration. This is needed after changing on vcsel period."
    // VL53L0X_perform_phase_calibration() begin

    char sequence_config = readReg(SYSTEM_SEQUENCE_CONFIG);
    writeReg(SYSTEM_SEQUENCE_CONFIG, 0x02);
    performSingleRefCalibration(0x0);
    writeReg(SYSTEM_SEQUENCE_CONFIG, sequence_config);

    // VL53L0X_perform_phase_calibration() end

    return true;
}

// Get the VCSEL pulse period in PCLKs for the given period type.
// based on VL53L0X_get_vcsel_pulse_period()
char VL53L0X::getVcselPulsePeriod(vcselPeriodType type)
{
    if (type == VcselPeriodPreRange) {
        return decodeVcselPeriod(readReg(PRE_RANGE_CONFIG_VCSEL_PERIOD));
    } else if (type == VcselPeriodFinalRange) {
        return decodeVcselPeriod(readReg(FINAL_RANGE_CONFIG_VCSEL_PERIOD));
    } else {
        return 255;
    }
}

// Start continuous ranging measurements. If period_ms (optional) is 0 or not
// given, continuous back-to-back mode is used (the sensor takes measurements as
// often as possible); otherwise, continuous timed mode is used, with the given
// inter-measurement period in milliseconds determining how often the sensor
// takes a measurement.
// based on VL53L0X_StartMeasurement()
void VL53L0X::startContinuous(long period_ms)
{
    writeReg(0x80, 0x01);
    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);
    writeReg(0x91, stop_variable);
    writeReg(0x00, 0x01);
    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x00);

    if (period_ms != 0) {
        // continuous timed mode

        // VL53L0X_SetInterMeasurementPeriodMilliSeconds() begin

        short osc_calibrate_val = readReg16Bit(OSC_CALIBRATE_VAL);

        if (osc_calibrate_val != 0) {
            period_ms *= osc_calibrate_val;
        }

        writeReg32Bit(SYSTEM_INTERMEASUREMENT_PERIOD, period_ms);

        // VL53L0X_SetInterMeasurementPeriodMilliSeconds() end

        writeReg(SYSRANGE_START, 0x04); // VL53L0X_REG_SYSRANGE_MODE_TIMED
    } else {
        // continuous back-to-back mode
        writeReg(SYSRANGE_START, 0x02); // VL53L0X_REG_SYSRANGE_MODE_BACKTOBACK
    }
}

// Stop continuous measurements
// based on VL53L0X_StopMeasurement()
void VL53L0X::stopContinuous(void)
{
    writeReg(SYSRANGE_START, 0x01); // VL53L0X_REG_SYSRANGE_MODE_SINGLESHOT

    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);
    writeReg(0x91, 0x00);
    writeReg(0x00, 0x01);
    writeReg(0xFF, 0x00);
}

// Returns a range reading in millimeters when continuous mode is active
// (readRangeSingleMillimeters() also calls this function after starting a
// single-shot range measurement)
short VL53L0X::readRangeContinuousMillimeters(void)
{
//    startTimeout();
//    while ((readReg(RESULT_INTERRUPT_STATUS) & 0x07) == 0) {
//        if (checkTimeoutExpired()) {
//            did_timeout = true;
//            return 32767;
//        }
//    }

    // assumptions: Linearity Corrective Gain is 1000 (default);
    // fractional ranging is not enabled
    short range = readReg16Bit(RESULT_RANGE_STATUS + 10);

    writeReg(SYSTEM_INTERRUPT_CLEAR, 0x01);

    return range;
}

// Performs a single-shot range measurement and returns the reading in
// millimeters
// based on VL53L0X_PerformSingleRangingMeasurement()
short VL53L0X::readRangeSingleMillimeters(void)
{
    writeReg(0x80, 0x01);
    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);
    writeReg(0x91, stop_variable);
    writeReg(0x00, 0x01);
    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x00);

    writeReg(SYSRANGE_START, 0x01);

    // "Wait until start bit has been cleared"
//    startTimeout();
//    while (readReg(SYSRANGE_START) & 0x01) {
//        if (checkTimeoutExpired()) {
//            did_timeout = true;
//            return 32767;
//        }
//    }

    return readRangeContinuousMillimeters();
}

// Did a timeout occur in one of the read functions since the last call to
// timeoutOccurred()?
bool VL53L0X::timeoutOccurred()
{
    bool tmp = did_timeout;
    did_timeout = false;
    return tmp;
}

// Private Methods /////////////////////////////////////////////////////////////

// Get reference SPAD (single photon avalanche diode) count and type
// based on VL53L0X_get_info_from_device(),
// but only gets reference SPAD count and type
bool VL53L0X::getSpadInfo(char * count, bool * type_is_aperture)
{
    char tmp;

    writeReg(0x80, 0x01);
    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x00);

    writeReg(0xFF, 0x06);
    writeReg(0x83, readReg(0x83) | 0x04);
    writeReg(0xFF, 0x07);
    writeReg(0x81, 0x01);

    writeReg(0x80, 0x01);

    writeReg(0x94, 0x6b);
    writeReg(0x83, 0x00);
//    startTimeout();
    wait_ms(1);
    while (readReg(0x83) == 0x00) {
//        if (checkTimeoutExpired()) {
//            return false;
//        }
    }
    writeReg(0x83, 0x01);
    tmp = readReg(0x92);

