void foo() {
    ENTER_CRITICAL_SECTION(); // второе попадание в критическую секцию

    // делаем полезные штуки не боясь прерываний

    EXIT_CRITICAL_SECTION(); // тут плохо, прерывания не должны включаться, мы все еще в критической секции функции bar()
}

void bar() {
    ENTER_CRITICAL_SECTION(); // первое попадание в критическую секцию

    foo(); // после выполнения функции прерывания уже работают, а это неправильно

    EXIT_CRITICAL_SECTION(); // бесполезно =(
}

/*
 * FreeModbus Libary: BARE Port
 * Copyright (C) 2006 Christian Walter <wolti@sil.at>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * File: $Id: port.h,v 1.1 2006/08/22 21:35:13 wolti Exp $
 */

#ifndef _PORT_H
#define _PORT_H

#include "stm32f3xx_hal.h"
#include <inttypes.h>

#define	INLINE                      inline
#define PR_BEGIN_EXTERN_C           extern "C" {
#define	PR_END_EXTERN_C             }

// управление прерываниями
#define ENTER_CRITICAL_SECTION( )	__disable_irq()
#define EXIT_CRITICAL_SECTION( )	__enable_irq()

// подменим вызовы по всей библиотеки
#define assert(val) assert_param(val)

typedef uint8_t BOOL;

typedef unsigned char UCHAR;
typedef char CHAR;

typedef uint16_t USHORT;
typedef int16_t SHORT;

typedef uint32_t ULONG;
typedef int32_t LONG;

#ifndef TRUE
#define TRUE            1
#endif

#ifndef FALSE
#define FALSE           0
#endif

// callback для uart
BOOL UART_IRQ_Handler(USART_TypeDef * usart);

#endif

/*
 * FreeModbus Libary: BARE Port
 * Copyright (C) 2006 Christian Walter <wolti@sil.at>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * File: $Id: porttimer.c,v 1.1 2006/08/22 21:35:13 wolti Exp $
 */

/* ----------------------- Platform includes --------------------------------*/
#include "port.h"
#include "stm32f3xx_hal_tim.h"

/* ----------------------- Modbus includes ----------------------------------*/
#include "mb.h"
#include "mbport.h"

/* ----------------------- static functions ---------------------------------*/
static void prvvTIMERExpiredISR( void );
static TIM_HandleTypeDef htim;

static uint16_t timeout = 0;
static uint16_t downcounter = 0;

/* ----------------------- Start implementation -----------------------------*/
BOOL
xMBPortTimersInit( USHORT usTim1Timerout50us )
{
	htim.Instance = TIM6;
	htim.Init.CounterMode = TIM_COUNTERMODE_UP;
	htim.Init.Prescaler = (HAL_RCC_GetPCLK1Freq() / 1000000) - 1;
	htim.Init.Period = 50 - 1;

	timeout = usTim1Timerout50us;

    return HAL_OK == HAL_TIM_Base_Init(&htim) ? TRUE : FALSE;
}

inline void
vMBPortTimersEnable(  )
{
    /* Enable the timer with the timeout passed to xMBPortTimersInit( ) */
	downcounter = timeout;
	HAL_TIM_Base_Start_IT(&htim);
}

inline void
vMBPortTimersDisable(  )
{
    /* Disable any pending timers. */
	HAL_TIM_Base_Stop_IT(&htim);
}

/* Create an ISR which is called whenever the timer has expired. This function
 * must then call pxMBPortCBTimerExpired( ) to notify the protocol stack that
 * the timer has expired.
 */
static void prvvTIMERExpiredISR( void )
{
    ( void )pxMBPortCBTimerExpired(  );
}

void TIM6_DAC1_IRQHandler(void) {
	/* TIM Update event */
	if(__HAL_TIM_GET_FLAG(&htim, TIM_FLAG_UPDATE) != RESET && __HAL_TIM_GET_IT_SOURCE(&htim, TIM_IT_UPDATE) !=RESET) {
		__HAL_TIM_CLEAR_IT(&htim, TIM_IT_UPDATE);
		if (!--downcounter)
			prvvTIMERExpiredISR();
	}
}

    huart.Init.Mode = UART_MODE_TX_RX; // работаем на прием и передачу
    huart.Init.HwFlowCtl = UART_HWCONTROL_NONE; // без контроля потока (у нас же rs485)
    // сэмплинг, не могу нормально объяснить, но это нужно для защиты от шумов
    huart.Init.OneBitSampling = UART_ONEBIT_SAMPLING_DISABLED;
    huart.Init.OverSampling = UART_OVERSAMPLING_16;
    // один стоп-бит
    huart.Init.StopBits = UART_STOPBITS_1;
    // без доп-фич
    huart.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;

