esp-idf/components/freemodbus/serial_master/modbus_controller/mbc_serial_master.c

/*
 * SPDX-FileCopyrightText: 2016-2022 Espressif Systems (Shanghai) CO LTD
 *
 * SPDX-License-Identifier: Apache-2.0
 */

// mbc_serial_master.c
// Serial master implementation of the  Modbus controller

#include <sys/time.h>               // for calculation of time stamp in milliseconds
#include "esp_log.h"                // for log_write
#include <string.h>                 // for memcpy
#include "freertos/FreeRTOS.h"      // for task creation and queue access
#include "freertos/task.h"          // for task api access
#include "freertos/event_groups.h"  // for event groups
#include "freertos/queue.h"         // for queue api access
#include "mb_m.h"                   // for modbus stack master types definition
#include "port.h"                   // for port callback functions
#include "mbutils.h"                // for mbutils functions definition for stack callback
#include "sdkconfig.h"              // for KConfig values
#include "esp_modbus_common.h"      // for common types
#include "esp_modbus_master.h"      // for public master types
#include "mbc_master.h"             // for private master types
#include "mbc_serial_master.h"      // for serial master create function and types

// The Modbus Transmit Poll function defined in port
extern BOOL xMBMasterPortSerialTxPoll(void);

/*-----------------------Master mode use these variables----------------------*/
#define MB_RESPONSE_TICS pdMS_TO_TICKS(CONFIG_FMB_MASTER_TIMEOUT_MS_RESPOND + 10)


static mb_master_interface_t* mbm_interface_ptr = NULL; //&default_interface_inst;
static const char *TAG = "MB_CONTROLLER_MASTER";

// Modbus event processing task
static void modbus_master_task(void *pvParameters)
{
    // The interface must be initialized before start of state machine
    MB_MASTER_ASSERT(mbm_interface_ptr != NULL);
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    // Main Modbus stack processing cycle
    for (;;) {
        // Wait for poll events
        BaseType_t status = xEventGroupWaitBits(mbm_opts->mbm_event_group,
                                                (BaseType_t)(MB_EVENT_STACK_STARTED),
                                                pdFALSE, // do not clear bits
                                                pdFALSE,
                                                portMAX_DELAY);
        // Check if stack started then poll for data
        if (status & MB_EVENT_STACK_STARTED) {
            (void)eMBMasterPoll(); // Allow stack to process data
            // Send response buffer if ready to be sent
            BOOL xSentState = xMBMasterPortSerialTxPoll();
            if (xSentState) {
                // Let state machine know that request frame was transmitted out
                (void)xMBMasterPortEventPost(EV_MASTER_FRAME_SENT);
            }
        }
    }
}

// Setup Modbus controller parameters
static esp_err_t mbc_serial_master_setup(void* comm_info)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;

    const mb_master_comm_info_t* comm_info_ptr = (mb_master_comm_info_t*)comm_info;
    // Check communication options
    MB_MASTER_CHECK(((comm_info_ptr->mode == MB_MODE_RTU) || (comm_info_ptr->mode == MB_MODE_ASCII)),
                ESP_ERR_INVALID_ARG, "mb incorrect mode = (0x%x).",
                (uint32_t)comm_info_ptr->mode);
    MB_MASTER_CHECK((comm_info_ptr->port <= UART_NUM_MAX), ESP_ERR_INVALID_ARG,
                "mb wrong port to set = (0x%x).", (uint32_t)comm_info_ptr->port);
    MB_MASTER_CHECK((comm_info_ptr->parity <= UART_PARITY_ODD), ESP_ERR_INVALID_ARG,
                "mb wrong parity option = (0x%x).", (uint32_t)comm_info_ptr->parity);
    // Save the communication options
    mbm_opts->mbm_comm = *(mb_communication_info_t*)comm_info_ptr;
    return ESP_OK;
}

// Modbus controller stack start function
static esp_err_t mbc_serial_master_start(void)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    eMBErrorCode status = MB_EIO;
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    const mb_communication_info_t* comm_info = (mb_communication_info_t*)&mbm_opts->mbm_comm;

    // Initialize Modbus stack using mbcontroller parameters
    status = eMBMasterSerialInit((eMBMode)comm_info->mode, (UCHAR)comm_info->port,
                                    (ULONG)comm_info->baudrate,
                                    MB_PORT_PARITY_GET(comm_info->parity));

