Initial commit

src/main.c

@@ -0,0 +1,156 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <syslog.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#define IN	0
+#define OUT	1
+
+#define LOW	0
+#define HIGH	1
+
+#define PIN	24
+#define POUT	4
+
+#define BUF_SIZE	3
+#define DIRECTION_MAX	35
+#define VALUE_MAX	30
+
+static int gpio_export(int pin)
+{
+    char buffer[BUF_SIZE];
+    ssize_t bytes_written;
+    int fd;
+
+    fd = open("/sys/class/gpio/export", O_WRONLY);
+    if(-1 == fd) {
+        fprintf(stderr, "Failed to open export for writing!\n");
+        return -1;
+    }
+
+    bytes_written = snprintf(buffer, BUF_SIZE, "%d", pin);
+    write(fd, buffer, bytes_written);
+    close(fd);
+
+    return 0;
+}
+
+static int gpio_unexport(int pin)
+{
+    char buffer[BUF_SIZE];
+    ssize_t bytes_written;
+    int fd;
+
+    fd = open("/sys/class/gpio/unexport", O_WRONLY);
+    if(-1 == fd) {
+        fprintf(stderr, "Failed to open unexport for writing!\n");
+        return -1;
+    }
+
+    bytes_written = snprintf(buffer, BUF_SIZE, "%d", pin);
+    write(fd, buffer, bytes_written);
+    close(fd);
+
+    return 0;
+}
+
+static int gpio_direction(int pin, int dir)
+{
+    static const char directions_str[]  = "in\0out";
+    char path[DIRECTION_MAX];
+    int fd;
+
+    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/direction", pin);
+    fd = open(path, O_WRONLY);
+    if(-1 == fd) {
+        fprintf(stderr, "Failed to open gpio direction for writing!\n");
+        return -1;
+    }
+
+    if(-1 == write(fd, &directions_str[IN == dir ? 0 : 3], IN == dir ? 2 : 3)) {
+        fprintf(stderr, "Failed to set direction!\n");
+        return -1;
+    }
+    close(fd);
+
+    return 0;
+}
+
+static int gpio_read(int pin)
+{
+    char path[VALUE_MAX];
+    char value_str[BUF_SIZE];
+    int fd;
+
+    snprintf(path, VALUE_MAX, "/sys/class/gpio/gpio%d/value", pin);
+    fd = open(path, O_RDONLY);
+    if(-1 == fd) {
+        fprintf(stderr, "Failed to open gpio value for reading!\n");
+        return -1;
+    }
+
+    if(-1 == read(fd, value_str, BUF_SIZE)) {
+        fprintf(stderr, "Failed to read value!\n");
+        return -1;
+    }
+    close(fd);
+
+    return(atoi(value_str));
+}
+
+static int gpio_write(int pin, int value)
+{
+    static const char s_values_str[] = "01";
+    char path[VALUE_MAX];
+    int fd;
+
+    snprintf(path, VALUE_MAX, "/sys/class/gpio/gpio%d/value", pin);
+    fd = open(path, O_WRONLY);
+    if(-1 == fd) {
+        fprintf(stderr, "Failed to open gpio value for writing!\n");
+        return -1;
+    }
+
+    if(1 != write(fd, &s_values_str[LOW == value ? 0 : 1], 1)) {
+        fprintf(stderr, "Failed to write value!\n");
+        return -1;
+    }
+    close(fd);
+
+    return 0;
+}
+
+int main(void)
+{
+    int repeat = 10;
+
+    if(-1 == gpio_export(POUT) || -1 == gpio_export(PIN)) {
+        return(1);
+    }
+
+    if(-1 == gpio_direction(POUT, OUT) || -1 == gpio_direction(PIN, IN)) {
+        return(2);
+    }
+
+    do {
+        if(-1 == gpio_write(POUT, repeat % 2)) {
+            return(3);
+        }
+
+	printf("I'm reading %d in GPIO %d\n", gpio_read(PIN), PIN);
+        usleep(500 * 1000);
+    } while(repeat--);
+
+    if(-1 == gpio_unexport(POUT) || -1 == gpio_unexport(PIN)) {
+	return(4);
+    }
+
+    return(0);
+}
+