    // портозависимая инициализация: UART, ножка контроля направления приемопередачи
    switch (ucPORT) {
    case 0:
        huart.Instance = USART1;
        DE_Port = GPIOA;
        DE_Pin = GPIO_PIN_12;
            break;
    case 1:
        huart.Instance = USART2;
        DE_Port = GPIOA;
        DE_Pin = GPIO_PIN_1;
            break;
    case 2:
        huart.Instance = USART3;
        DE_Port = GPIOB;
        DE_Pin = GPIO_PIN_14;
            break;
    default:
        // вызовем ошибку, если выбрали не тот номер порта, хотя это будет ошибкой портирования, но хоть что-то
        return FALSE;
    }

    // скорость
    huart.Init.BaudRate = ulBaudRate;

    // размер слова
    switch (ucDataBits) {
    case 8:
        huart.Init.WordLength = UART_WORDLENGTH_8B;
        break;
    case 9:
        huart.Init.WordLength = UART_WORDLENGTH_9B;
        break;
    default:
        // вызовем ошибку, если выбрали не тот номер порта, хотя это будет ошибкой портирования, но хоть что-то
        return FALSE;
    }

    // настраиваем бит четности
    switch (eParity) {
    case MB_PAR_NONE:
        huart.Init.Parity = UART_PARITY_NONE;
        break;
    case MB_PAR_EVEN:
        huart.Init.Parity = UART_PARITY_EVEN;
        break;
    case MB_PAR_ODD:
        huart.Init.Parity = UART_PARITY_ODD;
        break;
    default:
        // вызовем ошибку, если выбрали не тот номер порта, хотя это будет ошибкой портирования, но хоть что-то
        return FALSE;
    }

    // Инициализируем порт, как rs485
    return HAL_OK == HAL_RS485Ex_Init(&huart, UART_DE_POLARITY_HIGH, 0, 0) ? TRUE : FALSE;

/*
 * FreeModbus Libary: BARE Port
 * Copyright (C) 2006 Christian Walter <wolti@sil.at>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * File: $Id: portserial.c,v 1.1 2006/08/22 21:35:13 wolti Exp $
 */

#include "port.h"

/* ----------------------- Modbus includes ----------------------------------*/
#include "mb.h"
#include "mbport.h"

/* ----------------------- static functions ---------------------------------*/
static UART_HandleTypeDef huart;
static GPIO_TypeDef * DE_Port;
static uint16_t DE_Pin;
/* ----------------------- Start implementation -----------------------------*/
void
vMBPortSerialEnable( BOOL xRxEnable, BOOL xTxEnable )
{
    /* If xRXEnable enable serial receive interrupts. If xTxENable enable
     * transmitter empty interrupts.
     */
	if (xRxEnable) {
		HAL_GPIO_WritePin(DE_Port, DE_Pin, GPIO_PIN_RESET);
		__HAL_UART_ENABLE_IT(&huart, UART_IT_RXNE);
	} else {
		__HAL_UART_DISABLE_IT(&huart, UART_IT_RXNE);
	}

	if (xTxEnable) {
		HAL_GPIO_WritePin(DE_Port, DE_Pin, GPIO_PIN_SET);
		__HAL_UART_ENABLE_IT(&huart, UART_IT_TXE);
	} else {
		__HAL_UART_DISABLE_IT(&huart, UART_IT_TXE);
	}
}

BOOL
xMBPortSerialInit( UCHAR ucPORT, ULONG ulBaudRate, UCHAR ucDataBits, eMBParity eParity )
{
	huart.Init.Mode = UART_MODE_TX_RX;
	huart.Init.HwFlowCtl = UART_HWCONTROL_NONE;
	huart.Init.OneBitSampling = UART_ONEBIT_SAMPLING_DISABLED;
	huart.Init.OverSampling = UART_OVERSAMPLING_16;
	huart.Init.StopBits = UART_STOPBITS_1;
	huart.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;

	switch (ucPORT) {
	case 0:
		huart.Instance = USART1;
		DE_Port = GPIOA;
		DE_Pin = GPIO_PIN_4;
		break;
	case 1:
		huart.Instance = USART2;
		DE_Port = GPIOA;
		DE_Pin = GPIO_PIN_1;
		break;
	case 2:
		huart.Instance = USART3;
		DE_Port = GPIOB;
		DE_Pin = GPIO_PIN_14;
		break;
	default:
		return FALSE;
	}

	huart.Init.BaudRate = ulBaudRate;

	switch (ucDataBits) {
		case 8:
			huart.Init.WordLength = UART_WORDLENGTH_8B;
			break;
		case 9:
			huart.Init.WordLength = UART_WORDLENGTH_9B;
			break;
		default:
			return FALSE;
	}

	switch (eParity) {
	case MB_PAR_NONE:
		huart.Init.Parity = UART_PARITY_NONE;
		break;
	case MB_PAR_EVEN:
		huart.Init.Parity = UART_PARITY_EVEN;
		break;
	case MB_PAR_ODD:
		huart.Init.Parity = UART_PARITY_ODD;
		break;
	default:
		return FALSE;
	}

    return HAL_OK == HAL_RS485Ex_Init(&huart, UART_DE_POLARITY_HIGH, 0, 0);
}

BOOL
xMBPortSerialPutByte( CHAR ucByte )
{
    /* Put a byte in the UARTs transmit buffer. This function is called
     * by the protocol stack if pxMBFrameCBTransmitterEmpty( ) has been
     * called. */
	huart.Instance->TDR = ucByte;
    return TRUE;
}

