esp32-hal-spi.c

// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "esp32-hal-spi.h"
#include "esp32-hal.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/semphr.h"
#include "rom/ets_sys.h"
#include "esp_attr.h"
#include "esp_intr.h"
#include "rom/gpio.h"
#include "soc/spi_reg.h"
#include "soc/spi_struct.h"
#include "soc/io_mux_reg.h"
#include "soc/gpio_sig_map.h"
#include "soc/dport_reg.h"

#define SPI_CLK_IDX(p)  ((p==0)?SPICLK_OUT_IDX:((p==1)?SPICLK_OUT_IDX:((p==2)?HSPICLK_OUT_IDX:((p==3)?VSPICLK_OUT_IDX:0))))
#define SPI_MISO_IDX(p) ((p==0)?SPIQ_OUT_IDX:((p==1)?SPIQ_OUT_IDX:((p==2)?HSPIQ_OUT_IDX:((p==3)?VSPIQ_OUT_IDX:0))))
#define SPI_MOSI_IDX(p) ((p==0)?SPID_IN_IDX:((p==1)?SPID_IN_IDX:((p==2)?HSPID_IN_IDX:((p==3)?VSPID_IN_IDX:0))))

#define SPI_SPI_SS_IDX(n)   ((n==0)?SPICS0_OUT_IDX:((n==1)?SPICS1_OUT_IDX:((n==2)?SPICS2_OUT_IDX:SPICS0_OUT_IDX)))
#define SPI_HSPI_SS_IDX(n)   ((n==0)?HSPICS0_OUT_IDX:((n==1)?HSPICS1_OUT_IDX:((n==2)?HSPICS2_OUT_IDX:HSPICS0_OUT_IDX)))
#define SPI_VSPI_SS_IDX(n)   ((n==0)?VSPICS0_OUT_IDX:((n==1)?VSPICS1_OUT_IDX:((n==2)?VSPICS2_OUT_IDX:VSPICS0_OUT_IDX)))
#define SPI_SS_IDX(p, n)   ((p==0)?SPI_SPI_SS_IDX(n):((p==1)?SPI_SPI_SS_IDX(n):((p==2)?SPI_HSPI_SS_IDX(n):((p==3)?SPI_VSPI_SS_IDX(n):0))))

#define SPI_INUM(u)        (2)
#define SPI_INTR_SOURCE(u) ((u==0)?ETS_SPI0_INTR_SOURCE:((u==1)?ETS_SPI1_INTR_SOURCE:((u==2)?ETS_SPI2_INTR_SOURCE:((p==3)?ETS_SPI3_INTR_SOURCE:0))))

struct spi_struct_t {
    spi_dev_t * dev;
#if !CONFIG_DISABLE_HAL_LOCKS
    xSemaphoreHandle lock;
#endif
    uint8_t num;
};

#if CONFIG_DISABLE_HAL_LOCKS
#define SPI_MUTEX_LOCK()
#define SPI_MUTEX_UNLOCK()

static spi_t _spi_bus_array[4] = {
    {(volatile spi_dev_t *)(DR_REG_SPI0_BASE), 0},
    {(volatile spi_dev_t *)(DR_REG_SPI1_BASE), 1},
    {(volatile spi_dev_t *)(DR_REG_SPI2_BASE), 2},
    {(volatile spi_dev_t *)(DR_REG_SPI3_BASE), 3}
};
#else
#define SPI_MUTEX_LOCK()    do {} while (xSemaphoreTake(spi->lock, portMAX_DELAY) != pdPASS)
#define SPI_MUTEX_UNLOCK()  xSemaphoreGive(spi->lock)

static spi_t _spi_bus_array[4] = {
    {(volatile spi_dev_t *)(DR_REG_SPI0_BASE), NULL, 0},
    {(volatile spi_dev_t *)(DR_REG_SPI1_BASE), NULL, 1},
    {(volatile spi_dev_t *)(DR_REG_SPI2_BASE), NULL, 2},
    {(volatile spi_dev_t *)(DR_REG_SPI3_BASE), NULL, 3}
};
#endif

void spiAttachSCK(spi_t * spi, int8_t sck)
{
    if(!spi) {
        return;
    }
    if(sck < 0) {
        if(spi->num == HSPI) {
            sck = 14;
        } else if(spi->num == VSPI) {
            sck = 18;
        } else {
            sck = 6;
        }
    }
    pinMode(sck, OUTPUT);
    pinMatrixOutAttach(sck, SPI_CLK_IDX(spi->num), false, false);
}

