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--- user:jcavalu3:portfolio:datacomm1 [2013/10/30 15:39] – created jcavalu3
+++ user:jcavalu3:portfolio:datacomm1 [2013/10/31 01:12] (current) – [Tutorial #2: The C Code] jcavalu3
@@ Line 1: / Line 1: @@
+=====Pertinent Links Project: GPIO Tutorials #1 and #2=====
+====Project #1: The Command Line====
+In this project, I was given a few links to websites that I needed to visit to begin accessing the GPIO pins on the Raspberry Pi. The [[https://sites.google.com/site/semilleroadt/raspberry-pi-tutorials/gpio|first website]] was used to access the GPIO pins on the command line:
+First, in order to access any GPIO pins, the user must use SuperUser or just sudo before any command accessing the pins.
+According to the website, when writing to the ./export file in the /sys/class/gpio/ subdirectory, a file is created with a GPIO structure that is set up according to the input from the user. For this example, the user was told to create this file for GPIO11 so the user can access that pin and handle the LED.
+To create the GPIO file, the user must input the following:
+<cli>
+echo 11 > /sys/class/gpio/export
+</cli>
+Next, the Pin Direction must be set as Input or Output:
+<cli>
+echo out > /sys/class/gpio/gpio11/direction
+</cli>
+Lastly, a value of '1' must be given to turn on the LED:
+<cli>
+echo 1 > /sys/class/gpio/gpio11/value
+</cli>
+This should have done it!
+To turn it off, just repeat the step that turned the LED on, replacing the '1' with a '0'.
+<cli>
+echo 0 > /sys/class/gpio/gpio11/value
+</cli>
+To delete the file access, repeat the step that first created the file (export), but instead accessing the 'unexport' file.
+<cli>
+echo 11 > /sys/class/gpio/unexport
+</cli>
+====Project #2: The C Code====
+This tutorial used C code to access the GPIO pins, which is what most of (if not the rest) of this class will focus on, the C code method of accessing the pins.
+From the [[https://sites.google.com/site/semilleroadt/raspberry-pi-tutorials/gpio|second website]] I found the code to access the pins through the C language.
+The necessary code is as follows:
+rpi.h
+<code c>
+#include <stdio.h>
+
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <fcntl.h>
+
+#include <unistd.h>
+
+#define BCM2708_PERI_BASE   0x20000000
+#define GPIO_BASE       (BCM2708_PERI_BASE + 0X200000) // GPIO controller
+
+#define BLOCK_SIZE      (4*1024)
+
+//IO Access
+struct bcm2835_peripheral {
+     unsigned long addr_p;
+     int mem_fd;
+     void *map;
+     volatile unsigned int *addr;
+
+};
+
+// struct bcm2835_peripheral gpio = {GPIO_BASE};
+
+extern struct bcm2835_peripheral gpio; // They have to be found somewhere, b    ut can't be in the header
+
+
+// GPIO setup macros. Always use INP_GPIO(X) before using OUT_GPIO(x)
+#define INP_GPIO(g)         *(gpio.addr + ((g)/10)) &= ~(7<<(((g)%10)*3))
+#define OUT_GPIO(g)         *(gpio.addr + ((g)/10)) |=  (1<<(((g)%10)*3))
+#define SET_GPI_ALT(G,a)    *(gpio.addr + (((g)/10))) |= (((a)<=3?(a) + 4:(a    )==4?3:2)<<(((g)%10)*3))
+
+#define GPIO_SET            *(gpio.addr + 7)    // sets   bits which are 1 i    gnores bits which are 0
+#define GPIO_CLR            *(gpio.addr + 10)   // chears bits which are 1 i    gnores bits which are 0
+
+#define GPIO_READ(g)        *(gpio.addr + 13) &= (1<<(g))
+</code>
+rpi.c
+<code c>
+#include "rpi.h"
+
+struct bcm2835_peripheral gpio = {GPIO_BASE};
+
+// Exposes the physical address defined in the passed structure using mmap o    n /dev/mem
+int map_peripheral(struct bcm2835_peripheral *p)
+{
+     // Open /dev/mem
+     if ((p->mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
+         printf("Failed to open /dev/mem, try checking permissions.\n");
+         return -1;
+     }
+
+     p->map = mmap(
+         NULL,
+         BLOCK_SIZE,
+         PROT_READ|PROT_WRITE,
+         MAP_SHARED,
+         p->mem_fd,      // File descriptor to physical memory virtual file '    /dev/mem'
+         p->addr_p       // Address in physical map that we want this memory     block to expose
+         );
+
+     if (p->map == MAP_FAILED) {
+         perror("mmap");
+         return -1;
+     }
+
+     p->addr = (volatile unsigned int *)p->map;
+
+     return 0;
+}
+
+void unmap_peripheral(struct bcm2835_peripheral *p) {
+
+     munmap(p->map, BLOCK_SIZE);
+     close(p->mem_fd);
+}
+</code>
+The code that is seen above is what is necessary for the program that turns on the LED to work.
+main.c
+<code c>
+#include "rpi.h"
+
+int main()
+{
+     if(map_peripheral(&gpio) == -1)
+     {
+         printf("Failed to map the physical GPIO registers into the virtual m    emory space.\n");
+         return -1;
+     }
+
+     // Define pin 7 as output
+     INP_GPIO(7); // Sets GPIO pin as input
+     OUT_GPIO(7); // Sets GPIO pin as output
+
+     while(1)
+     {
+         // Toggle pin 7 (blink a LED!)
+         GPIO_SET = 1 << 7; // Sets the GPIO pin on
+         usleep(1000000); // sleep for one second
+
+         GPIO_CLR = 1 << 7; // Clears the GPIO pin/turns it off
+         usleep(1000000); // sleep for one second
+     }
+     return 0;
+}
+</code>
+The program has been run and successfully turns the LED on and off.

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