//
//  How to access GPIO registers from C-code on the Raspberry-Pi
//  Example program
//  15-January-2012
//  Dom and Gert
//  Revised: 15-Feb-2013


// Access from ARM Running Linux

#define BCM2708_PERI_BASE        0x20000000
#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */


#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)

#define SER_DAT_PIN   26
#define SER_CLK_PIN   19
#define GATE_PIN      13
#define PAR_CLK_PIN    6
#define SENSE_PIN      5

int  mem_fd;
void *gpio_map;

// I/O access
volatile unsigned *gpio;


// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))

#define GPIO_SET *(gpio+7)  // sets   bits which are 1 ignores bits which are 0
#define GPIO_CLR *(gpio+10) // clears bits which are 1 ignores bits which are 0
#define GPIO_ALTER(a) *(gpio+(a==0?10:7))  // alters (a==0: clear, else: set)  bits which are 1 ignores bits which are 0

#define GET_GPIO(g) (*(gpio+13)&(1<<g)) // 0 if LOW, (1<<g) if HIGH

#define GPIO_PULL *(gpio+37) // Pull up/pull down
#define GPIO_PULLCLK0 *(gpio+38) // Pull up/pull down clock

void setup_io();
void drop_privileges();
void put_on_display(char *content);

void printButton(int g)
{
  if (GET_GPIO(g)) // !=0 <-> bit is 1 <- port is HIGH=3.3V
    printf("Button pressed!\n");
  else // port is LOW=0V
    printf("Button released!\n");
}

int main(int argc, char **argv)
{
  int rep;

  // Set up gpi pointer for direct register access
//  setup_io();

  // Drop root privileges
  drop_privileges();

 /************************************************************************\
  * You are about to change the GPIO settings of your computer.          *
  * Mess this up and it will stop working!                               *
  * It might be a good idea to 'sync' before running this program        *
  * so at least you still have your code changes written to the SD-card! *
 \************************************************************************/

  // must use INP_GPIO before we can use OUT_GPIO
  INP_GPIO(SER_DAT_PIN);
  OUT_GPIO(SER_DAT_PIN);
  INP_GPIO(SER_CLK_PIN);
  OUT_GPIO(SER_CLK_PIN);
  INP_GPIO(GATE_PIN);
  OUT_GPIO(GATE_PIN);
  INP_GPIO(PAR_CLK_PIN);
  OUT_GPIO(PAR_CLK_PIN);
  INP_GPIO(SENSE_PIN);

  put_on_display("0123456789abcdefghijklmnopqrstuvwxy");

  return 0;

} // main


//
// Set up a memory regions to access GPIO
//
void setup_io()
{
   /* open /dev/mem */
   if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
      perror("can't open /dev/mem");
      exit(-1);
   }

   /* mmap GPIO */
   gpio_map = mmap(
      NULL,             //Any adddress in our space will do
      BLOCK_SIZE,       //Map length
      PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
      MAP_SHARED,       //Shared with other processes
      mem_fd,           //File to map
      GPIO_BASE         //Offset to GPIO peripheral
   );

   close(mem_fd); //No need to keep mem_fd open after mmap

   if (gpio_map == MAP_FAILED) {
      perror("mmap error");
      exit(-1);
   }

   // Always use volatile pointer!
   gpio = (volatile unsigned *)gpio_map;


} // setup_io

//
// Drop (root) privileges
//
void drop_privileges()
{
   /*  Drop superuser privileges in correct order */

   if (setgid(99) == -1) {
      perror("can't drop group privileges");
      exit(-1);
   }
   if (setuid(99) == -1) {
      perror("can't drop user privileges");
      exit(-1);
   }
} // drop_root

//
// Shift the bits provided in content into the display
//
void put_on_display(char *content)
{
   char *raw_output;
   int line;

   raw_output = malloc(7*(5+1));
   if (raw_output == NULL) {
      perror("malloc failed");
      exit(-1);
   }
   for (line=0; line<7; line++) {
      raw_output[line*6] = 1<<line;
      memmove(raw_output+1+6*line,content+5*line,5);
   }
   while (1);
   for (line=0; line<7; line++) {
      GPIO_CLR = 1<<GATE_PIN; // Licht an
      for (int byte=0; byte<6; byte++) {
         for (int bit=0; bit<8; bit++) {
            GPIO_CLR = 1<<SER_CLK_PIN;
            GPIO_ALTER((*(raw_output+6*line+byte)>>bit) & 0x01) = 1<<SER_DAT_PIN;
            GPIO_SET = 1<<SER_CLK_PIN;
         }
      }
      usleep(1000);
      GPIO_SET = 1<<GATE_PIN; // Licht aus
      GPIO_CLR = 1<<PAR_CLK_PIN;
      GPIO_SET = 1<<PAR_CLK_PIN;
   }
   free(raw_output);
} // put_on_screen