BOOL
xMBPortSerialGetByte( CHAR * pucByte )
{
    /* Return the byte in the UARTs receive buffer. This function is called
     * by the protocol stack after pxMBFrameCBByteReceived( ) has been called.
     */
	*pucByte = huart.Instance->RDR;
    return TRUE;
}

BOOL UART_IRQ_Handler(USART_TypeDef * usart) {
	if (usart == huart.Instance) {
		if((__HAL_UART_GET_IT(&huart, UART_IT_RXNE) != RESET) && (__HAL_UART_GET_IT_SOURCE(&huart, UART_IT_RXNE) != RESET)) {
			pxMBFrameCBByteReceived();
			__HAL_UART_SEND_REQ(&huart, UART_RXDATA_FLUSH_REQUEST);
			return TRUE;
		}
		if((__HAL_UART_GET_IT(&huart, UART_IT_TXE) != RESET) &&(__HAL_UART_GET_IT_SOURCE(&huart, UART_IT_TXE) != RESET)) {
			pxMBFrameCBTransmitterEmpty();
			return TRUE;
		}
	}
	return FALSE;
}

/**
  ******************************************************************************
  * @file    stm32f3xx_it.c
  * @brief   Interrupt Service Routines.
  ******************************************************************************
  *
  * COPYRIGHT(c) 2016 STMicroelectronics
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  */
/* Includes ------------------------------------------------------------------*/
#include "stm32f3xx_hal.h"
#include "stm32f3xx.h"
#include "stm32f3xx_it.h"

/* USER CODE BEGIN 0 */
#include "port.h"
/* USER CODE END 0 */

/* External variables --------------------------------------------------------*/
extern UART_HandleTypeDef huart1;

/******************************************************************************/
/*            Cortex-M4 Processor Interruption and Exception Handlers         */ 
/******************************************************************************/

/**
* @brief This function handles System tick timer.
*/
void SysTick_Handler(void)
{
  /* USER CODE BEGIN SysTick_IRQn 0 */

  /* USER CODE END SysTick_IRQn 0 */
  HAL_IncTick();
  HAL_SYSTICK_IRQHandler();
  /* USER CODE BEGIN SysTick_IRQn 1 */

  /* USER CODE END SysTick_IRQn 1 */
}

/******************************************************************************/
/* STM32F3xx Peripheral Interrupt Handlers                                    */
/* Add here the Interrupt Handlers for the used peripherals.                  */
/* For the available peripheral interrupt handler names,                      */
/* please refer to the startup file (startup_stm32f3xx.s).                    */
/******************************************************************************/

/**
* @brief This function handles USART1 global interrupt / USART1 wake-up interrupt through EXTI line 25.
*/
void USART1_IRQHandler(void)
{
  /* USER CODE BEGIN USART1_IRQn 0 */
	if (FALSE != UART_IRQ_Handler(USART1))
		return;
  /* USER CODE END USART1_IRQn 0 */
  HAL_UART_IRQHandler(&huart1);
  /* USER CODE BEGIN USART1_IRQn 1 */

  /* USER CODE END USART1_IRQn 1 */
}

/* USER CODE BEGIN 1 */

/* USER CODE END 1 */
/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

eMBErrorCode
eMBRTUSend( UCHAR ucSlaveAddress, const UCHAR * pucFrame, USHORT usLength )
{
    eMBErrorCode    eStatus = MB_ENOERR;
    USHORT          usCRC16;

    ENTER_CRITICAL_SECTION(  );

    /* Check if the receiver is still in idle state. If not we where to
     * slow with processing the received frame and the master sent another
     * frame on the network. We have to abort sending the frame.
     */
    if( eRcvState == STATE_RX_IDLE )
    {
        /* First byte before the Modbus-PDU is the slave address. */
        pucSndBufferCur = ( UCHAR * ) pucFrame - 1;
        usSndBufferCount = 1;

        /* Now copy the Modbus-PDU into the Modbus-Serial-Line-PDU. */
        pucSndBufferCur[MB_SER_PDU_ADDR_OFF] = ucSlaveAddress;
        usSndBufferCount += usLength;

        /* Calculate CRC16 checksum for Modbus-Serial-Line-PDU. */
        usCRC16 = usMBCRC16( ( UCHAR * ) pucSndBufferCur, usSndBufferCount );
        ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 & 0xFF );
        ucRTUBuf[usSndBufferCount++] = ( UCHAR )( usCRC16 >> 8 );


        usSndBufferCount++; // вот тут этот костыль обитает


        /* Activate the transmitter. */
        eSndState = STATE_TX_XMIT;
        vMBPortSerialEnable( FALSE, TRUE );
    }
    else
    {
        eStatus = MB_EIO;
    }
    EXIT_CRITICAL_SECTION(  );
    return eStatus;
}