Question for Library 31- USB HID Host for STM32F4 by ftm

/* Include core modules */
#include "stm32f4xx.h"
/* Include my libraries here */
#include "defines.h"
#include "tm_stm32f4_disco.h"
#include "tm_stm32f4_delay.h"
#include "tm_stm32f4_usb_hid_host.h"
#include <stm32f4xx_usart.h>

#include <stdio.h>

void init_usart2(void);
int diff(int16_t *prevBuff, int16_t *nowBuff);

int main(void) {
	TM_USB_HIDHOST_Result_t USB_HID_Status;		/* USB HID Host status */
	TM_USB_HIDHOST_Keyboard_t Keyboard_Data;	/* Keyboard handler */
	TM_USB_HIDHOST_Mouse_t Mouse_Data;			/* Mouse handler */

	int16_t nowBuff[5];
	int16_t prevBuff[5];
	const int mouseDataSize = 5;

	/* Initialize system */
	SystemInit();

	/* Leds init */
	TM_DISCO_LedInit();

	/* Delay init */
	TM_DELAY_Init();

	/* Init USB HID */
	TM_USB_HIDHOST_Init();

	init_usart2();

	while (1) {
		/* Process USB HID */
		/* This must be called periodically */

		int change_index = 0, transfer_index = 0;

		TM_USB_HIDHOST_Process();

		/* Get connected device */
		USB_HID_Status = TM_USB_HIDHOST_Device();

		/* Switch status */
		switch (USB_HID_Status) {
			/* Keyboard connected */
			case TM_USB_HIDHOST_Result_KeyboardConnected:

				/* GREEN led ON */
				TM_DISCO_LedOn(LED_GREEN);

				/* Get keyboard data */
				TM_USB_HIDHOST_ReadKeyboard(&Keyboard_Data);
				/* Check if keyboard button is pressed */
				if (Keyboard_Data.ButtonStatus == TM_USB_HIDHOST_Button_Pressed) {
					if (Keyboard_Data.Button == 'b') {			/* Turn on RED led on 'b' button */
						TM_DISCO_LedOn(LED_RED);
					} else if (Keyboard_Data.Button == 'v') {	/* Turn off RED led on 'v' button */
						TM_DISCO_LedOff(LED_RED);
					}
				}

				break;

			/* Mouse connected */
			case TM_USB_HIDHOST_Result_MouseConnected:

				/* RED led ON */
				TM_DISCO_LedOn(LED_RED);

				/* Get mouse data */
				TM_USB_HIDHOST_ReadMouse(&Mouse_Data);

				nowBuff[0] = Mouse_Data.LeftButton;
				nowBuff[1] = Mouse_Data.RightButton;
				nowBuff[2] = Mouse_Data.MiddleButton;
				nowBuff[3] = Mouse_Data.DiffX;
				nowBuff[4] = Mouse_Data.DiffY;


				//check this mouse signals is different from previous
				if( !diff(prevBuff,nowBuff) )
				{
					//Recode now mouse signals.
					for (change_index = 0; change_index<mouseDataSize; change_index++)
					{
						prevBuff[change_index] = nowBuff[change_index];
					}

					//transfer mouse data to usart
					for ( transfer_index=0; transfer_index <mouseDataSize; transfer_index++)
					{
						USART_SendData(USART2, nowBuff[transfer_index]);
						while (USART_GetFlagStatus(USART2, USART_FLAG_TC) == RESET);
					}
				}

				break;

			/* No device connected */
			case TM_USB_HIDHOST_Result_Disconnected:

				/* Turn off leds */
				TM_DISCO_LedOff(LED_RED | LED_GREEN);

				break;

			/* Device is not supported */
			case TM_USB_HIDHOST_Result_DeviceNotSupported:

				/* Device is not supported */
				/* Toggle leds forever */
				TM_DISCO_LedToggle(LED_RED | LED_GREEN);
				/* Delay */
				Delayms(50);

				break;

			/* Error occurred somewhere */
			case TM_USB_HIDHOST_Result_Error:

				/* Error occurred */
				/* Toggle RED LED forever */
				TM_DISCO_LedToggle(LED_RED);
				/* Delay */
				Delayms(50);

				break;

			/* Library is not initialized */
			case TM_USB_HIDHOST_Result_LibraryNotInitialized:

				/* Library is not initialized */
				/* Toggle GREEN LED */
				TM_DISCO_LedToggle(LED_GREEN);
				/* Delay */
				Delayms(50);

				break;
		}
	}
}

void init_usart2(void){

	GPIO_InitTypeDef GPIO_InitStructure;
	USART_InitTypeDef USART_InitStructure;

	/* enable peripheral clock for USART2 */
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);


	/* GPIOA clock enable */
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

	/* GPIOA Configuration:  USART2 TX on PA2 */
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;
	GPIO_Init(GPIOA, &GPIO_InitStructure);

	/* Connect USART2 pins to AF2 */
	// TX = PA2
	GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_USART2);

	USART_InitStructure.USART_BaudRate = 9600;
	USART_InitStructure.USART_WordLength = USART_WordLength_8b;
	USART_InitStructure.USART_StopBits = USART_StopBits_1;
	USART_InitStructure.USART_Parity = USART_Parity_No;
	USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
	USART_InitStructure.USART_Mode = USART_Mode_Tx;
	USART_Init(USART2, &USART_InitStructure);

	USART_Cmd(USART2, ENABLE); // enable USART2

}

int diff(int16_t *prevBuff, int16_t *nowBuff)
{
	int buffSize = 5, index;

	for ( index = 0 ; index < buffSize ; index++)
	{
		if (prevBuff[index] != nowBuff[index])
			return 0;
	}
	return 1;
}