void spiAttachMISO(spi_t * spi, int8_t miso)
{
    if(!spi) {
        return;
    }
    if(miso < 0) {
        if(spi->num == HSPI) {
            miso = 12;
        } else if(spi->num == VSPI) {
            miso = 19;
        } else {
            miso = 7;
        }
    }
    SPI_MUTEX_LOCK();
    pinMode(miso, INPUT);
    pinMatrixInAttach(miso, SPI_MISO_IDX(spi->num), false);
    SPI_MUTEX_UNLOCK();
}

void spiAttachMOSI(spi_t * spi, int8_t mosi)
{
    if(!spi) {
        return;
    }
    if(mosi < 0) {
        if(spi->num == HSPI) {
            mosi = 13;
        } else if(spi->num == VSPI) {
            mosi = 23;
        } else {
            mosi = 8;
        }
    }
    pinMode(mosi, OUTPUT);
    pinMatrixOutAttach(mosi, SPI_MOSI_IDX(spi->num), false, false);
}

void spiDetachSCK(spi_t * spi, int8_t sck)
{
    if(!spi) {
        return;
    }
    if(sck < 0) {
        if(spi->num == HSPI) {
            sck = 14;
        } else if(spi->num == VSPI) {
            sck = 18;
        } else {
            sck = 6;
        }
    }
    pinMatrixOutDetach(sck, false, false);
    pinMode(sck, INPUT);
}

void spiDetachMISO(spi_t * spi, int8_t miso)
{
    if(!spi) {
        return;
    }
    if(miso < 0) {
        if(spi->num == HSPI) {
            miso = 12;
        } else if(spi->num == VSPI) {
            miso = 19;
        } else {
            miso = 7;
        }
    }
    pinMatrixInDetach(SPI_MISO_IDX(spi->num), false, false);
    pinMode(miso, INPUT);
}

void spiDetachMOSI(spi_t * spi, int8_t mosi)
{
    if(!spi) {
        return;
    }
    if(mosi < 0) {
        if(spi->num == HSPI) {
            mosi = 13;
        } else if(spi->num == VSPI) {
            mosi = 23;
        } else {
            mosi = 8;
        }
    }
    pinMatrixOutDetach(mosi, false, false);
    pinMode(mosi, INPUT);
}

void spiAttachSS(spi_t * spi, uint8_t cs_num, int8_t ss)
{
    if(!spi) {
        return;
    }
    if(cs_num > 2) {
        return;
    }
    if(ss < 0) {
        cs_num = 0;
        if(spi->num == HSPI) {
            ss = 15;
        } else if(spi->num == VSPI) {
            ss = 5;
        } else {
            ss = 11;
        }
    }
    pinMode(ss, OUTPUT);
    pinMatrixOutAttach(ss, SPI_SS_IDX(spi->num, cs_num), false, false);
    spiEnableSSPins(spi, (1 << cs_num));
}

void spiDetachSS(spi_t * spi, int8_t ss)
{
    if(!spi) {
        return;
    }
    if(ss < 0) {
        if(spi->num == HSPI) {
            ss = 15;
        } else if(spi->num == VSPI) {
            ss = 5;
        } else {
            ss = 11;
        }
    }
    pinMatrixOutDetach(ss, false, false);
    pinMode(ss, INPUT);
}

void spiEnableSSPins(spi_t * spi, uint8_t cs_mask)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->pin.val &= ~(cs_mask & SPI_CS_MASK_ALL);
    SPI_MUTEX_UNLOCK();
}

void spiDisableSSPins(spi_t * spi, uint8_t cs_mask)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->pin.val |= (cs_mask & SPI_CS_MASK_ALL);
    SPI_MUTEX_UNLOCK();
}

void spiSSEnable(spi_t * spi)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->user.cs_setup = 1;
    spi->dev->user.cs_hold = 1;
    SPI_MUTEX_UNLOCK();
}

void spiSSDisable(spi_t * spi)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->user.cs_setup = 0;
    spi->dev->user.cs_hold = 0;
    SPI_MUTEX_UNLOCK();
}

void spiSSSet(spi_t * spi)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->pin.cs_keep_active = 1;
    SPI_MUTEX_UNLOCK();
}

void spiSSClear(spi_t * spi)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->pin.cs_keep_active = 0;
    SPI_MUTEX_UNLOCK();
}

uint32_t spiGetClockDiv(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    return spi->dev->clock.val;
}

void spiSetClockDiv(spi_t * spi, uint32_t clockDiv)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->clock.val = clockDiv;
    SPI_MUTEX_UNLOCK();
}

