I am building a device to measure the frequency of the BLDC motor. I am using stm32 Bluepill for this.

I am using an LCD to display the frequency using the timer in the blue pill. The frequency is displayed when I give the input frequency, but when I remove the input frequency, it does not display 0. How to display the freq to 0 if the input is not given. Here is the code for the above device.

/* USER CODE BEGIN Header */
/**
******************************************************************************
* @file : main.c
* @brief : Main program body
******************************************************************************
* @attention
*
* Copyright (c) 2022 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
*/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "stdio.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */

/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
I2C_HandleTypeDef hi2c2;

TIM_HandleTypeDef htim2;

/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2C2_Init(void);
static void MX_TIM2_Init(void);
void init();
void lcd_command(unsigned char);
void lcd_data(unsigned char);
void lcd_display(unsigned char *s);
unsigned char array[]={"HELLO"};
unsigned int overflow=0;
char upper,lower;
int c,status;
char high,low;
int rise=0;
int down=0;
uint32_t value1;
uint32_t value2;
uint32_t difference;
int first_captured=0;
int frequency=0;
float refclock;

#define TIMCLOCK 72000000
#define PRESCALAR 72
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
* @brief The application entry point.
* @retval int
*/
void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim)
{

if(htim->Channel==HAL_TIM_ACTIVE_CHANNEL_1)
{
if(first_captured==0)
{
rise++;
value1=HAL_TIM_ReadCapturedValue(htim,TIM_CHANNEL_1);
value2=value1;
first_captured=1;

}
else
{
value2=HAL_TIM_ReadCapturedValue(htim,TIM_CHANNEL_1);
down++;
if(value2>value1)
difference=value2-value1;
if(value1>value2)
difference=(65536-value1)+value2;
refclock =TIMCLOCK/PRESCALAR;
frequency=refclock/difference;
__HAL_TIM_SET_COUNTER(htim,0);
first_captured=0;



}
}
}

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef* htim)
{
overflow++;
}
int main(void)
{
/* USER CODE BEGIN 1 */

/* USER CODE END 1 */

/* MCU Configuration--------------------------------------------------------*/

/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();

/* USER CODE BEGIN Init */

/* USER CODE END Init */

/* Configure the system clock */
SystemClock_Config();

/* USER CODE BEGIN SysInit */

/* USER CODE END SysInit */

/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_I2C2_Init();
MX_TIM2_Init();
/* USER CODE BEGIN 2 */

/* USER CODE END 2 */

/* Infinite loop */
/* USER CODE BEGIN WHILE */

HAL_TIM_IC_Start_IT(&htim2,TIM_CHANNEL_1);
init();

while (1)
{
if(value2==value1)
{
frequency=0;
}
status=HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_0);
lcd_command(0x80);
HAL_Delay(30);
lcd_display("FREQ:");
//HAL_Delay(20);


lcd_command(0x86);
c=((frequency/100)%10);

if(c!=0)
{
lcd_data (((frequency/100)%10)+48);
lcd_data (((frequency/10)%10)+48);
lcd_data (((frequency/1)%10)+48);
}



if(c==0)
{
lcd_data (((frequency/10)%10)+48);
lcd_data (((frequency/1)%10)+48);
lcd_data(0x20);
}


//lcd_display(frequency);
lcd_command(0x8A);
lcd_display("Hz");


if(frequency>99)
{
HAL_GPIO_WritePin(GPIOB,GPIO_PIN_4,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOB,GPIO_PIN_8,GPIO_PIN_RESET);
}
else
{
HAL_GPIO_WritePin(GPIOB,GPIO_PIN_8,GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOB,GPIO_PIN_4,GPIO_PIN_RESET);
}
/* USER CODE END WHILE */

/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}

void init()
{
/*HAL_Delay(500);
lcd_command(0x02);
HAL_Delay(100);
lcd_command(0x28);
HAL_Delay(50);
lcd_command(0x0E);
HAL_Delay(100);
lcd_command(0x0F);
HAL_Delay(100);
lcd_command(0x06);
HAL_Delay(100);
lcd_command(0x80);
HAL_Delay(100);*/

// 4 bit initialisation
HAL_Delay(50); // wait for >40ms
lcd_command (0x30);
HAL_Delay(5); // wait for >4.1ms
lcd_command (0x30);
HAL_Delay(1); // wait for >100us
lcd_command (0x30);
HAL_Delay(10);
lcd_command (0x20); // 4bit mode
HAL_Delay(10);