    MB_MASTER_CHECK((status == MB_ENOERR), ESP_ERR_INVALID_STATE,
            "mb stack initialization failure, eMBInit() returns (0x%x).", status);
    status = eMBMasterEnable();
    MB_MASTER_CHECK((status == MB_ENOERR), ESP_ERR_INVALID_STATE,
            "mb stack set slave ID failure, eMBEnable() returned (0x%x).", (uint32_t)status);
    // Set the mbcontroller start flag
    EventBits_t flag = xEventGroupSetBits(mbm_opts->mbm_event_group,
                                            (EventBits_t)MB_EVENT_STACK_STARTED);
    MB_MASTER_CHECK((flag & MB_EVENT_STACK_STARTED),
                ESP_ERR_INVALID_STATE, "mb stack start event set error.");
    return ESP_OK;
}

// Modbus controller destroy function
static esp_err_t mbc_serial_master_destroy(void)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    eMBErrorCode mb_error = MB_ENOERR;
    // Stop polling by clearing correspondent bit in the event group
    EventBits_t flag = xEventGroupClearBits(mbm_opts->mbm_event_group,
                                    (EventBits_t)MB_EVENT_STACK_STARTED);
    MB_MASTER_CHECK((flag & MB_EVENT_STACK_STARTED),
                ESP_ERR_INVALID_STATE, "mb stack stop event failure.");
    // Desable and then destroy the Modbus stack
    mb_error = eMBMasterDisable();
    MB_MASTER_CHECK((mb_error == MB_ENOERR), ESP_ERR_INVALID_STATE, "mb stack disable failure.");
    (void)vTaskDelete(mbm_opts->mbm_task_handle);
    (void)vEventGroupDelete(mbm_opts->mbm_event_group);
    mb_error = eMBMasterClose();
    MB_MASTER_CHECK((mb_error == MB_ENOERR), ESP_ERR_INVALID_STATE,
            "mb stack close failure returned (0x%x).", (uint32_t)mb_error);
    free(mbm_interface_ptr); // free the memory allocated for options
    vMBPortSetMode((UCHAR)MB_PORT_INACTIVE);
    mbm_interface_ptr = NULL;
    return ESP_OK;
}

// Set Modbus parameter description table
static esp_err_t mbc_serial_master_set_descriptor(const mb_parameter_descriptor_t* descriptor, const uint16_t num_elements)
{
    MB_MASTER_CHECK((descriptor != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect descriptor.");
    MB_MASTER_CHECK((num_elements >= 1),
                        ESP_ERR_INVALID_ARG, "mb table size is incorrect.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    const mb_parameter_descriptor_t *reg_ptr = descriptor;
    // Go through all items in the table to check all Modbus registers
    for (uint16_t counter = 0; counter < (num_elements); counter++, reg_ptr++)
    {
        // Below is the code to check consistency of the table format and required fields.
        MB_MASTER_CHECK((reg_ptr->cid == counter),
                            ESP_ERR_INVALID_ARG, "mb descriptor cid field is incorrect.");
        MB_MASTER_CHECK((reg_ptr->param_key != NULL),
                            ESP_ERR_INVALID_ARG, "mb descriptor param key is incorrect.");
        MB_MASTER_CHECK((reg_ptr->mb_size > 0),
                            ESP_ERR_INVALID_ARG, "mb descriptor param size is incorrect.");
    }
    mbm_opts->mbm_param_descriptor_table = descriptor;
    mbm_opts->mbm_param_descriptor_size = num_elements;
    return ESP_OK;
}

// Send custom Modbus request defined as mb_param_request_t structure
static esp_err_t mbc_serial_master_send_request(mb_param_request_t* request, void* data_ptr)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    MB_MASTER_CHECK((request != NULL),
                    ESP_ERR_INVALID_ARG, "mb request structure.");
    MB_MASTER_CHECK((data_ptr != NULL),
                    ESP_ERR_INVALID_ARG, "mb incorrect data pointer.");

    eMBMasterReqErrCode mb_error = MB_MRE_NO_REG;
    esp_err_t error = ESP_FAIL;

    uint8_t mb_slave_addr = request->slave_addr;
    uint8_t mb_command = request->command;
    uint16_t mb_offset = request->reg_start;
    uint16_t mb_size = request->reg_size;

    // Set the buffer for callback function processing of received data
    mbm_opts->mbm_reg_buffer_ptr = (uint8_t*)data_ptr;
    mbm_opts->mbm_reg_buffer_size = mb_size;

    // Calls appropriate request function to send request and waits response
    switch(mb_command)
    {
        case MB_FUNC_READ_COILS:
            mb_error = eMBMasterReqReadCoils((UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                               (USHORT)mb_size , (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_WRITE_SINGLE_COIL:
            mb_error = eMBMasterReqWriteCoil((UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                *(USHORT*)data_ptr, (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_WRITE_MULTIPLE_COILS:
            mb_error = eMBMasterReqWriteMultipleCoils((UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                            (USHORT)mb_size, (UCHAR*)data_ptr, (LONG)MB_RESPONSE_TICS);
            break;
        case MB_FUNC_READ_DISCRETE_INPUTS:
            mb_error = eMBMasterReqReadDiscreteInputs((UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                        (USHORT)mb_size, (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_READ_HOLDING_REGISTER:
            mb_error = eMBMasterReqReadHoldingRegister((UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                            (USHORT)mb_size, (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_WRITE_REGISTER:
            mb_error = eMBMasterReqWriteHoldingRegister( (UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                            *(USHORT*)data_ptr, (LONG)MB_RESPONSE_TICS );
            break;

        case MB_FUNC_WRITE_MULTIPLE_REGISTERS:
            mb_error = eMBMasterReqWriteMultipleHoldingRegister( (UCHAR)mb_slave_addr,
                                                                    (USHORT)mb_offset, (USHORT)mb_size,
                                                                    (USHORT*)data_ptr, (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_READWRITE_MULTIPLE_REGISTERS:
            mb_error = eMBMasterReqReadWriteMultipleHoldingRegister( (UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                                       (USHORT)mb_size, (USHORT*)data_ptr,
                                                                       (USHORT)mb_offset, (USHORT)mb_size,
                                                                       (LONG)MB_RESPONSE_TICS );
            break;
        case MB_FUNC_READ_INPUT_REGISTER:
            mb_error = eMBMasterReqReadInputRegister( (UCHAR)mb_slave_addr, (USHORT)mb_offset,
                                                        (USHORT)mb_size, (LONG) MB_RESPONSE_TICS );
            break;
        default:
            ESP_LOGE(TAG, "%s: Incorrect function in request (%u) ",
                                                    __FUNCTION__, mb_command);
            mb_error = MB_MRE_NO_REG;
            break;
    }

    // Propagate the Modbus errors to higher level
    switch(mb_error)
    {
        case MB_MRE_NO_ERR:
            error = ESP_OK;
            break;

        case MB_MRE_NO_REG:
            error = ESP_ERR_NOT_SUPPORTED; // Invalid register request
            break;

        case MB_MRE_TIMEDOUT:
            error = ESP_ERR_TIMEOUT; // Slave did not send response
            break;

        case MB_MRE_EXE_FUN:
        case MB_MRE_REV_DATA:
            error = ESP_ERR_INVALID_RESPONSE; // Invalid response from slave
            break;

        case MB_MRE_MASTER_BUSY:
            error = ESP_ERR_INVALID_STATE; // Master is busy (previous request is pending)
            break;

        default:
            ESP_LOGE(TAG, "%s: Incorrect return code (%x) ",
                                                                __FUNCTION__, mb_error);
            error = ESP_FAIL;
            break;
    }

    return error;
}

static esp_err_t mbc_serial_master_get_cid_info(uint16_t cid, const mb_parameter_descriptor_t** param_buffer)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;

    MB_MASTER_CHECK((param_buffer != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect data buffer pointer.");
    MB_MASTER_CHECK((mbm_opts->mbm_param_descriptor_table != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect descriptor table or not set.");
    MB_MASTER_CHECK((cid < mbm_opts->mbm_param_descriptor_size),
                        ESP_ERR_NOT_FOUND, "mb incorrect cid of characteristic.");

    // It is assumed that characteristics cid increased in the table
    const mb_parameter_descriptor_t* reg_info = &mbm_opts->mbm_param_descriptor_table[cid];

    MB_MASTER_CHECK((reg_info->param_key != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect characteristic key.");
    *param_buffer = reg_info;
    return ESP_OK;
}

