FPGA key experiment

#include <stdio.h>
#include "platform.h"
#include "xparameters.h"
#include "xscugic.h"
#include "xil_exception.h"
#include "xgpio.h"
#include <unistd.h> // usleep() Delay function header file 
#include <stdbool.h>  // bool

#define LED_DEVICE_ID          XPAR_AXI_GPIO_1_DEVICE_ID
#define KEY_DEVICE_ID          XPAR_AXI_GPIO_0_DEVICE_ID

XGpio LEDInst;
XGpio KEYInst;

u8 key_value_pre=0;
u8 key_value_now=0;

int main()
{
    init_platform();

    int status;

// initialization 
    status = XGpio_Initialize(&KEYInst, KEY_DEVICE_ID); // initial KEY
   /*int XGpio_Initialize(XGpio * InstancePtr, u16 DeviceId)
    * function ： initialization XGpio example .
    * Parameters 1： Pointer to the device instance .
    * Parameters 2： equipment ID.
    * return ： Successfully returns XST_SUCCESS, Failure to return XST_DEVICE_NOT_FOUND */
    if(status != XST_SUCCESS)
    // After calling the above function, judge whether the initialization is successful according to the return value , If status It's not equal to XST_SUCCESS Failure 
    	return XST_FAILURE;


    status = XGpio_Initialize(&LEDInst, LED_DEVICE_ID);  // initial LED
    if(status != XST_SUCCESS)
    	return XST_FAILURE;

// The configuration phase 
    XGpio_SetDataDirection(&KEYInst, 1, 1); // set KEY IO direction as in
    /*void XGpio_SetDataDirection(XGpio * InstancePtr, unsigned Channel,u32 DirectionMask)
     * function ： Set the input / output direction of each channel .
     * Parameters 1： Pointer to the device instance .
     * Parameters 2： Ready for operation GPIO The passage of （Vivado Set in gpio IP Setting channel of , by 1 or 2）.
     * Parameters 3： Mask that determines the direction of input and output ,1 An input 0 For export .
     */

    XGpio_SetDataDirection(&LEDInst, 1, 0); // set LED IO direction as out, Set the lamp to output 



    XGpio_DiscreteWrite(&LEDInst, 1, 0x0);// at initial, all LED turn off
    /*void XGpio_DiscreteWrite(XGpio * InstancePtr, unsigned Channel, u32 Data)
     * function ： Write input data to the input device instance .
     * Parameters 1： Examples of equipment 
     * Parameters 2： passageway 
     * Parameters 3： The data to be written 
     * return ： void*/

    printf(">>> Press PL KEY1 ~ KEY4 one by one, and check the PL LED1 ~ LED4\n");
// Actual program execution stage 
    while(1)
    {
        usleep(100000); // 0.1s sleep, to debounce, in common, the meta-state will sustain no more than 20ms
     /*usleep The command is used to delay time in microseconds 
      *1 second =1000 millisecond =1000,000 Microsecond =1000,000,000 nanosecond .
      * Commonly used way 
      * Format ：usleep <us>
      * Delay <us> Microsecond .*/

        key_value_pre=key_value_now;
        key_value_now= XGpio_DiscreteRead(&KEYInst, 1) & 0x0F;
        /* u32 XGpio_DiscreteRead(XGpio * InstancePtr, unsigned Channel)
          * function ： Read current IO state .
          * Parameters 1： Device instance pointer .
          * Parameters 2： passageway .
          * return ：IO Current value .*/
        XGpio_DiscreteWrite(&LEDInst, 1, key_value_now);
        if(key_value_pre!=key_value_now)
        	printf("key state_changed!\n");
    }

    cleanup_platform();
    return 0;
}