raspberry pi 2 toggle using gpiomem

rt.cpp

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

int main(int argc, char **argv)
{
  int fd ;
  const int max_p = sched_get_priority_max(SCHED_FIFO);
  printf("max=%d\n", max_p);
  const struct sched_param priority = { max_p }; // typically 1-low 99-high see man 7 sched
  sched_setscheduler(0,SCHED_FIFO, &priority);

  //Obtain handle to physical memory
  if ((fd = open ("/dev/gpiomem", O_RDWR | O_SYNC) ) < 0) {
    printf("Unable to open /dev/mem: %s\n", strerror(errno));
    return -1;
  }

  // map a page of memory to gpio at offset 0x20200000 which is where GPIO goodnessstarts
  static volatile uint32_t * const
    gpio = (uint32_t * const )mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x00200000);

  if ((int32_t)gpio < 0){
    printf("Mmap failed: %s\n", strerror(errno));
    return -1;
  }

  // set gpio17 as an output
  // increment the pointer to 0x20200004
  // set the value through a little bit twiddling where we only modify the bits 21-23 in the register
  *(gpio + 1) = (*(gpio + 1) & ~(7 << 21)) | (1 << 21);

  // toggle gpio17 every second
  while( 1 ) {
    // set the pin high
    // increment the pointer to 0x2020001C
    *(gpio + 7) = 1 << 17;

    // sleep
    //usleep(200-30);

    // set the pin to low
    // increment the pointer to 0x20200028
    *(gpio + 10) = 1 << 17;

    //usleep(300-30);
  }
}


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

int main(int argc, char **argv)
{
  int fd ;
  const struct sched_param priority = { SCHED_FIFO };
  sched_setscheduler(0,SCHED_FIFO, &priority);

  //Obtain handle to physical memory
  if ((fd = open ("/dev/gpiomem", O_RDWR | O_SYNC) ) < 0) {
    printf("Unable to open /dev/mem: %s\n", strerror(errno));
    return -1;
  }

  // map a page of memory to gpio at offset 0x20200000 which is where GPIO goodnessstarts
  static volatile uint32_t * const
    gpio = (uint32_t * const )mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x00200000);

  if ((int32_t)gpio < 0){
    printf("Mmap failed: %s\n", strerror(errno));
    return -1;
  }

  // set gpio17 as an output
  // increment the pointer to 0x20200004
  // set the value through a little bit twiddling where we only modify the bits 21-23 in the register
  *(gpio + 1) = (*(gpio + 1) & ~(7 << 21)) | (1 << 21);

  // toggle gpio17 every second
  while( 1 ) {
    // set the pin high
    // increment the pointer to 0x2020001C
    *(gpio + 7) = 1 << 17;

    // sleep
    //usleep(200-30);

    // set the pin to low
    // increment the pointer to 0x20200028
    *(gpio + 10) = 1 << 17;

    //usleep(300-30);
  }
}

toggle.cpp

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

static volatile uint32_t *gpio;

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

        //Obtain handle to physical memory
        if ((fd = open ("/dev/gpiomem", O_RDWR | O_SYNC) ) < 0) {
                printf("Unable to open /dev/mem: %s\n", strerror(errno));
                return -1;
        }


        //map a page of memory to gpio at offset 0x20200000 which is where GPIO goodnessstarts
        gpio = (uint32_t *)mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x00200000);

        if ((int32_t)gpio < 0){
                printf("Mmap failed: %s\n", strerror(errno));
                return -1;
        }

        //set gpio17 as an output
        //increment the pointer to 0x20200004
        //set the value through a little bit twiddling where we only modify the bits 21-23 in the register
        *(gpio + 1) = (*(gpio + 1) & ~(7 << 21)) | (1 << 21);

        //toggle gpio17 every second
        while(1){
                //set the pin high
                //increment the pointer to 0x2020001C
                *(gpio + 7) = 1 << 17;

                //sleep
                usleep(200);

                //set the pin to low
                //increment the pointer to 0x20200028
                *(gpio + 10) = 1 << 17;

                usleep(300);
        }
}