uint8_t spiGetDataMode(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    bool idleEdge = spi->dev->pin.ck_idle_edge;
    bool outEdge = spi->dev->user.ck_out_edge;
    if(idleEdge) {
        if(outEdge) {
            return SPI_MODE3;
        }
        return SPI_MODE2;
    }
    if(outEdge) {
        return SPI_MODE1;
    }
    return SPI_MODE0;
}

void spiSetDataMode(spi_t * spi, uint8_t dataMode)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    switch (dataMode) {
    case SPI_MODE1:
        spi->dev->pin.ck_idle_edge = 0;
        spi->dev->user.ck_out_edge = 1;
        break;
    case SPI_MODE2:
        spi->dev->pin.ck_idle_edge = 1;
        spi->dev->user.ck_out_edge = 0;
        break;
    case SPI_MODE3:
        spi->dev->pin.ck_idle_edge = 1;
        spi->dev->user.ck_out_edge = 1;
        break;
    case SPI_MODE0:
    default:
        spi->dev->pin.ck_idle_edge = 0;
        spi->dev->user.ck_out_edge = 0;
        break;
    }
    SPI_MUTEX_UNLOCK();
}

uint8_t spiGetBitOrder(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    return (spi->dev->ctrl.wr_bit_order | spi->dev->ctrl.rd_bit_order) == 0;
}

void spiSetBitOrder(spi_t * spi, uint8_t bitOrder)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    if (SPI_MSBFIRST == bitOrder) {
        spi->dev->ctrl.wr_bit_order = 0;
        spi->dev->ctrl.rd_bit_order = 0;
    } else if (SPI_LSBFIRST == bitOrder) {
        spi->dev->ctrl.wr_bit_order = 1;
        spi->dev->ctrl.rd_bit_order = 1;
    }
    SPI_MUTEX_UNLOCK();
}

void spiStopBus(spi_t * spi)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    spi->dev->slave.trans_done = 0;
    spi->dev->slave.slave_mode = 0;
    spi->dev->pin.val = 0;
    spi->dev->user.val = 0;
    spi->dev->user1.val = 0;
    spi->dev->ctrl.val = 0;
    spi->dev->ctrl1.val = 0;
    spi->dev->ctrl2.val = 0;
    spi->dev->clock.val = 0;
    SPI_MUTEX_UNLOCK();
}

spi_t * spiStartBus(uint8_t spi_num, uint32_t clockDiv, uint8_t dataMode, uint8_t bitOrder)
{
    if(spi_num > 3){
        return NULL;
    }

    spi_t * spi = &_spi_bus_array[spi_num];

#if !CONFIG_DISABLE_HAL_LOCKS
    if(spi->lock == NULL){
        spi->lock = xSemaphoreCreateMutex();
        if(spi->lock == NULL) {
            return NULL;
        }
    }
#endif

    if(spi_num == HSPI) {
        SET_PERI_REG_MASK(DPORT_PERIP_CLK_EN_REG, DPORT_SPI_CLK_EN_1);
        CLEAR_PERI_REG_MASK(DPORT_PERIP_RST_EN_REG, DPORT_SPI_RST_1);
    } else if(spi_num == VSPI) {
        SET_PERI_REG_MASK(DPORT_PERIP_CLK_EN_REG, DPORT_SPI_CLK_EN_2);
        CLEAR_PERI_REG_MASK(DPORT_PERIP_RST_EN_REG, DPORT_SPI_RST_2);
    } else {
        SET_PERI_REG_MASK(DPORT_PERIP_CLK_EN_REG, DPORT_SPI_CLK_EN);
        CLEAR_PERI_REG_MASK(DPORT_PERIP_RST_EN_REG, DPORT_SPI_RST);
    }

    spiStopBus(spi);
    spiSetDataMode(spi, dataMode);
    spiSetBitOrder(spi, bitOrder);
    spiSetClockDiv(spi, clockDiv);

