Add the GPIO handling code for the RaspberryPi. Still need to integrate RaspberryPi into the Makefile.

gpio_sysfs.c

@@ -0,0 +1,197 @@
+/*
+ * gpio_sysfs.c
+ *
+ * Raspberry Pi GPIO handling using sysfs interface.
+ * Guillermo A. Amaral B. <g@maral.me>
+ *
+ */
+
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "gpio_sysfs.h"
+
+#define IN  0
+#define OUT 1
+
+#define LOW  0
+#define HIGH 1
+
+#define PIN  24 /* P1-18 */
+#define POUT 4  /* P1-07 */
+
+
+/**
+ * Export GPIO pin for use. 
+ * @param pin - The pin number to be used.
+ * @returns Zero on success -1 on failure.  
+ */
+int gpio_export(int pin)
+{
+#define BUFFER_MAX 3
+	char buffer[BUFFER_MAX];
+	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, BUFFER_MAX, "%d", pin);
+	write(fd, buffer, bytes_written);
+	close(fd);
+	return(0);
+}
+
+/**
+ * Unexport GPIO pin for use. 
+ * @param pin - The pin number to be used.
+ * @returns Zero on success -1 on failure.
+ */
+int gpio_unexport(int pin)
+{
+	char buffer[BUFFER_MAX];
+	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, BUFFER_MAX, "%d", pin);
+	write(fd, buffer, bytes_written);
+	close(fd);
+	return(0);
+}
+
+/**
+ * Set GPIO pin direction. 
+ * @param pin - The pin number to be used.
+ * @param dir - The desired pin directio, 1 = out, 0 = in.
+ * @returns Zero on success -1 on failure.
+ */
+int gpio_direction(int pin, int dir)
+{
+	static const char s_directions_str[]  = "in\0out";
+
+#define DIRECTION_MAX 35
+	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, &s_directions_str[IN == dir ? 0 : 3], IN == dir ? 2 : 3)) {
+		fprintf(stderr, "Failed to set direction!\n");
+		return(-1);
+	}
+
+	close(fd);
+	return(0);
+}
+
+/**
+ * Read GPIO pin state. 
+ * @param pin - The pin number to be read.
+ * @returns The pin state 0 or 1.
+ */
+int gpio_read(int pin)
+{
+#define VALUE_MAX 30
+	char path[VALUE_MAX];
+	char value_str[3];
+	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, 3)) {
+		fprintf(stderr, "Failed to read value!\n");
+		return(-1);
+	}
+
+	close(fd);
+
+	return(atoi(value_str));
+}
+
+/**
+ * Write GPIO pin state.
+ * @param pin - The pin number to be written to.
+ * @returns The desired pin state 0 or 1.
+ */
+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);
+}
+
+#ifdef TEST_GPIO_SYSFS
+
+/* This test blinks GPIO 4 (P1-07) while reading GPIO 24 (P1_18) */
+int main(int argc, char *argv[])
+{
+	int repeat = 10;
+
+	// Enable GPIO pins
+	if (-1 == gpio_export(POUT) || -1 == gpio_export(PIN))
+		return(1);
+
+	// Set GPIO directions
+	if (-1 == gpio_direction(POUT, OUT) || -1 == gpio_direction(PIN, IN))
+		return(2);
+
+	do {
+		// Write GPIO value
+		if (-1 == gpio_write(POUT, repeat % 2))
+			return(3);
+
+		// Read GPIO value
+		printf("I'm reading %d in GPIO %d\n", gpio_read(PIN), PIN);
+
+		usleep(500 * 1000);
+	}
+	while (repeat--);
+
+	// Disable GPIO pins
+	if (-1 == gpio_unexport(POUT) || -1 == gpio_unexport(PIN))
+		return(4);
+
+	return(0);
+}
+
+#endif // TEST_GPIO_SYSFS
+

gpio_sysfs.h

@@ -0,0 +1,21 @@
+#ifndef GPIO_SYSFS_H
+#define GPIO_SYSFS_H
+
+#define IN  0
+#define OUT 1
+
+#define LOW  0
+#define HIGH 1
+
+int gpio_export (int pin);
+
+int gpio_unexport (int pin);
+
+int gpio_direction (int pin, int dir);
+
+int gpio_read (int pin);
+
+int gpio_write (int pin, int value);
+
+#endif // GPIO_SYSFS_H
+