// dislay initialisation
lcd_command (0x28); // Function set --> DL=0 (4 bit mode), N = 1 (2 line display) F = 0 (5x8 characters)
HAL_Delay(1);
lcd_command (0x08); //Display on/off control --> D=0,C=0, B=0 ---> display off
HAL_Delay(1);
lcd_command (0x01); // clear display
HAL_Delay(1);
HAL_Delay(1);
lcd_command (0x06); //Entry mode set --> I/D = 1 (increment cursor) & S = 0 (no shift)
HAL_Delay(1);
lcd_command (0x0C); //Display on/off control --> D = 1, C and B = 0. (Cursor and blink, last two bits)

}

void lcd_command(unsigned char i)
{

uint8_t data[4];
lower=(i<<4)&0xF0;
upper=i&0xF0;
data[0]=upper|0x0C;
data[1]=upper|0x08;
data[2]=lower|0x0C;
data[3]=lower|0x08;
HAL_I2C_Master_Transmit(&hi2c2,0x4E,(uint8_t*)data ,4,100);
}

void lcd_data(unsigned char i)
{

uint8_t data[4];
low=(i<<4)&0xF0;
high=i&0xF0;
data[0]=high|0x0D;
data[1]=high|0x09;
data[2]=low|0x0D;
data[3]=low|0x09;
HAL_I2C_Master_Transmit(&hi2c2,0x4E,(uint8_t*)data, 4, 100);
}

void lcd_display(unsigned char *s)
{
while(*s)
{
lcd_data(*s++);
}
//HAL_Delay(50);



}

/**
* @brief System Clock Configuration
* @retval None
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}

/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
{
Error_Handler();
}
}

/**
* @brief I2C2 Initialization Function
* @param None
* @retval None
*/
static void MX_I2C2_Init(void)
{

/* USER CODE BEGIN I2C2_Init 0 */

/* USER CODE END I2C2_Init 0 */

/* USER CODE BEGIN I2C2_Init 1 */

/* USER CODE END I2C2_Init 1 */
hi2c2.Instance = I2C2;
hi2c2.Init.ClockSpeed = 100000;
hi2c2.Init.DutyCycle = I2C_DUTYCYCLE_2;
hi2c2.Init.OwnAddress1 = 0;
hi2c2.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
hi2c2.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
hi2c2.Init.OwnAddress2 = 0;
hi2c2.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
hi2c2.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
if (HAL_I2C_Init(&hi2c2) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN I2C2_Init 2 */

/* USER CODE END I2C2_Init 2 */

}

/**
* @brief TIM2 Initialization Function
* @param None
* @retval None
*/
static void MX_TIM2_Init(void)
{

/* USER CODE BEGIN TIM2_Init 0 */

/* USER CODE END TIM2_Init 0 */

TIM_ClockConfigTypeDef sClockSourceConfig = {0};
TIM_MasterConfigTypeDef sMasterConfig = {0};
TIM_IC_InitTypeDef sConfigIC = {0};

/* USER CODE BEGIN TIM2_Init 1 */

/* USER CODE END TIM2_Init 1 */
htim2.Instance = TIM2;
htim2.Init.Prescaler = 72-1;
htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
htim2.Init.Period = 65535;
htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
{
Error_Handler();
}
sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
{
Error_Handler();
}
if (HAL_TIM_IC_Init(&htim2) != HAL_OK)
{
Error_Handler();
}
sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
{
Error_Handler();
}
sConfigIC.ICPolarity = TIM_INPUTCHANNELPOLARITY_RISING;
sConfigIC.ICSelection = TIM_ICSELECTION_DIRECTTI;
sConfigIC.ICPrescaler = TIM_ICPSC_DIV1;
sConfigIC.ICFilter = 15;
if (HAL_TIM_IC_ConfigChannel(&htim2, &sConfigIC, TIM_CHANNEL_1) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN TIM2_Init 2 */

/* USER CODE END TIM2_Init 2 */

}

/**
* @brief GPIO Initialization Function
* @param None
* @retval None
*/
static void MX_GPIO_Init(void)
{

/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOD_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
__HAL_RCC_GPIOB_CLK_ENABLE();

}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
* @brief This function is executed in case of error occurrence.
* @retval None
*/
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
__disable_irq();
while (1)
{
}
/* USER CODE END Error_Handler_Debug */
}

#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t *file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */