This snippet code is to test GPIO on Cubieboard A20

Cubieboard_A20_GPIO_test.c

/*  
    This snippet code is to test GPIO on Cubieboard A20.

    The main loop blinks two LEDs waiting a button click (conected in PORT_BTN) via interrupt,
    using funcion poll and wont consuming 100% of cpu.

    This code was tested with:

     * Cubiebord A20 (armv7)
     * Armbian 21.02.3 (Ubuntu based)
     * Kernel 5.10.21-sunxi
     * gcc 9.3.0

    Schematic:

        +---------------+                         LED2
     1  | VCC 5V | PH15 | ---<220_Ohm>------------->|--------+
     2  |        | PH14 | ---<220_Ohm>--------+              |
     3  |        | PB18 |                     |   LED1       |
     .  |    .   |  .   |         BTN         +---->|--------+
     .  |    .   |  .   |       ___|___                      |
     .  |    .   |  .   |    +--o     o----------------------+
    10  |   GND  | GND  |    |                               |
     .  |    .   |  .   |    |                               |
     .  |    .   |  .   |    |                              GND
     .  |    .   |  .   |    |
    21  |        | PE08 | ---+----<2k2_Ohm>----o VCC
    22  |        | PE09 |
    23  |        | PE10 |
    24  |        | PE11 |
        +---------------+

    * Using 2k2 pull up resistor. Cubieboard have internal pull up in someones PINs, but in this moment I dont
      know how configure it.

    Pin reference:   https://linux-sunxi.org/A20/PIO
    Pin reference 2: https://abhinavgupta2812.files.wordpress.com/2013/08/gpio_defination_large.jpg
    Pool function reference:  https://man7.org/linux/man-pages/man2/ppoll.2.html


    Author:  Angelo Araujo
    Date:    2021-03-27

*/

#include <fcntl.h>
#include <stdio.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

/* Main defines. You can change here for your tests */
#define PORT_BTN  238  /* PH14 = 238 */
#define PORT_LED1 239  /* PH15 = 239 */
#define PORT_LED2 136  /* PE08 = 136 */

/* IN OUT used in direction function */
#define IN  1
#define OUT 0

/* NONE BOTH FALLING used in edge funcion */
#define NONE    0
#define BOTH    1
#define FALLING 2
#define RISING  3

/* EXPORT UNERPORT used in export funcion */
#define EXPORT   0
#define UNEXPORT 1

/* Acessory funcion. This converts to string */
#define STR_(X) #X
/* Acessory funcion. This makes sure the argument is expanded before converting to string */
#define STR(X) STR_(X)

/* Wait time test to the things works */
#define WAIT_TIME 1

/* poll wait time */
#define TIME_MS_POLL_WAIT 500

/* Var used to stop loop with ctrl + c (SIGINT) */
static int keepRunning = 1;

/* Acessory funcion. Used to stop main loop. */
void sig_handler(int signo) {
  if (signo == SIGINT) {
     keepRunning = 0;
  }
}

/* Support funcions */

/* Export example: echo 239 > /sys/class/gpio/export */
void gpio_export(int port_num, int export_unexport) {
	int fd, w;
	char s_port[4], s_path[50];
	sprintf(s_path, "/sys/class/gpio/%s", (export_unexport ? "unexport" : "export"));
	sprintf(s_port, "%d", port_num);
	fd = open(s_path, O_WRONLY);
	w = write(fd, s_port, 4);
    printf("EXPORT PIN %s exit: %d\n", s_port, w);
    if (w == -1) {
        printf("errno: %d - %s \n", errno, strerror(errno));
    }
	close(fd);
}

/* Direction example: echo out > /sys/class/gpio/gpio239/direction */
void gpio_set_direction(int port_num, int in_or_out) {
	int fd, w;
    char s_path[50];
    sprintf(s_path, "/sys/class/gpio/gpio%d/direction", port_num);
	fd = open(s_path, O_WRONLY);
	w = write(fd, in_or_out == 1 ? "in" : "out", 6);
    printf("DIRECTION PIN %d exit: %d\n", port_num, w);
	close(fd);
}

/* Edge example: echo both > /sys/class/gpio/gpio239/edge */
void gpio_set_edge(int port_num, int edge) {
	int fd, w;
    char s_path[50];
	sprintf(s_path, "/sys/class/gpio/gpio%d/edge", port_num);
	fd = open(s_path, O_WRONLY);
	w = write(fd, "both", 5);
    printf("EDGE PIN %d exit: %d\n", port_num, w);
	close(fd);
}

/* Set value example: echo 1 > /sys/class/gpio/gpio239/value */
void gpio_set_value(int port_num, int value) {
	int fd;
    char s_path[50], s_value[5];
	sprintf(s_path, "/sys/class/gpio/gpio%d/value", port_num);
	sprintf(s_value, "%d", value);
	fd = open(s_path, O_WRONLY);
	write(fd, s_value, 4);
	close(fd);
}



int main(){

	int i = 0, fd, ret;
	char c;
	struct pollfd pfd;
	
	/* SINGAL HANDLER */
 	if (signal(SIGINT, sig_handler) == SIG_ERR) {
  		printf("\nOps! Can't catch SIGINT.\n");
	}

	/* Enable GPIO */
	gpio_export(PORT_BTN, EXPORT);
	gpio_export(PORT_LED1, EXPORT);
	gpio_export(PORT_LED2, EXPORT);
	
	/* Set direction of GPIO pins */
	gpio_set_direction(PORT_BTN, IN);
	gpio_set_direction(PORT_LED1, OUT);
	gpio_set_direction(PORT_LED2, OUT);
	
	/* Sleep is needed for correct function. If remove wont work. */
	sleep(WAIT_TIME);

	gpio_set_edge(PORT_BTN, BOTH);

	
	/* Wait for event, repeat (i) times */ 
	fd = open("/sys/class/gpio/gpio" STR(PORT_BTN) "/value", O_RDONLY);
	pfd.fd = fd;
	pfd.events = POLLPRI;
	
    /* Main loop, won't consume 100% cpu. */
	while (1) {
		i++;
        
        /* Blink LEDs inverse  */
    	gpio_set_value(PORT_LED1, (i) % 2);
    	gpio_set_value(PORT_LED2, (i+1) % 2);
    
		lseek(fd, 0, SEEK_SET);
        
        /* int poll(struct pollfd *fds, nfds_t nfds, int timeout); */
        ret = poll(&pfd, 1, TIME_MS_POLL_WAIT);
    	read(fd, &c, sizeof(c));
		
		printf("%6d : ", i);
    
		if (ret == 0) {
		
        	printf("Timeout OK\n");
        
        } else {
        
			if(c == '0') {
            
            	printf("-------------------------------------------@@@@@  Push (Readed value of c: %d)\n", c);
                
                /* Set 1. Turn on LEDS on button push for 1 second. */
           		gpio_set_value(PORT_LED1, 1);
				gpio_set_value(PORT_LED2, 1);
            
           		sleep(0.7);
            
            }
			else {
            
				printf("------------------@@@@@  Release (Readed value of c: %d)\n", c);
            
            }
    	}
    
    	if (keepRunning == 0) {
			printf("\n Stoped by Ctrl+C (SIGINT). \n");
			break;
		}
	}

	close(fd);
	
	gpio_export(PORT_BTN, UNEXPORT);
	gpio_export(PORT_LED1, UNEXPORT);
	gpio_export(PORT_LED2, UNEXPORT);

	return(0);
}