Experiment 2 LED button PWM 2021/11/15

Run this command to stop led flashing
/etc/rc.d/init.d/leds stop

led

#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<time.h>
int main() {
    
	int fd,i;
	fd=open("/dev/leds",O_WRONLY);
	if(fd<0) {
    
		printf("Open leds error!\n");
		exit(1);
	}
	for(i=0;i<4;i++) ioctl(fd,0,i);
	for(;;) {
    
		for(i=0;i<4;i++)
		ioctl(fd,0,i);
		for(i=0;i<4;i++) {
    
			ioctl(fd,1,i);
			sleep(1);
		}
	}
	close(fd);
	return 0;
}

button

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<fcntl.h>
int main() {
    
	int fd,i;
	char key[4]={
    '0'};
	fd=open("/dev/buttons",O_RDONLY);
	if(fd<0) {
    
		printf("Open buttons error!\n");
		exit(1);
	}
	for(;;) {
    
		read(fd,key,sizeof(key));
		for(i=0;i<4;i++) {
    
			usleep(50000);
			for(i=0;i<4;i++) 
				if(key[i]=='1') printf("key%d\n",i+1);
		}
	}
	close(fd);
	return 0;
}

pwm

#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<time.h>
int main() {
    
	int fd,frq=2000;
	fd=open("/dev/pwm",O_RDONLY);
	if(fd<0) {
    
		printf("Open pwm error!\n");
		exit(1);
	}
	ioctl(fd,1,frq);
	sleep(3);
	ioctl(fd,0);
	close(fd);
	return 0;
}

Ctrl + C  The end of the process 
Ctrl + Z  Pause the process 

improvement

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
int main(void) {
    
	int fd;
	char key[4]={
    '0'};

	fd = open("/dev/buttons",O_RDONLY);
	if (fd<0) {
    
		printf("ERROR\n");
		exit(1);
	}	
	for (;;) {
    
		char now[4];
		int cnt=0;
		int i;
		read(fd,now,sizeof now);
		for (i=0,cnt=0;i<4;i++) {
    
			if (key[i]!=now[i]) {
    
				key[i] = now[i];
				printf("key%d is ",i+1);				
				if(key[i]=='1') printf("down");
				else printf("up");
				cnt++;
			}
		}
		if (cnt) printf("\n");
	}
	close(fd);
	return 0;
}

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