// Helper function to get modbus command for each type of Modbus register area
static uint8_t mbc_serial_master_get_command(mb_param_type_t param_type, mb_param_mode_t mode)
{
    uint8_t command = 0;
    switch(param_type)
    { //
        case MB_PARAM_HOLDING:
            command = (mode == MB_PARAM_WRITE) ?
                        MB_FUNC_WRITE_MULTIPLE_REGISTERS :
                        MB_FUNC_READ_HOLDING_REGISTER;
            break;
        case MB_PARAM_INPUT:
            command = MB_FUNC_READ_INPUT_REGISTER;
            break;
        case MB_PARAM_COIL:
            command = (mode == MB_PARAM_WRITE) ?
                        MB_FUNC_WRITE_MULTIPLE_COILS :
                        MB_FUNC_READ_COILS;
            break;
        case MB_PARAM_DISCRETE:
            if (mode != MB_PARAM_WRITE) {
                command = MB_FUNC_READ_DISCRETE_INPUTS;
            } else {
                ESP_LOGE(TAG, "%s: Incorrect mode (%u)",
                            __FUNCTION__, (uint8_t)mode);
            }
            break;
        default:
            ESP_LOGE(TAG, "%s: Incorrect param type (%u)",
                            __FUNCTION__, param_type);
            break;
    }
    return command;
}

// Helper to search parameter by name in the parameter description table
// and fills Modbus request fields accordingly
static esp_err_t mbc_serial_master_set_request(char* name, mb_param_mode_t mode,
                                                mb_param_request_t* request,
                                                mb_parameter_descriptor_t* reg_data)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    ESP_ERR_INVALID_STATE,
                    "Master interface uninitialized.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    esp_err_t error = ESP_ERR_NOT_FOUND;
    MB_MASTER_CHECK((name != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect parameter name.");
    MB_MASTER_CHECK((request != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect request parameter.");
    MB_MASTER_CHECK((mode <= MB_PARAM_WRITE),
                        ESP_ERR_INVALID_ARG, "mb incorrect mode.");
    MB_MASTER_ASSERT(mbm_opts->mbm_param_descriptor_table != NULL);
    const mb_parameter_descriptor_t* reg_ptr = mbm_opts->mbm_param_descriptor_table;
    for (uint16_t counter = 0; counter < (mbm_opts->mbm_param_descriptor_size); counter++, reg_ptr++)
    {
        // Check the cid of the parameter is equal to record number in the table
        // Check the length of name and parameter key strings from table
        size_t param_key_len = strlen((const char*)reg_ptr->param_key);
        if (param_key_len != strlen((const char*)name)) {
            continue; // The length of strings is different then check next record in the table
        }
        // Compare the name of parameter with parameter key from table
        int comp_result = memcmp((const void*)name, (const void*)reg_ptr->param_key, (size_t)param_key_len);
        if (comp_result == 0) {
            // The correct line is found in the table and reg_ptr points to the found parameter description
            request->slave_addr = reg_ptr->mb_slave_addr;
            request->reg_start = reg_ptr->mb_reg_start;
            request->reg_size = reg_ptr->mb_size;
            request->command = mbc_serial_master_get_command(reg_ptr->mb_param_type, mode);
            MB_MASTER_CHECK((request->command > 0),
                                ESP_ERR_INVALID_ARG,
                                "mb incorrect command or parameter type.");
            if (reg_data != NULL) {
                *reg_data = *reg_ptr; // Set the cid registered parameter data
            }
            error = ESP_OK;
            break;
        }
    }
    return error;
}

// Get parameter data for corresponding characteristic
static esp_err_t mbc_serial_master_get_parameter(uint16_t cid, char* name,
                                                    uint8_t* value_ptr, uint8_t *type)
{
    MB_MASTER_CHECK((name != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect descriptor.");
    MB_MASTER_CHECK((type != NULL),
                        ESP_ERR_INVALID_ARG, "type pointer is incorrect.");
    esp_err_t error = ESP_ERR_INVALID_RESPONSE;
    mb_param_request_t request ;
    mb_parameter_descriptor_t reg_info = { 0 };

    error = mbc_serial_master_set_request(name, MB_PARAM_READ, &request, &reg_info);
    if ((error == ESP_OK) && (cid == reg_info.cid)) {
        // Send request to read characteristic data
        error = mbc_serial_master_send_request(&request, value_ptr);
        if (error == ESP_OK) {
            ESP_LOGD(TAG, "%s: Good response for get cid(%u) = %s",
                                    __FUNCTION__, (int)reg_info.cid, (char*)esp_err_to_name(error));
        } else {
            ESP_LOGD(TAG, "%s: Bad response to get cid(%u) = %s",
                                            __FUNCTION__, reg_info.cid, (char*)esp_err_to_name(error));
        }
        // Set the type of parameter found in the table
        *type = reg_info.param_type;
    } else {
        ESP_LOGE(TAG, "%s: The cid(%u) not found in the data dictionary.",
                                                    __FUNCTION__, reg_info.cid);
        error = ESP_ERR_INVALID_ARG;
    }
    return error;
}

