Re-add LED files

It turns out that some users were still using the LED functionality.
Adding it back.

diode_controller/Makefile

@@ -0,0 +1,2 @@
+led:	led.c
+	gcc -ggdb -o led led.c

diode_controller/led.c

@@ -0,0 +1,81 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+/* GPIO registers address */
+#define BCM2708_PERI_BASE  0x20000000
+#define GPIO_BASE          (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
+#define BLOCK_SIZE         (256)
+
+/* GPIO setup macros. Always use GPIO_IN(x) before using GPIO_OUT(x) or GPIO_ALT(x,y) */
+#define GPIO_IN(g)    *(gpio+((g)/10))   &= ~(7<<(((g)%10)*3))
+#define GPIO_OUT(g)   *(gpio+((g)/10))   |=  (1<<(((g)%10)*3))
+#define GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))
+
+#define GPIO_SET(g)   *(gpio+7)  = 1<<(g)  /* sets   bit which are 1, ignores bit which are 0 */
+#define GPIO_CLR(g)   *(gpio+10) = 1<<(g)  /* clears bit which are 1, ignores bit which are 0 */
+#define GPIO_LEV(g)  (*(gpio+13) >> (g)) & 0x00000001
+
+
+
+#define GPIO_4    4
+
+int                mem_fd;
+void              *gpio_map;
+volatile uint32_t *gpio;
+
+int main(int argc, char* argv[])
+{
+     int ret;
+     int i;
+     /* open /dev/mem */
+     mem_fd = open("/dev/mem", O_RDWR|O_SYNC);
+     if (mem_fd == -1) {
+              perror("Cannot open /dev/mem");
+              exit(1);
+     }
+
+     /* mmap GPIO */
+     gpio_map = mmap(NULL, BLOCK_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, mem_fd, GPIO_BASE);
+     if (gpio_map == MAP_FAILED) {
+             perror("mmap() failed");
+             exit(1);
+     }
+      /* Always use volatile pointer! */
+        gpio = (volatile uint32_t *)gpio_map;
+
+
+     GPIO_IN(GPIO_4); /* must use GPIO_IN before we can use GPIO_OUT */
+     GPIO_OUT(GPIO_4);
+
+    //Turn on led
+    while (1) {
+        //printf("Enable LED\n");
+        GPIO_SET(GPIO_4);
+        usleep(1000000);
+        //printf("Disable GPIO\n"); // Does not seem to work?
+        //GPIO_CLR(GPIO_4);
+        //usleep(1000000);
+    }
+    /* Free up ressources */
+        /* munmap GPIO */
+        ret = munmap(gpio_map, BLOCK_SIZE);
+        if (ret == -1) {
+                perror("munmap() failed");
+                exit(1);
+        }
+        /* close /dev/mem */
+        ret = close(mem_fd);
+        if (ret == -1) {
+                perror("Cannot close /dev/mem");
+                exit(1);
+        }
+
+     return EXIT_SUCCESS;
+}