    SPI_MUTEX_LOCK();
    spi->dev->user.usr_mosi = 1;
    spi->dev->user.usr_miso = 1;
    spi->dev->user.doutdin = 1;

    int i;
    for(i=0; i<16; i++) {
        spi->dev->data_buf[i] = 0x00000000;
    }
    SPI_MUTEX_UNLOCK();

    return spi;
}

void spiWaitReady(spi_t * spi)
{
    if(!spi) {
        return;
    }
    while(spi->dev->cmd.usr);
}

void spiWrite(spi_t * spi, uint32_t *data, uint8_t len)
{
    if(!spi) {
        return;
    }
    int i;
    if(len > 16) {
        len = 16;
    }
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = (len * 32) - 1;
    spi->dev->miso_dlen.usr_miso_dbitlen = (len * 32) - 1;
    for(i=0; i<len; i++) {
        spi->dev->data_buf[i] = data[i];
    }
    spi->dev->cmd.usr = 1;
    SPI_MUTEX_UNLOCK();
}

void spiRead(spi_t * spi, uint32_t *data, uint8_t len)
{
    if(!spi) {
        return;
    }
    int i;
    if(len > 16) {
        len = 16;
    }
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    for(i=0; i<len; i++) {
        data[i] = spi->dev->data_buf[i];
    }
    SPI_MUTEX_UNLOCK();
}

void spiWriteByte(spi_t * spi, uint8_t data)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = 7;
    spi->dev->miso_dlen.usr_miso_dbitlen = 7;
    spi->dev->data_buf[0] = data;
    spi->dev->cmd.usr = 1;
    SPI_MUTEX_UNLOCK();
}

uint8_t spiReadByte(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    uint8_t data;
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    data = spi->dev->data_buf[0] & 0xFF;
    SPI_MUTEX_UNLOCK();
    return data;
}

uint32_t __spiTranslate16(uint16_t data, bool msb)
{
    if(msb) {
        return (data >> 8) | (data << 8);
    } else {
        return data;
    }
}

uint32_t __spiTranslate24(uint32_t data, bool msb)
{
    if(msb) {
        union {
            uint32_t l;
            uint8_t b[4];
        } out;
        out.l = data;
        return out.b[2] | (out.b[1] << 8) | (out.b[0] << 16);
    } else {
        return data;
    }
}

uint32_t __spiTranslate32(uint32_t data, bool msb)
{
    if(msb) {
        union {
            uint32_t l;
            uint8_t b[4];
        } out;
        out.l = data;
        return out.b[3] | (out.b[2] << 8) | (out.b[1] << 16) | (out.b[0] << 24);
    } else {
        return data;
    }
}

void spiWriteWord(spi_t * spi, uint16_t data)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = 15;
    spi->dev->miso_dlen.usr_miso_dbitlen = 15;
    spi->dev->data_buf[0] = __spiTranslate16(data, !spi->dev->ctrl.wr_bit_order);
    spi->dev->cmd.usr = 1;
    SPI_MUTEX_UNLOCK();
}

uint16_t spiReadWord(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    uint16_t data;
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    data = __spiTranslate16(spi->dev->data_buf[0] & 0xFFFF, !spi->dev->ctrl.rd_bit_order);
    SPI_MUTEX_UNLOCK();
    return data;
}

void spiWriteLong(spi_t * spi, uint32_t data)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = 31;
    spi->dev->miso_dlen.usr_miso_dbitlen = 31;
    spi->dev->data_buf[0] = __spiTranslate32(data, !spi->dev->ctrl.wr_bit_order);
    spi->dev->cmd.usr = 1;
    SPI_MUTEX_UNLOCK();
}

uint32_t spiReadLong(spi_t * spi)
{
    if(!spi) {
        return 0;
    }
    uint32_t data;
    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    data = __spiTranslate32(spi->dev->data_buf[0], !spi->dev->ctrl.rd_bit_order);
    SPI_MUTEX_UNLOCK();
    return data;
}

void spiTransferBits(spi_t * spi, uint32_t data, uint32_t * out, uint8_t bits)
{
    if(!spi) {
        return;
    }

    if(bits > 32) {
        bits = 32;
    }
    uint32_t bytes = (bits + 7) / 8;//64 max
    uint32_t mask = (((uint64_t)1 << bits) - 1) & 0xFFFFFFFF;

    SPI_MUTEX_LOCK();
    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = (bits - 1);
    spi->dev->miso_dlen.usr_miso_dbitlen = (bits - 1);
    if(bytes == 1) {
        spi->dev->data_buf[0] = data & mask;
    } else if(bytes == 2) {
        spi->dev->data_buf[0] = __spiTranslate16(data & mask, !spi->dev->ctrl.wr_bit_order);
    } else if(bytes == 3) {
        spi->dev->data_buf[0] = __spiTranslate24(data & mask, !spi->dev->ctrl.wr_bit_order);
    } else {
        spi->dev->data_buf[0] = __spiTranslate32(data & mask, !spi->dev->ctrl.wr_bit_order);
    }
    spi->dev->cmd.usr = 1;