// Set parameter value for characteristic selected by name and cid
static esp_err_t mbc_serial_master_set_parameter(uint16_t cid, char* name,
                                                    uint8_t* value_ptr, uint8_t *type)
{
    MB_MASTER_CHECK((name != NULL),
                        ESP_ERR_INVALID_ARG, "mb incorrect descriptor.");
    MB_MASTER_CHECK((value_ptr != NULL),
                        ESP_ERR_INVALID_ARG, "value pointer is incorrect.");
    MB_MASTER_CHECK((type != NULL),
                        ESP_ERR_INVALID_ARG, "type pointer is incorrect.");
    esp_err_t error = ESP_ERR_INVALID_RESPONSE;
    mb_param_request_t request ;
    mb_parameter_descriptor_t reg_info = { 0 };

    error = mbc_serial_master_set_request(name, MB_PARAM_WRITE, &request, &reg_info);
    if ((error == ESP_OK) && (cid == reg_info.cid)) {
        // Send request to write characteristic data
        error = mbc_serial_master_send_request(&request, value_ptr);
        if (error == ESP_OK) {
            ESP_LOGD(TAG, "%s: Good response for set cid(%u) = %s",
                                    __FUNCTION__, (int)reg_info.cid, (char*)esp_err_to_name(error));
        } else {
            ESP_LOGD(TAG, "%s: Bad response to set cid(%u) = %s",
                                    __FUNCTION__, reg_info.cid, (char*)esp_err_to_name(error));
        }
        // Set the type of parameter found in the table
        *type = reg_info.param_type;
    } else {
        ESP_LOGE(TAG, "%s: The requested cid(%u) not found in the data dictionary.",
                                    __FUNCTION__, reg_info.cid);
        error = ESP_ERR_INVALID_ARG;
    }
    return error;
}

/* ----------------------- Callback functions for Modbus stack ---------------------------------*/
// These are executed by modbus stack to read appropriate type of registers.

/**
 * Modbus master input register callback function.
 *
 * @param pucRegBuffer input register buffer
 * @param usAddress input register address
 * @param usNRegs input register number
 *
 * @return result
 */
// Callback function for reading of MB Input Registers
eMBErrorCode eMBRegInputCBSerialMaster(UCHAR * pucRegBuffer, USHORT usAddress,
                                USHORT usNRegs)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    MB_EILLSTATE,
                    "Master interface uninitialized.");
    MB_MASTER_CHECK((pucRegBuffer != NULL), MB_EINVAL,
                    "Master stack processing error.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    // Number of input registers to be transferred
    USHORT usRegInputNregs = (USHORT)mbm_opts->mbm_reg_buffer_size;
    UCHAR* pucInputBuffer = (UCHAR*)mbm_opts->mbm_reg_buffer_ptr; // Get instance address
    USHORT usRegs = usNRegs;
    eMBErrorCode eStatus = MB_ENOERR;
    // If input or configuration parameters are incorrect then return an error to stack layer
    if ((pucInputBuffer != NULL)
            && (usNRegs >= 1)
            && (usRegInputNregs == usRegs)) {
        while (usRegs > 0) {
            _XFER_2_RD(pucInputBuffer, pucRegBuffer);
            usRegs -= 1;
        }
    } else {
        eStatus = MB_ENOREG;
    }
    return eStatus;
}