    *count = tmp & 0x7f;
    *type_is_aperture = (tmp >> 7) & 0x01;

    writeReg(0x81, 0x00);
    writeReg(0xFF, 0x06);
    writeReg(0x83, readReg( 0x83  & ~0x04));
    writeReg(0xFF, 0x01);
    writeReg(0x00, 0x01);

    writeReg(0xFF, 0x00);
    writeReg(0x80, 0x00);

    return true;
}

// Get sequence step enables
// based on VL53L0X_GetSequenceStepEnables()
void VL53L0X::getSequenceStepEnables(SequenceStepEnables * enables)
{
    char sequence_config = readReg(SYSTEM_SEQUENCE_CONFIG);

    enables->tcc          = (sequence_config >> 4) & 0x1;
    enables->dss          = (sequence_config >> 3) & 0x1;
    enables->msrc         = (sequence_config >> 2) & 0x1;
    enables->pre_range    = (sequence_config >> 6) & 0x1;
    enables->final_range  = (sequence_config >> 7) & 0x1;
}

// Get sequence step timeouts
// based on get_sequence_step_timeout(),
// but gets all timeouts instead of just the requested one, and also stores
// intermediate values
void VL53L0X::getSequenceStepTimeouts(SequenceStepEnables const * enables, SequenceStepTimeouts * timeouts)
{
    timeouts->pre_range_vcsel_period_pclks = getVcselPulsePeriod(VcselPeriodPreRange);

    timeouts->msrc_dss_tcc_mclks = readReg(MSRC_CONFIG_TIMEOUT_MACROP) + 1;
    timeouts->msrc_dss_tcc_us =
        timeoutMclksToMicroseconds(timeouts->msrc_dss_tcc_mclks,
                                   timeouts->pre_range_vcsel_period_pclks);

    timeouts->pre_range_mclks =
        decodeTimeout(readReg16Bit(PRE_RANGE_CONFIG_TIMEOUT_MACROP_HI));
    timeouts->pre_range_us =
        timeoutMclksToMicroseconds(timeouts->pre_range_mclks,
                                   timeouts->pre_range_vcsel_period_pclks);

    timeouts->final_range_vcsel_period_pclks = getVcselPulsePeriod(VcselPeriodFinalRange);

    timeouts->final_range_mclks =
        decodeTimeout(readReg16Bit(FINAL_RANGE_CONFIG_TIMEOUT_MACROP_HI));

    if (enables->pre_range) {
        timeouts->final_range_mclks -= timeouts->pre_range_mclks;
    }

    timeouts->final_range_us =
        timeoutMclksToMicroseconds(timeouts->final_range_mclks,
                                   timeouts->final_range_vcsel_period_pclks);
}

// Decode sequence step timeout in MCLKs from register value
// based on VL53L0X_decode_timeout()
// Note: the original function returned a long, but the return value is
// always stored in a short.
short VL53L0X::decodeTimeout(short reg_val)
{
    // format: "(LSByte * 2^MSByte) + 1"
    return (short)((reg_val & 0x00FF) <<
                   (short)((reg_val & 0xFF00) >> 8)) + 1;
}

// Encode sequence step timeout register value from timeout in MCLKs
// based on VL53L0X_encode_timeout()
// Note: the original function took a short, but the argument passed to it
// is always a short.
short VL53L0X::encodeTimeout(short timeout_mclks)
{
    // format: "(LSByte * 2^MSByte) + 1"

    long ls_byte = 0;
    short ms_byte = 0;

    if (timeout_mclks > 0) {
        ls_byte = timeout_mclks - 1;

        while ((ls_byte & 0xFFFFFF00) > 0) {
            ls_byte >>= 1;
            ms_byte++;
        }

        return (ms_byte << 8) | (ls_byte & 0xFF);
    } else {
        return 0;
    }
}

// Convert sequence step timeout from MCLKs to microseconds with given VCSEL period in PCLKs
// based on VL53L0X_calc_timeout_us()
long VL53L0X::timeoutMclksToMicroseconds(short timeout_period_mclks, char vcsel_period_pclks)
{
    long macro_period_ns = calcMacroPeriod(vcsel_period_pclks);

    return ((timeout_period_mclks * macro_period_ns) + (macro_period_ns / 2)) / 1000;
}

// Convert sequence step timeout from microseconds to MCLKs with given VCSEL period in PCLKs
// based on VL53L0X_calc_timeout_mclks()
long VL53L0X::timeoutMicrosecondsToMclks(long timeout_period_us, char vcsel_period_pclks)
{
    long macro_period_ns = calcMacroPeriod(vcsel_period_pclks);

    return (((timeout_period_us * 1000) + (macro_period_ns / 2)) / macro_period_ns);
}


// based on VL53L0X_perform_single_ref_calibration()
bool VL53L0X::performSingleRefCalibration(char vhv_init_byte)
{
    writeReg(SYSRANGE_START, 0x01 | vhv_init_byte); // VL53L0X_REG_SYSRANGE_MODE_START_STOP

//    startTimeout();
    wait_ms(1);
    while ((readReg(RESULT_INTERRUPT_STATUS) & 0x07) == 0) {
//        if (checkTimeoutExpired()) {
//            return false;
//        }
    }

    writeReg(SYSTEM_INTERRUPT_CLEAR, 0x01);

    writeReg(SYSRANGE_START, 0x00);

    return true;
}