    if(out) {
        while(spi->dev->cmd.usr);
        if(bytes == 1) {
            *out = spi->dev->data_buf[0] & mask;
        } else if(bytes == 2) {
            *out = __spiTranslate16(spi->dev->data_buf[0] & mask, !spi->dev->ctrl.wr_bit_order);
        } else if(bytes == 3) {
            *out = __spiTranslate24(spi->dev->data_buf[0] & mask, !spi->dev->ctrl.wr_bit_order);
        } else {
            *out = __spiTranslate32(spi->dev->data_buf[0] & mask, !spi->dev->ctrl.wr_bit_order);
        }
    }
    SPI_MUTEX_UNLOCK();
}

void __spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t bytes)
{
    if(!spi) {
        return;
    }
    int i;

    if(bytes > 64) {
        bytes = 64;
    }

    uint32_t words = (bytes + 3) / 4;//16 max

    uint32_t wordsBuf[16] = {0,};
    uint8_t * bytesBuf = (uint8_t *) wordsBuf;

    if(data) {
        memcpy(bytesBuf, data, bytes);//copy data to buffer
    } else {
        memset(bytesBuf, 0xFF, bytes);
    }

    while(spi->dev->cmd.usr);
    spi->dev->mosi_dlen.usr_mosi_dbitlen = ((bytes * 8) - 1);
    spi->dev->miso_dlen.usr_miso_dbitlen = ((bytes * 8) - 1);

    for(i=0; i<words; i++) {
        spi->dev->data_buf[i] = wordsBuf[i];    //copy buffer to spi fifo
    }

    spi->dev->cmd.usr = 1;

    if(out) {
        while(spi->dev->cmd.usr);
        for(i=0; i<words; i++) {
            wordsBuf[i] = spi->dev->data_buf[i];//copy spi fifo to buffer
        }
        memcpy(out, bytesBuf, bytes);//copy buffer to output
    }
}

void spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t size)
{
    if(!spi) {
        return;
    }
    SPI_MUTEX_LOCK();
    while(size) {
        if(size > 64) {
            __spiTransferBytes(spi, data, out, 64);
            size -= 64;
            if(data) {
                data += 64;
            }
            if(out) {
                out += 64;
            }
        } else {
            __spiTransferBytes(spi, data, out, size);
            size = 0;
        }
    }
    SPI_MUTEX_UNLOCK();
}


typedef union {
    uint32_t regValue;
    struct {
        unsigned regL :6;
        unsigned regH :6;
        unsigned regN :6;
        unsigned regPre :13;
        unsigned regEQU :1;
    };
} spiClk_t;

#define ClkRegToFreq(reg) (CPU_CLK_FREQ / (((reg)->regPre + 1) * ((reg)->regN + 1)))

uint32_t spiClockDivToFrequency(uint32_t clockDiv)
{
    spiClk_t reg = { clockDiv };
    return ClkRegToFreq(&reg);
}

uint32_t spiFrequencyToClockDiv(uint32_t freq)
{

    if(freq >= CPU_CLK_FREQ) {
        return SPI_CLK_EQU_SYSCLK;
    }

    const spiClk_t minFreqReg = { 0x7FFFF000 };
    uint32_t minFreq = ClkRegToFreq((spiClk_t*) &minFreqReg);
    if(freq < minFreq) {
        return minFreqReg.regValue;
    }

    uint8_t calN = 1;
    spiClk_t bestReg = { 0 };
    int32_t bestFreq = 0;

    while(calN <= 0x3F) {
        spiClk_t reg = { 0 };
        int32_t calFreq;
        int32_t calPre;
        int8_t calPreVari = -2;

        reg.regN = calN;

        while(calPreVari++ <= 1) {
            calPre = (((CPU_CLK_FREQ / (reg.regN + 1)) / freq) - 1) + calPreVari;
            if(calPre > 0x1FFF) {
                reg.regPre = 0x1FFF;
            } else if(calPre <= 0) {
                reg.regPre = 0;
            } else {
                reg.regPre = calPre;
            }
            reg.regL = ((reg.regN + 1) / 2);
            calFreq = ClkRegToFreq(&reg);
            if(calFreq == (int32_t) freq) {
                memcpy(&bestReg, &reg, sizeof(bestReg));
                break;
            } else if(calFreq < (int32_t) freq) {
                if(abs(freq - calFreq) < abs(freq - bestFreq)) {
                    bestFreq = calFreq;
                    memcpy(&bestReg, &reg, sizeof(bestReg));
                }
            }
        }
        if(calFreq == (int32_t) freq) {
            break;
        }
        calN++;
    }
    return bestReg.regValue;
}