/**
 * Modbus master holding register callback function.
 *
 * @param pucRegBuffer holding register buffer
 * @param usAddress holding register address
 * @param usNRegs holding register number
 * @param eMode read or write
 *
 * @return result
 */
// Callback function for reading of MB Holding Registers
// Executed by stack when request to read/write holding registers is received
eMBErrorCode eMBRegHoldingCBSerialMaster(UCHAR * pucRegBuffer, USHORT usAddress,
        USHORT usNRegs, eMBRegisterMode eMode)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    MB_EILLSTATE,
                    "Master interface uninitialized.");
    MB_MASTER_CHECK((pucRegBuffer != NULL), MB_EINVAL,
                    "Master stack processing error.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    USHORT usRegHoldingNregs = (USHORT)mbm_opts->mbm_reg_buffer_size;
    UCHAR* pucHoldingBuffer = (UCHAR*)mbm_opts->mbm_reg_buffer_ptr;
    eMBErrorCode eStatus = MB_ENOERR;
    USHORT usRegs = usNRegs;
    // Check input and configuration parameters for correctness
    if ((pucHoldingBuffer != NULL)
            && (usRegHoldingNregs == usNRegs)
            && (usNRegs >= 1)) {
        switch (eMode) {
            case MB_REG_WRITE:
                while (usRegs > 0) {
                    _XFER_2_RD(pucRegBuffer, pucHoldingBuffer);
                    usRegs -= 1;
                };
                break;
            case MB_REG_READ:
                while (usRegs > 0) {
                    _XFER_2_WR(pucHoldingBuffer, pucRegBuffer);
                    pucHoldingBuffer += 2;
                    usRegs -= 1;
                };
                break;
        }
    } else {
        eStatus = MB_ENOREG;
    }
    return eStatus;
}

/**
 * Modbus master coils callback function.
 *
 * @param pucRegBuffer coils buffer
 * @param usAddress coils address
 * @param usNCoils coils number
 * @param eMode read or write
 *
 * @return result
 */
// Callback function for reading of MB Coils Registers
eMBErrorCode eMBRegCoilsCBSerialMaster(UCHAR* pucRegBuffer, USHORT usAddress,
        USHORT usNCoils, eMBRegisterMode eMode)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    MB_EILLSTATE, "Master interface uninitialized.");
    MB_MASTER_CHECK((pucRegBuffer != NULL),
                    MB_EINVAL, "Master stack processing error.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    USHORT usRegCoilNregs = (USHORT)mbm_opts->mbm_reg_buffer_size;
    UCHAR* pucRegCoilsBuf = (UCHAR*)mbm_opts->mbm_reg_buffer_ptr;
    eMBErrorCode eStatus = MB_ENOERR;
    USHORT iRegIndex;
    USHORT usCoils = usNCoils;
    usAddress--; // The address is already + 1
    if ((usRegCoilNregs >= 1)
            && (pucRegCoilsBuf != NULL)
            && (usNCoils == usRegCoilNregs)) {
        iRegIndex = (usAddress % 8);
        switch (eMode) {
            case MB_REG_WRITE:
                while (usCoils > 0) {
                    UCHAR ucResult = xMBUtilGetBits((UCHAR*)pucRegCoilsBuf, iRegIndex, 1);
                    xMBUtilSetBits(pucRegBuffer, iRegIndex - (usAddress % 8) , 1, ucResult);
                    iRegIndex++;
                    usCoils--;
                }
                break;
            case MB_REG_READ:
                while (usCoils > 0) {
                    UCHAR ucResult = xMBUtilGetBits(pucRegBuffer, iRegIndex - (usAddress % 8), 1);
                    xMBUtilSetBits((uint8_t*)pucRegCoilsBuf, iRegIndex, 1, ucResult);
                    iRegIndex++;
                    usCoils--;
                }
                break;
        } // switch ( eMode )
    } else {
        // If the configuration or input parameters are incorrect then return error to stack
        eStatus = MB_ENOREG;
    }
    return eStatus;
}

/**
 * Modbus master discrete callback function.
 *
 * @param pucRegBuffer discrete buffer
 * @param usAddress discrete address
 * @param usNDiscrete discrete number
 *
 * @return result
 */
// Callback function for reading of MB Discrete Input Registers
eMBErrorCode eMBRegDiscreteCBSerialMaster(UCHAR * pucRegBuffer, USHORT usAddress,
                            USHORT usNDiscrete)
{
    MB_MASTER_CHECK((mbm_interface_ptr != NULL),
                    MB_EILLSTATE, "Master interface uninitialized.");
    MB_MASTER_CHECK((pucRegBuffer != NULL),
                    MB_EINVAL, "Master stack processing error.");
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    USHORT usRegDiscreteNregs = (USHORT)mbm_opts->mbm_reg_buffer_size;
    UCHAR* pucRegDiscreteBuf = (UCHAR*)mbm_opts->mbm_reg_buffer_ptr;
    eMBErrorCode eStatus = MB_ENOERR;
    USHORT iRegBitIndex, iNReg;
    UCHAR* pucDiscreteInputBuf;
    iNReg = usNDiscrete / 8 + 1;
    pucDiscreteInputBuf = (UCHAR*) pucRegDiscreteBuf;
    // It is already plus one in Modbus function method.
    usAddress--;
    if ((usRegDiscreteNregs >= 1)
            && (pucRegDiscreteBuf != NULL)
            && (usNDiscrete >= 1)) {
        iRegBitIndex = (USHORT)(usAddress) % 8; // Get bit index
        while (iNReg > 1)
        {
            xMBUtilSetBits(pucDiscreteInputBuf++, iRegBitIndex, 8, *pucRegBuffer++);
            iNReg--;
        }
        // last discrete
        usNDiscrete = usNDiscrete % 8;
        // xMBUtilSetBits has bug when ucNBits is zero
        if (usNDiscrete != 0)
        {
            xMBUtilSetBits(pucDiscreteInputBuf, iRegBitIndex, usNDiscrete, *pucRegBuffer++);
        }
    } else {
        eStatus = MB_ENOREG;
    }
    return eStatus;
}

// Initialization of resources for Modbus serial master controller
esp_err_t mbc_serial_master_create(void** handler)
{
    // Allocate space for master interface structure
    if (mbm_interface_ptr == NULL) {
        mbm_interface_ptr = malloc(sizeof(mb_master_interface_t));
    }
    MB_MASTER_ASSERT(mbm_interface_ptr != NULL);

    // Initialize interface properties
    mb_master_options_t* mbm_opts = &mbm_interface_ptr->opts;
    mbm_opts->port_type = MB_PORT_SERIAL_MASTER;

    vMBPortSetMode((UCHAR)MB_PORT_SERIAL_MASTER);

    mbm_opts->mbm_comm.mode = MB_MODE_RTU;
    mbm_opts->mbm_comm.port = MB_UART_PORT;
    mbm_opts->mbm_comm.baudrate = MB_DEVICE_SPEED;
    mbm_opts->mbm_comm.parity = MB_PARITY_NONE;

    // Initialization of active context of the modbus controller
    BaseType_t status = 0;
    // Parameter change notification queue
    mbm_opts->mbm_event_group = xEventGroupCreate();
    MB_MASTER_CHECK((mbm_opts->mbm_event_group != NULL),
                        ESP_ERR_NO_MEM, "mb event group error.");
    // Create modbus controller task
    status = xTaskCreatePinnedToCore((void*)&modbus_master_task,
                            "modbus_matask",
                            MB_CONTROLLER_STACK_SIZE,
                            NULL,                       // No parameters
                            MB_CONTROLLER_PRIORITY,
                            &mbm_opts->mbm_task_handle,
                            MB_PORT_TASK_AFFINITY);
    if (status != pdPASS) {
        vTaskDelete(mbm_opts->mbm_task_handle);
        MB_MASTER_CHECK((status == pdPASS), ESP_ERR_NO_MEM,
                "mb controller task creation error, xTaskCreate() returns (0x%x).",
                (uint32_t)status);
    }
    MB_MASTER_ASSERT(mbm_opts->mbm_task_handle != NULL); // The task is created but handle is incorrect

    // Initialize public interface methods of the interface
    mbm_interface_ptr->init = mbc_serial_master_create;
    mbm_interface_ptr->destroy = mbc_serial_master_destroy;
    mbm_interface_ptr->setup = mbc_serial_master_setup;
    mbm_interface_ptr->start = mbc_serial_master_start;
    mbm_interface_ptr->get_cid_info = mbc_serial_master_get_cid_info;
    mbm_interface_ptr->get_parameter = mbc_serial_master_get_parameter;
    mbm_interface_ptr->send_request = mbc_serial_master_send_request;
    mbm_interface_ptr->set_descriptor = mbc_serial_master_set_descriptor;
    mbm_interface_ptr->set_parameter = mbc_serial_master_set_parameter;

    mbm_interface_ptr->master_reg_cb_discrete = eMBRegDiscreteCBSerialMaster;
    mbm_interface_ptr->master_reg_cb_input = eMBRegInputCBSerialMaster;
    mbm_interface_ptr->master_reg_cb_holding = eMBRegHoldingCBSerialMaster;
    mbm_interface_ptr->master_reg_cb_coils = eMBRegCoilsCBSerialMaster;

    *handler = mbm_interface_ptr;

    return ESP_OK;
}